Publication 122M, Part 2, Chapter 3, Section 3.5
Surveying & Mapping Manual SURVEYING AND MAPPING MANUAL
TABLE OF CONTENTS
Part A - Engineering Field Surveys
Chapter Subject
Chapter 1 Measurements and Computations Chapter 2 Conventional Surveying Equipment and Supplies Chapter 3 Field Survey Classifications Chapter 4 Field Survey Procedures Chapter 5 Transferring Survey Data to CADD Chapter 6 Survey Types Chapter 7 Field Book Compilation, Format, and Recordings Chapter 8 Global Positing Surveys Chapter 9 Laser Scanners
Part B - Photogrammetric Aerial Photography and Mapping
Chapter Subject
Chapter 1 Project Development Chapter 2 Aerial Photography Acquisition Chapter 3 Targeting and Control Survey Chapter 4 Analytical Aero-triangulation Chapter 5 Digital Map Compilation Chapter 6 Digital Orthophotography Chapter 7 Digital Mapping Accuracy Testing Chapter 8 Electronic Media Preparation and Archiving
Appendices
A. Glossary of Terms B. Sample Field Book Entries C. Standard Forms D. Quality Assurance/Quality Control Plan for Development of Right-of-Way & Construction Plans
- I - PART A
ENGINEERING FIELD SURVEYS
PART A - ENGINEERING FIELD SURVEYS
TABLE OF CONTENTS
CHAPTER SUBJECT PAGE
CHAPTER 1 MEASUREMENTS and COMPUTATIONS
1.0 INTRODUCTION ...... A.1-1 1.1 UNITS OF MEASUREMENT ...... ….A.1-1 A. Distance ...... ….A.1-1 B. Angles ...... ….A.1-1 C. Area ...... ….A.1-1 D. Volume ...... …...... ….A.1-1 1.2 COMPUTATIONS ...... ….A.1-1 A. Significant Figures ... …...... ….A.1-1 B. Rounding ...... ….A.1-2 C. Stationing ...... ….A.1-2 D. Existing Surveys ...... ….A.1-2 E. Simple Curves ...... ….A.1-2 F. Transition (Spiral) Curves ...... ……...A.1-7 1.3 ACCURACY AND PRECISION ...... ….A.1-9 A. Horizontal (Length) Measurement Accuracy ...... ….A.1-10 B. Vertical (Elevation) Measurement Accuracy ...... ….A.1-10 C. Angular Measurement Accuracy ...... ….A.1-10 D. Control Traverse Accuracy Requirements ...... ……...A.1-10
CHAPTER 2 CONVENTIONAL SURVEYING EQUIPMENT and SUPPLIES
2.0 INTRODUCTION……………………………………….A.2-1 2.1 HORIZONTAL MEASUREMENT EQUIPMENT ..... ….A.2-1 A. Taping ...... …...... A.2-1 B. EDMI’s ...... …...... …. ....A.2-1 2.2 VERTICAL MEASUREMENT EQUIPMENT ..... …. ….A.2-1 A. Automatic Levels ...... ….A.2-2 B. Digital Levels……………………………………… ....A.2.2 C. Level Rods ...... …...... ……...A.2-2 D. Theodolites ...... …...... ……...A.2-2 2.3 ANGULAR MEASUREMENT EQUIPMENT….……...A.2-2 A. Transits ...... …...... A.2-2 B. Theodolites ...... …...... A.2-2 C. Total Station ...... A.2-3
- II -
CHAPTER SUBJECT PAGE
2.4 CALIBRATION of EQUIPMENT ...... A.2-3 A. Levels ...... A.2-3 B. Transits ...... A.2-4 C. Theodolites ...... A.2-5 D. EDMIs ...... ….A.2-5 2.5 MISCELLANEOUS EQUIPMENT ...... A.2-7 A. Transporting Equipment ...... A.2-7
CHAPTER 3 FIELD SURVEY CLASSIFICATIONS
3.0 INTRODUCTION ...... A.3-1 3.1 THREE - DIMENSIONAL SURVEYS ...... A.3-2 A. Geodetic Surveying and Computations ...... A.3-2 B. State Plane Coordinate System ...... A.3-4 C. Assumed Plane Coordinates ...... A.3-4 3.2 TWO - DIMENSIONAL SURVEYS ...... A.3-5 3.3 ONE - DIMENSIONAL SURVEYS (FLATCHAIN SURVEYS)...... A.3-5
CHAPTER 4 FIELD SURVEY PROCEDURES
4.0 INTRODUCTION ...... A.4-1 4.1 CONTROL TRAVERSES ...... A.4-2 4.2 CENTERLINE ...... A.4-3 4.3 REFERENCE MONUMENTATION ...... A.4-10 4.4 TOPOGRAPHY ...... A.4-12 A. Conventional Method ...... A.4-12 B. Total Station ...... …...... A.4-13 4.5 CROSS SECTIONS / PROFILES ...... A.4-13 A. Cross Sections ...... ……...... A.4-14 B. Profiles ...... …...... A.4-14 C. Total Station ...... …...... A.4-15 4.6 BENCH LEVELS ...... A.4-15 4.7 QUALITY CONTROL ...... A.4-15
CHAPTER 5 TRANSFERRING SURVEY DATA to CADD
5.0 INTRODUCTION ...... A.5-1 5.1 SURVEY PROCEDURES ...... A.5-1
CHAPTER 6 SURVEY TYPES
6.0 INTRODUCTION ...... … ….A.6-1 6.1 PRELIMINARY SURVEYS ...... A.6-1 A. Requirements ...... A.6-1 B. Procedures ..…...... ……………….... A.6-2
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CHAPTER SUBJECT PAGE
6.2 BRIDGE SURVEYS / WETLAND LOCATION SURVEYS HYDROLOGIC SURVEYS…………………………...... …….A.6-2 A. Requirements ...... …...... A.6-2 B. Procedures ...... A.6-3 6.3 CONSTRUCTION SURVEYS ...... ……………….A.6-4 A. Type A...... …...... A.6-4 B. Type B ...... …...... A.6-5 C. Type B Modified ...... …………………….A.6-5 D. Type C ...... …...... … …………….A.6-5 E. Type D ...... …… ...... A.6-6 F. Type D Modified ...... A.6-6 G. Procedures ...... …… ...... A.6-9 Bridge Stakeout ...... A.6-12 6.4 BORROW PIT SURVEYS ...... A.6-13 A. Requirements ...... A.6-13 B. Procedures ...... …...... A.6-13 6.5 FINAL SURVEYS...... A.6-14 A. Requirements ...... …………………….A.6-15 B. Procedures ...... …… ...... A.6-15 6.6 PROPERTY AND RIGHT-OF-WAY ACQUISITION SURVEYS..... A.6-17 A. Abandoned Canals and Railroad or Railway Right-of-Ways...……..A.6-18 B. Surveys within the Limits of a Public Utility Commission Order….. A.6-18 6.7 MECHANCIALLY STABILIZED EARTH WALLS………………… A.6-19 A. Initial Inventory…………………………………………………….. A.6-19 B. Routine Inventory……………………………………………………A.6-19 C. Movement Detected between Initial and Routine or Special Inventory…………………………………………………….A.6-19
CHAPTER 7 FIELD BOOK COMPILATION, FORMAT and RECORDINGS
7.0 INTRODUCTION ...... A.7-1 7.1 ACCEPTANCE REQUIREMENTS for CONSULTANT SURVEYS.. A.7-1 A. Preparation of Field Books ...... ………………...A.7-1 7.2 ABBREVIATIONS ...... ………………. A.7-2 A. General Abbreviations ...... ………...... A.7-2 B. Horizontal Curve Data Abbreviations ...... ………...... A.7-5 C. Transition (Spiral) Curve Data Abbreviations ... …………………….A.7-5 D. Vertical Curve Data Abbreviations ...... …… ...... ………………...A.7-5 E. Directional Abbreviations ...... …..………………...A.7-5 7.3 FIELD BOOK ENTRIES ...... ………………...A.7-6 A. Front Page ...... ………………...A.7-6 B. Alignment ...... …...... …………………….A.7-6 C. Topography ...... …...... …………………….A.7-6
- IV - CHAPTER SUBJECT PAGE
D. Cross Sections ...... …...... A.7-7 E. Profiles ...... …...... ………… …….A.7-8 F. Bench Levels ...... …...... A.7-8 G. Supervisor Check-off List for Form D-428 (survey field book)..A.7-8 H. Field Book Numbering………………………………………….A.7-9
CHAPTER 8 GLOBAL POSITIONING SURVEYS
8.0 INTRODUCTION ...... …….A.8-1 8.1 EQUIPMENT SPECIFICATIONS and CARE ...... …….A.8-1 A. Receiver Specifications ...... …...... …….A.8-1 B. Antenna Specifications ...... …….A.8-2 C. Tripod Specifications ...... …….A.8-2 D. Tribrach Specifications ...... …….A.8-2 E . Personnel Specifications ...... …….A.8-2 8.2 CONTROL SURVEYS - GENERAL...... …….A.8-3 A. Standards and Specifications ...... …….A.8-3 B. Classification of Accuracy ...... …...... …….A.8-3 C. Datums ...... …...... …….A.8-4 8.3 GLOBAL POSITION SYSTEM ...... …….A.8-5 A. Carrier Phase Tracking ...... …...... …….A.8-5 B. Code Tracking ...... …...... …….A.8-6 C. GPS Techniques ...... …...... …….A.8-6 D. Redundancy ...... …...... …….A.8-6 E . Specifications ...... …….A.8-6 F . Network Design ...... …...... …….A.8-6 G. Least Squares Adjustment ...... …….A.8-7 8.4 PRIMARY CONTROL NETWORKS ...... …….A.8-7 8.5 PROJECT SPECIFIC CONTROL NETWORKS ...... …….A.8-8 8.6 RTK SURVEYS – GENERAL ...... …….A.8-9 A. Real Time Kinematic ...... …….A.8-9 B. Kinematic Control Point ...... …...... …….A.8-9 C. Topo Point ...... …...... …….A.8-9 8.7 DELIVERABLES ...... …….A.8-9
CHAPTER 9 LASER SCANNERS
9.0 INTRODUCTION ...... …….A.9-1 9.1 TERRESTRIAL LASER SCANNERS ...... …….A.9-1 9.2 COORDINATE SYSTEM.…………………………………. …….A.9-2 9.3 HORIZONTAL/VERTICAL ACCURACIES…………………….A.9-2 9.4 POINT DENSITY and MEASURMENT PRECISION.………….A.9-2 9.5 OVERLAPPING SCANS…………………………………………A.9.2 9.6 DATA VOIDS……………………………………………………..A.9.2
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9.7 TARGETTING…………………………………………………A.9.3 A. Registration…………………………………………………. A.9.3 B. Supporting Imagery…………………………………………. A.9.3 9.8 WEATHER…………………………………………………….. A.9.4 9.9 DELIVERABLES……………………………………………... A.9.4 A. Survey Material Deliverables……………………………….. A.9-4 B. Project Deliverables………………………………………….A.9-4
- VI - A.1-1 CHAPTER 1
MEASUREMENTS AND COMPUTATIONS
1.0 INTRODUCTION
An understanding of measurements and computations is an essential aspect of the surveying profession. The basic units of measurement associated with length, angle, area, and volume will be discussed in further detail. The concept of significant figures as it relates to computational accuracies will also be discussed. Existing English unit survey data conversions to metric units is covered within Section 1.2 - Computations. Stationing and curve data representation in metric units is also provided, as they are integral pieces of survey computations. The terms precision and accuracy will be defined as they serve as important concepts related to the specific requirements of various types of surveys.
1.1 UNITS OF MEASUREMENT
The basic measurement determinations associated with surveying are related to distance, angle, area, and volume. These measurements are based on English units or (SI metric unit system).
A. Distance. US survey foot for measuring distance (length) is feet (ft) or metric base unit is meter (m).
B. Angles. Angular measurement is based on the sexagesimal system. This system is derived by dividing a circle into 360 degrees of arc. Each degree is then further divided into 60 minutes, with each minute being divided into 60 seconds. Therefore, the base units (and nomenclature) for angular measurements are degree ( ), minute ( ), and second ( ).
C. Area. In the English unit system, the base unit used to denote large land areas is the acre (ac), where 1 ac = 43,560 ft². Smaller land area measurements are based on the square foot. (SI metric unit system, the base unit used to denote large land areas is the hectare (ha), where 1 ha = 10,000 m², smaller land area measurements are based on the square meter (m²))
D. Volume. The base unit of volumetric measurement is the cubic yard (yd³) (cubic meter (m³)).
1.2 COMPUTATIONS
Before field data may be used for various purposes, it must be analyzed and adjusted (if necessary) to meet the specific application needs. Some of the basic concepts that should be considered when performing data reduction are discussed in this section.
A.1-2 A. Significant Figures. The number of significant figures recorded for a specific measurement is an indication of the accuracy attained. The number of significant figures for a measured quantity is defined as the number of sure or certain digits, plus one estimated digit. Computations involving the addition and subtraction of field measures result in an answer that does not contain significant digits farther to the right than occurs in the least precise number. The rule for multiplication and division is that the product or quotient will not contain more significant digits than are contained in the measurement with the fewest significant digits used in the multiplication or division.
B. Rounding. Computations involving field measurements are also influenced by rounding off number methodologies. When a figure is to be rounded to fewer digits than the total number available, the procedure is as follows:
When the first digit discarded is less than 5, the last digit retained should not be changed.
When the first digit discarded is greater than 5, or if it is a 5 followed by at least one digit other than 0, the last digit retained should be increased by one unit.
When the first digit discarded is equal to 5, followed by only zeros, the last digit retained should be rounded upward if it is an odd number, but no adjustment made if it is an even number.
C. Stationing. Stations designated at every 100 feet (1000 meters - kilometer). Stations will appear as 32 + 80.84 (1+000.000).
D. Existing Surveys. To convert existing survey data from English units to metric units, the US Survey Foot definition will be used. Multiply distances and coordinates in feet by 0.304 800 61 (1200 m/3937 ft) to obtain meters.
E. Simple Curves. Stationing along the arc length of the simple curve will be used for all computations. All curve data will be based on the radius in feet. For new survey baselines, the radius should be expressed in multiples of 10 feet (5 m) increments for use with curve data calculations. Existing survey simple curve data expressed in metric units will be converted to the exact English equivalent to the nearest 0.01 foot (1 mm). All simple curve data computations will be based on the information presented in Figure 1.2.1 and will adhere to Design Manual, Part 2, Chapter 2, Section 2.4.
A.1-3
General Formulas Legend T = R TAN (Δ/2) PI = Point of Intersection LC= 2R SIN (Δ/2) PC= Point of Curve E = T TAN (Δ/4) PT = Point of Tangent When 'R' is known, Δ = Deflection Angle E = R (SEC (Δ/2) - 1) = R EXSEC (Δ/2) T = Tangent M = E COS (Δ/2) E = External Distance When 'R' is known, R = Radius M = R (1 - COS (Δ/2)) = R VERS (Δ/2) M = Middle Ordinate L = πRΔ/180 LC= Long Chord (Distance between Locating the PC and PT, PC and PT) PC STA = PI STA - T C = Midpoint of Long Chord PT STA = PC STA + L L = Length of Curve
Figure 1.2.1 Simple Curve Computation Method
A.1-4 The example shown in Figure 1.2.2 uses the general formulas to convert a simple curve from English units to the metric equivalent.
(a) (b) (c) English "Soft" Metric Equivalent "Hard" Metric Equivalent PI STA 974+33.16 PI STA 29+697.687 PI STA 29+697.687 Δ = 27 47 14 Δ = 27 47 14 Δ = 27 47 14 D = 1 30 00 T = 287.986 m T = 288.170 m T = 944.83' L = 564.638 m L = 565.000 m L = 1852.48' R = 1164.253 m R = 1165.000 m R = 3819.72' E = 35.089 m E = 35.111 m E = 115.12' Figure 1.2.2 Simple Curves
Figure 1.2.2 (a) shows the traditional English unit curve data. Figure 1.2.2 (b) is the "soft" conversion results computed from English units (Figure 1.2.2 (a)) to the equivalent metric data. The "soft" conversion uses the US Survey Foot definition to compute an equivalent radius. Given the radius and deflection angle, all other curve data can be calculated. Figure 1.2.2 (c) is the metric curve data used to establish new survey baselines. This data approximates the curve data shown in Figure 1.2.2 (a).
An understanding of simple curve computations used to generate curve data represented on as-built plans is essential when utilizing the general formulas listed in Figure 1.2.1. As- built curve data is typically based on either chord-definition or arc-definition. The differences between chord-definition and arc-definition is illustrated in Figure 1.2.3 (from "Route Location and Design" by Thomas F. Hickerson, published by the McGraw-Hill Book Company).
A.1-5
(a) (b)
Figure 1.2.3 Arc-Definition vs. Chord-Definition
The key parameters used to develop as-built curve data will include Radius, R, or Degree of Curve, D. The relationship between these two parameters is different dependent upon the method used to establish the curve data (i.e. chord-definition or arc-definition). The Degree of Curve, D, is defined as either (in Figure 1.2.3 (a)) the central angle which subtends a 100 feet (30 m) arc or (in Figure 1.2.3 (b)) the central angle which subtends a 100 feet (30 m) chord. The derivations outlined in "Route Location and Design", by Thomas F. Hickerson, published by the McGraw-Hill Book Company, yield the following:
R = 5729.577951 / D, (arc-definition)
and
R = 50 / SIN ((1/2) D), (chord-definition)
where R = radius (in feet) D = degree of curve (in degrees)
Chord Method Conversion. The following example problem illustrates the conversion from the chord method, generated curve data to the metric equivalent.
A.1-6 (a) (b)
PI STA 1107+08.43 PI STA 33+743.997 Δ = 13 10 47 Δ = 13 10 47 D = 2 15 00 T = 89.672 m T = 294.20' L = 178.553 m L = 585.80' R = 776.217 m R = 2546.64' E = 5.163 m E = 16.94'
Figure 1.2.4 Chord Method Conversion
Figure 1.2.4 (a) is a typical as-built, English unit, curve data block. The individual curve information (i.e. T, L, etc.) is based on chord-definition computations. Chord-definition was employed on highway plans until the mid 1960's. The methodology used for these computations establishes a Radius, R, based on a Degree of Curve, D. Figure 1.2.4 (b) is the "soft" conversion results computed from English units (Figure 1.2.4 (a)) to the equivalent metric data. The "soft" conversion uses the US Survey Foot definition to compute an equivalent radius. Given the radius and deflection angle, all other curve data can be calculated using the general formulas presented in Figure 1.2.1.
Arc Method Conversion. The following example problem illustrates the conversion from the arc method, generated curve data to the metric equivalent.
(a) (b)
PI STA 974+33.16 PI STA 29+697.687 Δ = 27 47 14 Δ = 27 47 14 D = 1 30 00 T = 287.986 m T = 944.83' L = 564.638 m L = 1852.48' R = 1164.253 m R = 3819.72' E = 35.089 m E = 115.12'
Figure 1.2.5 Arc Method Conversion
Figure 1.2.5 (a) is a typical as-built, English unit, curve data block. The individual curve information (i.e. T, L, etc.) is based on arc-definition computations. The methodology employed for these computations establishes a Radius, R, based on a Degree of Curve, D. Figure 1.2.5 (b) is the "soft" conversion results computed from English units (Figure 1.2.5 (a)) to the equivalent metric data. The "soft" conversion uses the US Survey Foot definition to compute an equivalent radius. Given the radius and deflection angle, all other curve data can be calculated using the general formulas presented in Figure 1.2.1. A.1-7 F. Transition (Spiral) Curves. Stationing along the arc of spiral curves will be used for all computations. The circular curve data will be based on the radius in meters. For new survey baselines, the radius should be expressed in multiples of 10 feet (5 m) increments for use with spiral curve data calculations. Existing survey spiral curve data expressed in metric units will be converted to the exact English equivalent by "soft" conversion to the nearest 0.01 foot (mm) using the general formulas listed in Figure 1.2.6. All spiral curve data computations will adhere to Chapter 2, Section 2.16 of Design Manual, Part 2.
A.1-8 General Formulas Legend TS = (RC + p) TAN (Δ/2) + k TS = Tangent to Spiral Point θS = (LS/60.96012192) x (1746.378852/RC) SC = Spiral to Curve Point ΔC = Δ - 2θS CS = Curve to Spiral Point ES = (RC + p) EXSEC (Δ/2) + p ST = Spiral to Tangent Point LC = (30.48006096ΔC) / (1746.378852/RC) TS = Tangent Distance p = ("p" constant, Table II) x LS RC = Radius of Circular Curve k = ("k" constant, Table II) x LS p = Simple Curve Co-ordinate LC = ("LC" constant, Table II) x LS (Ordinate) LT = ("LT" constant, Table II) x LS Δ = Deflection Angle ST = ("ST" constant, Table II) x LS k = Simple Curve Co-ordinate xC = ("xC" constant, Table II) x LS (Abscissa) yC = ("yC" constant, Table II) x LS θS = Spiral Angle LS = Spiral Length 2 2 θ = (L /LS ) x θS ΔC = Central Angle Between the y = ("y" constant, Table II) x L SC and CS ES = External Distance LC = Length of Circular Curve LC = Long Chord LT = Long Tangent Table II constants from ST = Short Tangent "Transition Curves for Highways" xC = Tangent Distance for SC by Joseph Barnett yC = Tangent Offset of the SC
Figure 1.2.6 Spiral Curve Computation Method
The reference books for spiral curve computations are "Transition Curves for Highways" by Joseph Barnett and "Route Location and Design" by Thomas F. Hickerson, published by the United States Printing Office and McGraw-Hill Book Company, respectively. Spiral curve computations to convert as-built curve data to the metric equivalent will be based on the original arc-definition as described in the previous section. The minimum data shown for the spiral alignment will be in accordance with Design Manual, Part 3, Chapter 2, Section 2.6.
The example shown in Figure 1.2.7 uses the general formulas to convert a spiral curve from its English units to the metric equivalent.
A.1-9 (a) (b) (c) English "Soft" Metric Equivalent "Hard" Metric Equivalent PI STA 831+24.21 PI STA 25+336.310 PI STA 25+336.310 Δ = 36 20 16 Δ = 36 20 16 Δ = 36 20 16 ΔC = 28 50 15.99 ΔC = 28 50 15.99 ΔC = 28 48 26.92 DC= 2 30 00 RC = 698.551 m RC = 700.000 m RC = 2291.83' LC = 351.591 m LC = 351.950 m LC= 1153.51' θS = 3 45 00 θS = 3 45 54.54 θS = 3 45 00 LS = 91.440 m LS = 92.000 m LS = 300.00' TS = 275.129 m TS = 275.886 m TS = 902.65' ES = 37.180 m ES = 37.262 m ES = 121.98' k = 45.714 m k = 45.994 m k = 149.98' p = 0.498 m p = 0.503 m p = 1.63' XC = 91.401 m XC = 91.960 m XC= 298.71' YC = 1.994 m YC = 2.015 m YC= 6.54' LT = 60.974 m LT= 61.347 m LT= 200.04' ST = 30.492 m ST = 30.679 m ST= 100.04' LC = 91.426 m LC= 91.982 m LC= 299.94'
Figure 1.2.7 Transition (Spiral) Curves
Figure 1.2.7 (a) shows the traditional English unit curve data. Figure 1.2.7 (b) is the "soft" conversion results computed from English units (Figure 1.2.7 (a)) to the equivalent metric data. The "soft" conversion uses the US Survey Foot definition to compute an equivalent radius. Given the radius, deflection angle, and spiral length, all other curve data can now be calculated. Figure 1.2.7 (c) is the metric curve data used to establish new survey baselines. This data approximates the curve data shown in Figure 1.2.7 (a).
1.3 ACCURACY AND PRECISION
Surveying measurements must be made with a specific degree of precision in order to attain a suitable level of accuracy for the task at hand.
Precision refers to the degree of consistency among a group of measurements. If the result of a group of measurements yields a small discrepancy (between the measured and actual value) then the result of the survey is precise. This degree of consistency is dependent on instrument sensitivity and observer skill.
Accuracy refers to the degree of conformity of measurements to the true value. If each measurement within a group of measurements yields small discrepancies (between the measured and actual value) then the survey is accurate.
A.1-10 A. Horizontal (Length) Measurement Accuracy. Horizontal distances must be measured and expressed to 0.01 foot (1 mm). These measurements must meet the accuracy requirements for the specific Order and Class of survey as outlined in Table 1.3.1 for the survey classifications described in Part A, Chapter 3 - Field Survey Classifications. Some of the types of equipment used to attain these accuracies are described in Part A, Chapter 2 - Surveying Equipment and Supplies, Section 2.1 - Horizontal Measurement Equipment.
B. Vertical (Elevation) Measurement Accuracy. Vertical elevations must be measured and expressed to 0.01 foot (1 mm). These measurements must meet the accuracy requirements for the specific Order and Class of survey as outlined in Table 1.3.2 for the survey classifications described in Part A, Chapter 3 - Field Survey Classifications. Some of the types of equipment used to attain these levels of accuracy are described in Part A, Chapter 2 - Surveying Equipment and Supplies, Section 2.2 - Vertical Measurement Equipment.
C. Angular Measurement Accuracy. Angular measurements must be recorded and expressed to the nearest 1 second. These angular measurements must meet the specific accuracy requirements as outlined in Table 1.3.1 and Table 1.3.2 for the survey classifications described in Part A, Chapter 3 - Field Survey Classifications. The instruments used for angular measurement are described in Part A, Chapter 2 - Surveying Equipment and Supplies, Section 2.3 - Angular Measurement Equipment.
D. Control Traverse Accuracy Requirements. All survey work related to horizontal control networks will be categorized as shown in Table 1.3.1. Table 1.3.1 is a compilation of information outlined in "Standards and Specifications for Geodetic Control Networks" by the Federal Geodetic Control Committee.
A.1-11 Table 1.3.1 Horizontal Control Accuracy Requirements
ORDER Third Third Flatchain CLASS I II
DIRECTIONS Number of Positions or Sets...... ………. 4 2 NA Standard Deviation of Mean not to Exceed...... …….. 1.2" 2.0" NA Rejection Limit from the Mean...... ……. 5" 5" NA
ASTRONOMICAL AZIMUTHS1 Astronomical Azimuth Spacing not more than (Segments)2...... …………… 25 40 NA Observations per Station……………… 8 4 NA Standard Deviation of Mean not to Exceed...... ……. 1.0" 1.7" NA Rejection Limit...... ……. 6" 6" NA
ANGLE MISCLOSURE [Σ=(n-2)180 ]3 Average not to Exceed...... 3.0" 5.0" NA
DISTANCE Minimum Distance Precision...... 1:25 000 1:15 000 1:1000
CLOSURE IN POSITION Azimuth Closure at Azimuth Check 4 Point ...... 10.0 N 12.0 N NA
Position of Closure after Azimuth 1.6 M 3.2 5 NA Adjustment ...... or meters or meters
0.40 K 0.80 K or or 1:10 000 1:5000
1 Astronomical azimuths based on observation of Polaris at any hour angle, except as otherwise indicated in Chapter 3 - Classification of Surveys. 2 See Chapter 3 - Classification of Surveys for additional requirements. 3 Based on the difference between the sum of the measured angles and the geometrically correct total of the control traverse polygon. n is the number of sides, or angles, in the control traverse. 4 Seconds of arc, where N is number of segments. 5 Maximum feet (meters) of difference between computed and fixed values, where M (K) is route distance in miles (kilometers) (for longer lines) and proportional expression is route distance in feet (meters). Use the formula that provides the smallest permissible closure. A.1-12
All survey work related to vertical control networks will be categorized as shown in Table 1.3.2. Table 1.3.2 is a compilation of information outlined in "Standards and Specifications for Geodetic Control Networks" by the Federal Geodetic Control Committee.
Table 1.3.2 Vertical Control Accuracy Requirements
ORDER Third Flatchain
LEVELING Maximum Sight Length feet (m)...... 300’ (90) NA Difference of Foresight and Backsight never to Exceed.…. 100’ (10) NA Minimum Ground Clearance of Line of Sight feet (m)....… 1.5’ (.5) NA
LOOP MISCLOSURE Loop Misclosure not to Exceed (feet)….………………. 0.039 1.609M NA (meters)……………….. (0.012 K )
M - Perimeter of loop in miles. K - Perimeter of loop in kilometers. A.2-1
CHAPTER 2
CONVENTIONAL SURVEYING EQUIPMENT AND SUPPLIES
2.0 INTRODUCTION
This chapter outlines various survey measurement equipment necessary to perform specific engineering field surveys as discussed in Part A, Chapter 6 - Field Surveys. Horizontal, vertical, and angular measurement equipment for both conventional (transit and chain) surveying methods and total station surveying methods are included with consideration to accuracy requirements previously outlined in Part A, Chapter 1 - Measurements and Computations.
2.1 HORIZONTAL MEASUREMENT EQUIPMENT
Several different distance measurement devices may be used with field surveying. The most common horizontal (distance) measurement methods employ either taping or electronic distance measuring instruments (EDMI). The precision of these distance measurement devices contributes to overall accuracy of the specific survey task. Precisely calibrated distance measurement devices, combined with proper field survey techniques (Part A, Chapter 4 - Field Survey Procedures), will satisfy the most stringent accuracy requirements such as location and stake-out of major structures. This will also provide flexibility to round or truncate measurement value when the highest degree of accuracy is not needed. All measurement devices described here will result in accuracies meeting the requirements previously outlined in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision.
A. Taping. For conventional taping methods, measuring distances in feet (meters) to a precision of 0.01 foot (1 mm) as discussed in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision. This is possible with available English (metric) tapes in varying lengths of 100 feet and 300 feet (30 and 50 meters) graduated to 0.01 foot (2 mm) increments. Folding rules and retractable hand tapes are also available with 0.01 foot (1 mm) graduations.
B. EDMIs. Electronic distance measuring instruments have selective "coarse" and "fine" measurement modes. In the "coarse" mode, distances are measured and displayed to 0 .01 foot (1 mm). In "fine" mode, distances are measured and displayed to 0.001 foot (0.0001 m). EDMI’s precision should exceed 0.01 foot (1 mm) requirement as discussed in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision.
2.2 VERTICAL MEASUREMENT EQUIPMENT
There are several methods for measuring vertical distances and computing elevations at points. Differential leveling is the most common method for measuring vertical distances. Differential leveling is based on establishing a horizontal line of sight to determine relative A.2-2
elevations at a specific location. All measurement devices described here, along with the proper field survey procedures (Part A, Chapter 4 - Field Survey Procedures) will result in accuracies meeting the requirements previously outlined in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision.
A. Automatic Levels. Automatic levels include a self-leveling feature, which reduces the set-up time of the operation. Most automatic levels have to be "roughly" leveled using a three-screwed leveling head to center a bull's-eye bubble. Once this has been accomplished, a compensator will then "fine-tune" the instrument and establish a level line of sight.
B. Digital Levels. Digital levels use electronic image processors to determine heights, distances and record data automatically. Digital levels are to be used for long level loops. Digital levels are not recommended for short level loops.
C. Level Rods. An English rod graduated in 0.01 foot (1 mm) intervals will be required for use with vertical measurement procedures. These English (metric) rods can be read and interpolated to the nearest 0.005 foot (1 mm). Third Order leveling requires a geodetic level a wooden, invar, fiberglass bar coded or calibrated fiberglass rod for differential leveling. The rods must not be more than 12 feet (4 m) in length.
D. Theodolites. Theodolites consist of a sighting telescope with graduated horizontal and vertical circles. The vertical angle measurement obtained from a theodolite can be combined with the horizontal measurement obtained from an EDMI to produce vertical distances. There are generally two types of scales used with theodolites. They are either direct reading optical scales or optical micrometer scales. Vertical angle measurements using a direct reading optical scale can be read to the nearest 1-minute. Vertical angular measurements using an optical micrometer scale can be read to the nearest 3 seconds.
2.3 ANGULAR MEASUREMENT EQUIPMENT
Angular measurement instruments that display degrees ( ), minutes ( ), and seconds ( ), along with proper field survey procedures (Part A, Chapter 4 - Field Survey Procedures), will provide the accuracies indicated in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision.
A. Transits. Transits consist of an alidade, a circle, and a leveling head. When properly operated, transits will yield both horizontal and vertical angle measurements meeting the requirements established in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision.
B. Theodolites. As mentioned in Section 2.2 - Vertical Measurement Equipment, theodolites can be used to precisely measure both horizontal and vertical angles to obtain accuracies meeting requirements outlined in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision.
A.2-3
C. Total Station. A total station instrument combines a digital electronic theodolite, an electronic distance meter (EDM) device, and a built-in microprocessor (or computer). These total station devices can automatically measure both horizontal and vertical distances and determine both station coordinates and elevations. All information, distance, and angular measurements are recorded in the instrument's microprocessor. This information can then be transferred to an office computer and be readjusted as required.
2.4 CALIBRATION OF EQUIPMENT
Survey measurement equipment is expensive and extra care must be used by those handling and using precision instruments to secure satisfactory service and avoid excessive repairs and adjustments. Careless use and handling of engineering equipment will impair the accuracy of work performed.
All survey measurement equipment will be checked and calibrated on a routine basis. All equipment must be checked every 6 months and/or at the beginning of a long duration project. There are currently 11 locations in Pennsylvania from which the equipment can be calibrated. Information on these locations is compiled and published by the National Oceanic and Atmospheric Administration, National Geodetic Survey (NGS).
The following information is printed as a guide for qualified instrument operators and survey party chiefs in accomplishing field adjustments of the levels, transits, theodolites, and EDMI’s. All adjustment procedures presented will be performed in lieu of manufacturer's instructions. Any adjustment of survey measurement instruments must be done by experienced personnel or under the direct supervision of qualified personnel. Extreme caution will be utilized in all tests and adjustments of surveying instruments to attain the highest degree of accuracy. Complications will arise if a faulty test shows need to adjust an instrument that stands already in good adjustment. Therefore, it is wise to test an instrument twice before attempting any adjustment.
A. Levels. All adjustments to levels are performed to establish a horizontal plane of sight when revolving the telescope of the level about its vertical axis. After all adjustments are made, the axis of sight, the axis of level bubble, and the axis of level bar will all be oriented parallel to each other and perpendicular to the vertical axis. The following procedures are required to properly adjust leveling instruments:
Adjustment of the Level Vial. These procedures will assure that the axis of the level bubble is perpendicular to the vertical axis. Set the level up assuring that the tripod is sturdily placed. Level the instrument over both sets of screws. With the level standing perfectly level over one set of screws, rotate the level tube and level vial 180 about its vertical axis. If the instrument stands level, then no adjustment is required. However, if the bubble does not center, then adjust one half the error by use of the capstan nuts at the end of the level tube. Re-level and repeat the same operation until satisfactory results are obtained.
Horizontal Alignment of Cross Hair. These procedures will assure that the horizontal cross hair is truly horizontal when the instrument is leveled. Sight the horizontal cross A.2-4
hair on a well-defined point by use of the leveling screws. Revolve the telescope about its vertical axis while observing the horizontal cross hair traverse the defined point. If the entire horizontal cross hair traverses on the point, then no adjustment is required. However, if the cross hair departs from the point, then loosen the two adjacent capstan screws and tap the cross hair reticule lightly until the desired effect is obtained. When satisfactory results are obtained, tighten the capstan screws to maintain the corrected position.
Line of Sight Adjustment. This test will show if the line of sight through the horizontal cross hair is parallel to the axis of the level tube or vial. Procedures outlined are commonly referred to as the Two Peg Test. Place two pegs preferably about 300 feet (100 m) apart. Set up the level equidistant between the two pegs. Observe the difference in elevation by sighting a level rod on each peg. This difference will be the true difference in elevation because any error would compensate itself due to equal sights. Then move the level to either one of the two pegs. Set up the level so that by looking through the objective end of the instrument, the eyepiece will be about 0.01 foot (3 mm) from the rod. After leveling, read a rod on the near peg by placing a pencil point on the rod and observing backward through the telescope. Compute the desired rod intercept of the second rod from the previous rod reading and the known difference in elevation. Observe the far rod. If the desired rod intercept is observed, then no adjustment is necessary. However, if the instrument is out of adjustment, then bring the line of sight to the desired rod intercept by moving the cross hair reticule vertically with the capstan screws. After the first adjustment, the test should be repeated to insure results.
Additional adjustments to the leveling instrument may be required because of parallax errors. Parallax errors are caused by faulty focusing of an instrument. Evidence of parallax occurs when the observer moves his eye from side to side while sighting through the telescope and sees an apparent movement of the cross wires over the object being observed. Each individual observer points the telescope toward the sky or a similar bright background and focuses the eyepiece to bring out a sharp cross wire image. This focus may vary due to the difference of each individual's eyes. The observer then properly focuses on the object by use of the objective focus and thereby has eliminated the apparent parallax.
B. Transits. All adjustments to transits are performed to precisely measure both vertical and horizontal angles. As with level calibrations, specific lines and axes of a transit must be properly positioned to obtain a well-adjusted instrument. The following procedures are required to properly adjust transits:
Plate Levels. In order that each plate level bubble remains centered when turning a transit to different positions, the axis of each plate level must be perpendicular to the vertical axis of the transit. Level the transit with each plate level vial parallel to a pair of opposite leveling screws. Then rotate the telescope 180 about the vertical axis. If the vials are still level, then no adjustment is necessary. However, if either of the bubbles does not remain centered, then adjust half the error by means of the screws on A.2-5
the plate levels. Re-level and repeat the same operation until satisfactory results are obtained.
Vertical Alignment of Cross Hair. These procedures will assure that the vertical cross hair is perpendicular to the horizontal axis of the instrument. Sight the vertical hair on a well-defined point, clamp both upper, and lower tangent clamps. Move the telescope in a vertical direction and observe the vertical cross hair as it passes along the sighted point. If the hair traverses on the point, the line of sight is in a plane perpendicular to the horizontal axis of the transit and no adjustment is necessary. However, if the vertical hair moves off the point, then loosen the two adjacent capstan screws on the cross hair reticule and turn the ring slightly until the desired effect is achieved. Now tighten the capstan screws to the desired snugness.
Collimation of Vertical Cross Hair. A common operation of the conventional transit is known as double-centering. This is a method of correcting an error caused by the line of sight not being perpendicular to the horizontal axis of the transit. Make a standard setup with the transit. With the telescope direct, sight a well-defined distant point. Now plunge or "flop" the scope and mark the line of sight about the same distance away as the original sight. Unclamp the one tangent screw; rotate the telescope 180 on its vertical axis, and again sight the original point using a flop sight. Now plunge the telescope to its direct position and mark this line of sight on or along side of the previously marked point. If the two points are the same, then no adjustment is necessary. However, if the two points are not the same, mark a point one-fourth the difference from the last marked point and adjust the vertical wire to that point. This is done by adjusting the capstan screws on the sides of the cross hair reticule. After an adjustment is made, another test should be run to verify results.
As with levels, additional adjustments may be required because of parallax errors. The procedures previously described for correcting parallax errors with levels are also applicable for transit adjustments.
C. Theodolites. Adjustment procedures are generally the same for all models of theodolites. The bubble in the bull's-eye spirit vial is centered by using the three leveling screws. The tubular spirit vial is then adjusted to assure that the top plate is parallel with an imaginary line created by any two of the leveling screws. The bubble located within the tubular spirit vial is then centered by adjusting the two corresponding leveling screws. The alidade is rotated 90 degrees and the bubble in the tubular spirit vial is readjusted using the previously "unused" leveling screw. This procedure is repeated until the bubble in centered for all instrument positions.
D. EDMI’s. All EDMI’s will be carefully adjusted and precisely calibrated in order to obtain the required accuracies as indicated in Part A, Chapter 1 - Measurements and Computations, Section 1.3 - Accuracy and Precision. However, it should be noted that these instruments will still exhibit a small, but constant, instrumental error and an error that is proportional to the distance measured. These two pieces of information are compiled and are presented as the specification for the instrument. A typical instrument specification is:
(0.02 foot (6 mm) + 5 ppm) A.2-6
The first number, 0.02 foot ( 6 mm), is an indication of the precision of the instrument (constant instrumental error). This specification implies that the distances measured will be within 0.02 foot (6 mm) from the mean of a group of measurements. The second number, 5 ppm, is an indication of the attainable accuracy levels. This specification implies that the distances measured will be within 5 parts per million of the true distance. Accuracy adjustments to the EDMI’s will require a test range as specified in the information compiled and published by the National Oceanic and Atmospheric Administration, National Geodetic Survey. Prior to making any adjustments at the test range, all optical plummets should be checked. All offset changes should be made in accordance with the manufacturers’ manual. In addition, all prisms that will be used on a daily basis with the EDMI should be used when calibrating the instrument. The following are the accuracy adjustment procedures required when calibrating an EDMI:
Place and level the EDMI over the "0" monument of the calibrated baseline.
Place the prism over the first monument of the calibrated baseline range. Be certain that the prism offset established in the EDMI is the same as that of the prism located at the first monument.
Apply all correction factors, as specified by the manufacturer, to the EDMI to account for various atmospheric conditions (such as atmospheric pressure, temperature, and humidity).
Measure and record 10 to 15 measurements. Compare the mean reading with the true value from the calibrated baseline information sheet provided by the National Geodetic Survey. Care should be exercised to ensure that the measured distances have been reduced to their horizontal equivalents.
If the mean reading and the true value are not the same, then the EDMI must be adjusted. Fine adjustment procedures to the prism offset are available with the specific dealer of the instrument.
Once the EDMI has been adjusted, move the prism to another identified monument and measure and record 10 to 15 measurements. Compare these results with the calibrated baseline information and verify that the manufacturer's specifications are exceeded.
Unlike accuracy adjustment procedures, precision determination can be accomplished without the use of a calibrated baseline test range. The following are recommended precision determination procedures:
Place the EDMI on a sturdy tripod.
Place a prism 300’ (90 m) away on a prism pole and measure and record 10 to 15 measurements. Discard the first measurement taken after the EDMI has been turned on.
Compare the mean reading value with each measurement. If the difference between the two values exceeds the manufacturer's specifications, then the instrument will need to be serviced. A.2-7
2.5 MISCELLANEOUS EQUIPMENT
Additional surveying equipment and supplies may be necessary to complete specific engineering field surveys as discussed in Part A, Chapter 6 - Survey Types. The following is a list of these items that may prove useful when performing a specific survey:
EQUIPMENT: Survey Vehicle Straight Edges Transit, Theodolite, EDMI Engineer's Scales Tripods Screwdrivers Level Rods Adjusting Pins Sight Rods PK Nails Targets Protractors 30 m Fiberglass Tape Triangles Locke Levels and Cases Solar Eye Pieces Plumb Bobs and Cases Metallic Tape 2 m Folding Rule Flagmen Vests Hand Axes 5' Jake Staff Large Axes Magnetic Compass Sledgehammers Meat Hook Brush Hooks Prisms Caution Signs and Flags Prism Pole Tape Repair Outfit
SUPPLIES: Metallic Tape Fillers--Exchangeable Crayon (Blue, Yellow, Red) Steel Tape Fillers--Exchangeable Survey Ribbon (various colors) Glasses for Locke Levels Field Books Plumb Bob String 1st Aid Kit Plumb Bob Points Envelopes Stakes Pen Holders Survey Tacks Stationery Calculators Publication 213 "WZTC Guide" Surveying and Mapping Manual (Pub 122M)
A. Transporting Equipment. Survey crews will ordinarily carry their full equipment in their survey vehicle; to have it available at all times in the line of duty. Extreme care will be used in packing equipment, especially precision instruments, to avoid damage by jolting, scratching or rubbing. Instruments will be placed in their cases and the cases protected by suitable material that will absorb the shock and vibration. A.3-1 CHAPTER 3
FIELD SURVEY CLASSIFICATIONS
3.0 INTRODUCTION
Field survey classifications are based on reaching a balance between the complexity of design and construction (accuracy) and the sophistication of survey techniques employed (precision). Relatively complex design and construction on a new location requires a high degree of accuracy and would require a more precise survey. Conversely, relatively simple construction projects (maintenance, resurfacing, etc.) do not require a high degree of accuracy and can be accomplished with a less precise survey.
Many factors effect the selection of survey requirements for a project. The following factors should be considered in the evaluation and decision making process:
Location. New location would require accurate monumentation for staking the design during construction. Horizontal and vertical monumentation would be required to reestablish alignment and elevation throughout the construction operations and to prepare final plans (as-builts). Projects on existing location would require less monumentation for staking and may not require vertical control or horizontal alignment.
Complexity. Complex projects involving interchanges, intersecting side roads and large bridges would require accurate monumentation. Horizontal and vertical monumentation would also be required to reestablish alignment and elevation. Projects involving simpler design and construction would require less monumentation and may not require vertical control or horizontal alignment.
Database. Availability of data for the performance of a project survey has a direct bearing on the requirements. As an example, a project on new location with photogrammetric mapping will require relatively precise horizontal and vertical control surveying to ensure that the measurements, computations, monumentation, and staking meet required accuracies. Another example would be a project on new location without photogrammetric mapping. The project would require the same precision for monumentation of the horizontal and vertical alignment control but would require additional precise control traversing to tie the projects' datum to the geodetic reference system.
Project Variability. An individual project may have several classifications of surveys in response to a combination of design and construction requirements. As an example, a reconstruction project on existing location with mainline resurfacing and with widening at an intersection would require alignment staking and horizontal resurfacing of the mainline with additional vertical control and resurfacing in the area of the widening. Survey requirements must fit the project needs.
A.3-2 Field survey classifications should be selected to meet the project requirements. Careful evaluation of the project requirements with respect to the selection of survey procedures and methods should be undertaken during the scoping process.
3.1 THREE - DIMENSIONAL SURVEYS
Classification of field surveys consists of establishing horizontal and vertical control with referenced monumentation. Horizontal control refers to the position of a point with respect to a standardized frame of reference. There are three recognized standards as follows:
Geodetic. Position is based on location on a regular mathematical surface (ellipsoid) formed by rotation about the minor axis (earth's polar axis). Location east and west is expressed in degrees ( ), minutes ( ), and seconds ( ) of longitude, and location north and south is expressed in degrees ( ), minutes ( ), and seconds ( ) of latitude. Elevation is the third parameter, which is a significant element in the computations. National Geodetic Survey (NGS) has compiled all horizontal control data for the reference network in meters and converted all points to the local State Plane Coordinate System.
State Plane Coordinate System (SPCS). Position is based on converting geodetic positions of a portion of the earth's surface to a plane rectangular surface. Points are projected mathematically to an imaginary surface, which can be developed (unrolled or laid out), without distortion of shape or size. A rectangular grid is superimposed on the developed surface and the position of the points is referenced to the grid axis. Grid lines running east - west are called northings and those running north - south are called eastings.
Assumed Plane Coordinates. Position is based on Cartesian coordinate (rectangular) system or a flat surface. This is represented with an arbitrary grid system of northings and eastings.
The three reference systems are different from one another somewhat in the surveying techniques employed and very different in the computational procedures. The common factor in all three is the vertical reference system. Prior to January 1, 1996, vertical control was based on the National Geodetic Vertical Datum of 1929 (NGVD 29). Thereafter, all vertical control must be established based on the newly adopted North American Vertical Datum of 1988 (NAVD 88). Assumed, arbitrary, or approximate elevations may not be used for three-dimensional surveys. Differential spirit levels will be run for all vertical control on all traverse control points. Trigonometric leveling is not allowed.
A. Geodetic Surveying and Computations. This sub-classification of three- dimensional surveys will, in all likelihood, constitute the least frequent with respect to highway route surveys, since the project would require state plane coordinate reference without aerial photogrammetry and mapping. This survey is the type required to A.3-3 establish network control for aerial photogrammetry as discussed in Part B of this manual.
The survey would preferably consist of precision traversing between at least two National Geodetic Reference System (NGRS) stations with the traverse serving as the project's control traverse (along the proposed alignment). First and Second Order stations are preferred, but Third Order stations are acceptable if the traverse control points are occupied twice and astronomical observations for azimuth is completed at one control point along the control traverse within the limits of the proposed alignment. Stations which do not have azimuth sightings, or the sightings are not visible will also require astronomical observation for azimuth.
Precision traversing from a single horizontal station will be considered if the distance to a second station is excessive 6 miles (greater than 10 km) and the length of the traverse is increased by looping. The loop could be on the forward or return leg of the traverse and must be physically separate from the other leg. The loop legs will be far enough away from one another to create a minimum ratio of 3:1 (length of longest leg: perpendicular distance to other leg). Astronomical observations for azimuth will be taken on each leg. Intervisible control points on each loop will be occupied with angles and distances obtained.
Procedures will be carried out to check the accuracies of the traversing and leveling. Unacceptable accuracies will be resolved prior to computations of SPCS coordinates.
By state law, effective January 1, 1996, all Pennsylvania State Plane Coordinate System information will be computed in the North American Datum of 1983 (NAD 83). By policy decision, effective January 1, 1996, all vertical survey information will be computed in the North American Vertical Datum of 1988 (NAVD 88).
Prior to January 1, 1996, North American Datum of 1927 (NAD 27) and the National Geodetic Vertical Datum of 1929 (NGVD 29) was used.
Surveys will be balanced in accordance with Chapter 4 "State Plane Coordinate System of 1983" by the National Geodetic Survey. From which NGS has compiled new standards and constants for each state as part of the newer horizontal control network which is referred to as the State Plane Coordinate System of 1983 (SPCS 83). Subsequent surveys using these control stations may require adjustment from grid azimuths and distances.
Ground level distances are be derived by dividing the grid distance by the grid factor (product of scale factor and elevation factor). For most survey projects, a single combined factor can be computed and used to reduce all measured ground distances to grid distances. A single combined factor can be computed by multiplying the elevation factor by the grid factor. The combined factor is to be included in the general notes of the plan.
Ground level angles (and bearings) may be very close and acceptable for field use without further consideration. The decision to adjust grid azimuths for field use must be based on the significance of the adjustments with respect to the precision of the instrument. A.3-4 Additional computational procedures are outlined in Part B of this manual.
Global Positioning System (GPS) survey techniques can be substituted for precision traversing. Network design observations and computations are discussed in Part B of this manual. Intervisibility of pairs is necessary for subsequent traversing and setting alignment.
Alignment, topography, ground elevations, and other survey procedures will all be based on the network control system. Chapter 4 - Field Survey Procedures contains the procedures to be used for these field survey operations.
B. State Plane Coordinate System. This sub-classification of three-dimensional surveys will be the most frequent for larger or complex projects on new alignment, since aerial photogrammetry and mapping would be a required element for most of these projects. This survey uses the control network from the aerial control survey as the basis for all subsequent work. Therefore, copies of the original field survey notes of the control traverse and the adjusted (and unadjusted) traverse data must be obtained. Adjustment procedures for ground level distances and azimuths would be made as previously outlined under Section 3.1.A – Geodetic Surveying and Computations. The survey work would consist of precision traversing (Third Order, Class I accuracies) between aerial control network stations to establish the project's control traverse. This will be necessary since the aerial network layout would normally straddle the projects alignment. Traversing between stations, closed loops, triangulation, or combinations of these techniques will be employed to develop the project control traverse.
Traversing and leveling will be checked for accuracy. Unacceptable accuracies will be resolved prior to computation. Acceptable surveys will be balanced and coordinated from the aerial network coordinates.
Alignment and other survey procedures will be based on the project's control traverse. See Chapter 4 - Field Survey Procedures for the requirements for these other field survey procedures.
C. Assumed Plane Coordinates. This sub-classification of three-dimensional surveys will be the most frequently employed, since the larger percentage of projects will fall in this category. This survey consists of reestablishing an existing alignment by either direct or indirect methods. The direct method involves retracing the centerline or baseline by occupying the alignment control points. The indirect method consists of reconstructing the centerline or baseline by paralleling or random traversing.
Direct occupation of the centerline or baseline requires sufficient available referencing and/or monumentation. Additional consideration must be given to the location of the centerline or baseline, with respect to traffic conditions and physical impediments. Indirect alignment surveys are used where traffic conditions and physical impediments make occupation of the centerline or baseline impractical. Parallel baselines are used where sufficient referencing and monumentation is available and where conditions are uniform along the alignment. Random traversing is used where there is a lack of A.3-5 referencing and monumentation or where conditions are irregular along the alignment.
The assumed plane coordinate system (Cartesian) adopted will consist of arbitrary assignment of the 'X' and 'Y' grid axis values. The 'X' axis represents the eastings and the 'Y' axis represents the northings. The assumed values should not be coincident with the SPCS values and should be set to avoid transpositional errors in the 'X' and 'Y' (the range of 'X' and 'Y' values do not overlap). Orientation of the grid would be based on astronomical observation (or plan bearings if deemed appropriate).
Field procedures would provide accuracies stipulated for Third Order, Class II surveys. Checking the horizontal component of the survey for error of closure will be performed for Third Order, Class II surveys since closed traversing is required. Vertical leveling should be checked before proceeding. Other requirements are contained in Chapter 4 - Field Survey Procedures.
3.2 TWO - DIMENSIONAL SURVEYS
This classification of field surveys consists of establishing horizontal control with referenced monumentation. The type of project does not require changes in the vertical component (profile or cross sectional), therefore vertical control is not established. The existing roadway serves as the frame of reference for application of a typical section. Projects where the application of the typical section (resurfacing, reconstruction without widening, etc.) does not require volumetric computations (cut and fill) or slope staking would use this classification.
The requirements listed in Section 3.1.C - Assumed Plane Coordinates will be met (except the vertical control portion) for this classification. One minor variation of this survey classification would be checking cross slopes. This could be accomplished by determining the difference in elevation with a level (or locke level) and dividing by the distance.
3.3 ONE - DIMENSIONAL SURVEYS (FLATCHAIN SURVEYS)
This classification of field surveys consists of establishing the existing roadway stations. Since there is no control, there is no requirement for referencing. Resurfacing, maintenance, and minor improvement projects would use this type of survey. Plans developed from this survey would be straight strip without changes in horizontal.
The required accuracy for this survey is listed in Chapter 1 - Measurements and Computations. Topography taken as part of this survey would be by the plus and offset method using the centerline of the existing roadway as the frame of reference. A.4-1
CHAPTER 4
FIELD SURVEY PROCEDURES
4.0 INTRODUCTION
Procedures and requirements outlined in this chapter imply application to preliminary route surveys as outlined in Part A, Chapter 6 - Survey Types. However, these procedures and requirements apply to all other survey types with consideration of requirements specific to the performance of the work.
Survey procedures are described for both conventional (transit and chain) and total station, since both methods are used. The primary difference between these two methods is in the field book entries required to document observed measurements. Requirements for the field books are outlined in Part A, Chapter 7 - Field Book Compilation, Format, and Recordings.
Performance of quality field surveys begins with proper planning and information gathering. Survey requirements must be developed to provide the necessary database for plan preparation, design and construction. Horizontal control reference data, bench mark locations and elevations, as-built plans, location maps, US Geological Survey (USGS) Quad Maps, etc. must be obtained prior to start of work. Decisions to stake the alignment or run random control traverses; establish State Plane Coordinate System (SPCS) ties or use assumed coordinates or no coordinates; establish vertical control from bench marks or use assumed elevations or no elevations must be made and all of the supporting information obtained prior to the start of actual field work. A meeting should be held between the designer and surveyor well in advance of the surveys to ensure that the planning and information gathering phase is properly addressed.
Several other pre-survey activities need to be addressed prior to the actual start of field work. Surveying activities beyond the existing legal right-of-way require that letters of intent to enter be sent 10 days prior to the start of work. Current procedures and format requirements are outlined in DM-1A, page 6-12. Surveys on private property must be conducted in a courteous, professional manner since the surveyors are Department representatives.
Surveys on railroad operating right-of-ways require right-of-entry agreements, and, in certain circumstances, the presence of a railroad flagman is required. The Department has statewide agreements in place with many operating railroads for Department survey crews. Surveyors are to attend yearly training as offered by the railroad community. Consultants must obtain their own right-of-entry and flagman services for their survey activities. Advance coordination and scheduling is important to ensure that right-of-entry and services of a railroad flagman are obtained prior to field operations.
Traffic control is an extremely important consideration in planning and execution of field surveys along highways. Safety and protection of the surveyor and traveling public must not be overlooked. Work adjacent to the traveled way must be "signed" in accordance with A.4-2
Publication 213, "Short Term WZTC Guide" (Publication 213). Additional consideration must be given to the use of traffic cones to highlight the survey party; placement of a protective vehicle with flashing amber warning light(s); and the use of a flagman to get the motorists attention as well as keep a watchful eye on other members of the survey party. When it is necessary to occupy the traveled way, short term traffic control for work zones as outlined in Publication 213, "Work Zone Traffic Control" for the various types of highways and locations (inside lanes, outside lanes, etc.) must be followed.
Field survey procedures in the following sections outline normal requirements for various field operations. In general, the procedures will accommodate most of projects for which field surveys are required. However, circumstances will inevitably arise for which these procedures would not produce the required results. Requirements would have to be developed for these projects in consultation with the District Survey Manager.
4.1 CONTROL TRAVERSES
Control traverses are used for a number of reasons on highway route surveys. As discussed in Part A, Chapter 3 - Field Survey Classifications, control traverses are used to establish horizontal and vertical control for three-dimensional surveys. Random control traverses are used with increasing frequency with the advent of electronic total station surveying equipment and CADD based plan preparation. Electronic total station surveying equipment with random control traverse provides a safer environment for the survey party, since direct occupation of the centerline / baseline is unnecessary and the instrument is located adjacent to the roadway.
Electronic data collectors provide a rapid means of collecting, storing, and transferring data to the CADD workstation. CADD provides an efficient means of displaying the topography, fitting the alignment, reconciling alignment misfit, and establishing coordinate geometry. There is an important degree of interaction between surveys and CADD based design which must be considered in the work flow process. Interaction between the surveyor and designer is essential for effective execution of field and office activities. A discussion of this relationship can be found in Part A, Chapter 5 - Office CADD Procedures.
Control traversing for geodetic and SPCS based projects must meet requirements outlined in Chapter 3 - Field Survey Classifications, Section 3.1 - Three-Dimensional Surveys. Space control traverse stations at 1000 feet (300 m) maximum interval spacing within the project limits and as required elsewhere. Stations will consist of hubs with tack or 24 in. (600 mm) steel reinforcement bars on open ground, PK or Mag nails on bituminous pavement, drill holes on concrete, or other methods as appropriate to the circumstances. The distance between Referencing and monumentation will be in accordance with requirements in Section 4.3, page A.4-4 - Reference Monumentation.
Control traverse procedures will consist of using tripod based targeting and prism setup on all angle and distance observations. Proper tripod setup procedures with base plate and optical plummets must be followed to attain required accuracy. The use of prism poles or plumb sighting is not allowed. A.4-3
Astronomical azimuths will consist of observation of Polaris for geodetic and SPCS traversing and sun shots for assumed plane coordinate traversing. Sun shots may be used on SPCS traversing for azimuth checking provided that unadjusted closure in position of the traverse exceeds minimum accuracy requirements outlined in Table 1.3.1, Part A, Chapter 1, page 1-11. Sun shots may also be used to establish starting or ending azimuths when occupying SPCS reference monuments where other reference monuments are either destroyed or not visible. Whenever sun shots are employed to establish or check azimuth it is very important to follow procedures carefully. If the sun shot observations fail to meet accuracy requirements (standard deviation of mean or rejection limit and azimuth closure), then observation of Polaris will be required. Perform and note accuracy checks in the field book during the traverse survey. Any deviation from accuracy requirements will require reoccupation of the control traverse station and new (acceptable) observation entries in the field book. Perform traverse closure computations for all closed traverses before proceeding with additional surveys to ensure that closure meets accuracy requirements. Many methods are available for traverse closure adjustment computations. The least squares method is becoming increasingly popular with the advent of the personal computer. However, the compass rule will also produce acceptable results if azimuths are adjusted to astronomical azimuths prior to performing the computation. Closed loop traverses should also be checked for geometric closure by summing the interior angles and comparing the observed value with the absolute sum.
Geodetic and SPCS control would normally consist of end point closed traversing. These control traverses would be the primary control baselines. Control on assumed coordinates would consist of closed traversing. However, there are situations on projects which will require secondary control traverses - dual, parallel (random) primary control baselines; interchange perimeter control baselines; baselines for topography would represent some of these situations. Requirements outlined for primary control baselines would also apply to these secondary control traverses.
4.2 CENTERLINE
The centerline will be established in the field if required for the project. The term centerline includes baselines when referencing to alignment on directional single lane ramps or four-lane bifurcated highways. The decision to set centerline controls and/or stake the stations must consider the need and whether conditions of the project are conducive to this work. Need would be based on field survey classification, acquisition of right-of-way or other field activities such as field views and other survey procedures. Conditions to consider would include volume and speed of traffic, available working space, and physical impediments such as concrete and metal barrier.
When required, centerlines for the mainline, ramps, side roads, and other roadways will be set in the field at 50 feet (20 m) station intervals. 50 feet (20 m) station intervals will be used for curves over 300 feet (100 m) radius. For curves equal to or less than 300 feet (100 m) radius, use 25 feet (10 m) station intervals. Control points such as POT's, PI's, POST's, PC's, PT's, POC's, TS's, SC's, CS's, ST's, and Spiral PI's will also be set. Referencing and monumentation of alignment control will be as outlined in Section 4.3 - Reference Monumentation. A.4-4
Centerline staking will meet the following requirements for the various surfaces encountered along the alignments: 50 ft (20 m) Control Witness Stations Points Marking Open Ground - 6 in. spike w/red 24 in. (600 mm) Guard with flagging or Reinforcement Bar Black Marker Hub & Tack
Bituminous Pavement - PK Mag Nail PK Mag Nail White Paint
Concrete Pavement - Drill Hole Drill Hole White Paint or Cross Cut or Cross Cut
Witness markings will contain the full description of the centerline alignment control points being marked. Examples: PC STA 964+87.92 (29+409.517); EQ PT STA 983+41.59 (29+974.517) BK = POT STA 983+41.61 (29+974.523) AHD; and POC STA 983+99.00 (29+992.017). Interval station markings would follow full and intermediate designations as follows: 965+00 (29+500) 5+50 (+520) 6+00 (+540) 6+50 (+560) 7+00 (+580) 7+50 (29+600) etc.
On open ground, place the witness marker within 2 feet (0.5 m) of the control point and interval station with the flat side showing the station description toward the centerline staked point and paint the station description within 2 feet (0.5 m) of the point on bituminous and concrete pavements.
For those projects requiring stationing for field views or other survey activities, but where conditions preclude staking the alignment directly, station designations may be painted along the outside shoulder perpendicular to the actual station locations. This can be accomplished along equivalent parallel baselines or random control traverses (after computing and fitting the alignment) by flat chaining the interval stations. Care should be exercised during flat chaining to ensure that the effect of slope and horizontal curvature (shortening or lengthening of chords) are considered.
Right of Way and Construction Centerline/Baseline Definitions: General: Centerline – Alignment that most nearly follows the center of traveled portion of roadway Baseline - Line used to perform work and/or used to describe legal and/or required right of way and normally is not in the center of traveled portion of roadway. Survey – the inclusion of survey data in describing alignment implies the alignment was “ran in” or staked in the field. A.4-5
Plan Types versus Alignment Types: The alignment label to use will be dependent upon the Plan being prepared. Right of Way (R/W) Plan – use Survey and R/W centerline, Survey and R/W Baseline, Survey, R/W and Construction Centerline, and Survey R/W and Construction Baseline (Construction Centerline or Baseline shown if different than Right of Way Centerline/Baseline). Legal Right of Way Centerline, Legal Right of Way Baseline, Required Right of Way Centerline, and Required Right of Way Baseline are acceptable alternatives on a Right of Way Plan. Construction Plan – Construction Centerline and/or Construction Baseline. Combination Right of Way and Construction Plan - Survey, R/W, and Construction Centerline and/or Baseline and/or any of these combined. Types of Alignments: 1) Survey Centerline – Same as Legal Right of Way Centerline and is the best fit alignment to existing Right of Way plans as field surveyed. 2) Survey Baseline- A working baseline that is used in the field and may or may not coincide with Right of Way Centerline. 3) Right of Way Centerline – On Right of Way plans, this is the centerline where the Required Right of Way was obtained. On construction plans, this is the new legal Right of Way line. 4) Right of Way Baseline - On Right of Way plans, this is the baseline that the Required Right of Way is taken from. On Construction plan, this is the new Legal Right of Way line. 5) Construction Centerline - This is the centerline that the project is built from and may not coincide with the survey centerline. Usually these are on Two Lane Two Directional Roadways and/or Four Lane Divided Roadways with median. 6) Construction Baselines- This is a baseline that the project or parts of project are built from and may not coincide with survey centerline/baseline. Usually these are on Four Lane Divided Highways with a large Median or gore areas and access ramps, examples are I-80, I-81, I-79. 7) Legal Right of Way Centerline – Same as Survey Centerline. 8) Legal Right of Way Baseline – Baseline for Existing Right of Way. 9) Required Right of Way Centerline – Same as Right of Way Centerline. 10) Required Right of Way Baseline – Same as Right of Way Baseline. Note: It is possible to see a Survey Centerline and Right of Way Centerline on a plan if the Required Right of Way is not coincident with existing alignment and the geometry is different. All Centerlines or Baselines will adhere to the following text styles: Slanted Text = Existing, Normal Text = Proposed.
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Examples of Different Centerlines and Baselines
Figure 4.2.1 Right of Way Plan 4 Lane Divided and Ramps
Figure 4.2.2 Combination Right of Way and Construction Plan
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Figure 4.2.3 Right of Way Plan Legal on Left and Required on Right Both sides referenced to Right of Way Baseline
Figure 4.2.4 Right of Way Plan A.4-8
Figure 4.2.5 Right of Way Plan Multiple Baselines
Figure 4.2.6 Right of Way Plan Single Baseline
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Figure 4.2.7 Right of Way Plan 4 Lanes Survey and R/Way Baselines Different Geometry
Figure 4.2.8 Right of Way Plan Legal R/W Baseline and Combination Survey, R/W, and Construction Centerline
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Figure 4.2.9 Right of Way Plan Two Centerlines
4.3 REFERENCE MONUMENTATION
Sufficient centerline control points will be permanently referenced with 24 in. (600 mm), NO 5 or natural or man made features to insure future recovery of the centerline before and after construction is completed. The intervals between permanently referenced points will vary depending on the class of highway, but normally should not exceed 1000 feet (300 m) for most roadway conditions and not more than 5000 feet (1500 m) on long sight distance type roadways.
Reference monumentation procedure is as follows: For curves 1000 feet (300 m) or longer, both the PC and PT will be permanently referenced. On tangent sections, POT's will be permanently referenced at intervals not to exceed 1000 feet (300 m) on most roadways and not more than 5000 feet (1500 m) on highways having long sight distances. At least one permanently referenced POT must be visible from each permanently A.4-11
referenced PC or PT. These pairs of adjacent permanently referenced points will enable the centerline to be reestablished.
Control traverse stations will be permanently set, as specified in Section 4.1 - Control Traverses, and will be referenced using the swing-tie method. Intermediate traverse stations will be marked with 12 in. (300 mm) spikes or hubs. Swing-tie references for intermediate traverse stations are optional.
Centerline control points, as specified in Section 4.2 - Centerline, will be accurately and permanently referenced. Referencing will be performed by using the method as shown in DM3, Fig. 2.13. Alternate referencing may only be used at the discretion of the District Survey Manager.
With the angle and distance method the control point will be referenced to a minimum of three (3) permanent buildings or structures outside limits of construction and on either side of the centerline at a distance from the control point referenced no greater than 100 feet (30 m). Reinforcement bars will be set if no permanent objects can be used. Angle measurements will be recorded to the nearest 1 second. Distance measurements will be recorded to the nearest 0.01 foot (1 mm) and coordinate value will be provided on the three reference points. In selecting permanent objects and/or setting reinforcement bars for referencing, care must be exercised to insure that the centerline point can be reestablished by direct or offset occupation of not less than two (2) reference points, each having backsights and foresights of sufficient length and angular separation to accurately determine the location of the centerline point.
Permanent witness marks will not be placed at references set for recovering centerline control points.
Reference monumentation requirements for right-of-way purposes include the following: On major projects, the required right-of-way line will be marked with hubs and tacks or 1000 feet (300 m) spikes at all break points unless directed otherwise by the District Survey Manager.
After right-of-way acquisition and prior to construction, designated break points and/or other points on the right-of-way line will be permanently monumented with 24 inch (0.6 m), # 5 steel reinforcement bar with plastic cap or other cap suitable for center punching.
The right-of-way line will be monumented at locations as directed by the District Survey Manager but not normally closer than 500 feet (150 m) or further than 1000 feet (300 m) apart. The District Survey Manager will review and approve monumentation to be placed by consultants.
Designation of points to be monumented will provide for a direct line of sight to another monumented right-of-way point on either side of the highway, or to a monument referencing the centerline. This procedure will provide a starting bearing for future survey work by the Department or others.
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The monumented right-of-way points and monumented references for centerline control points will complement each other, and not result in redundant excessive points.
Permanent witness marks will not be placed at permanently monumented right-of- way points.
4.4 TOPOGRAPHY
This work should be simplified as much as possible. Topography is recorded after all horizontal alignment is established and stations are marked for conventional survey procedures and after the control traverse is set for total station surveys. All physical features, which affect the proposed design, will be recorded.
Detailed description will include utility names and pole ID numbers, signs (type and description), guide rail (types and end treatment), drainage (size and types), existing property corners and physical lines of property possession, permanent buildings (including type of structure), all permanent improvements constructed by the occupier of the property and traffic line patterns. Also see Appendix D for Quality Assurance/Quality Control Checklist for Right of Way and Construction Plans.
Procedures are described for both conventional and total station, since both methods are used. The preliminary difference between these two methods is in the field book entries required to document the observed measurements. Requirements for field books are outlined in Part A. Chapter 7 - Field Book Compilation, Format, and Recordings.
A. Conventional Method. Topographic features are recorded by noting the "plus" distance along the centerline from the last full station and the right angle "offset" distance located from the centerline to the object. A right angle prism or a mirror will be used to assure the point on the centerline is at a right angle to the object. In addition, topographic features will be recorded at radial offset distances along curves. A separate field book for all topography notes may be required. Stations will be labeled with an "x" on a vertical line, which represents the roadway centerline. These stations will be recorded in ascending order from the bottom of the page to the top of the page. A straight line in the field book will be used to represent a horizontal curve. All curve data will be shown in the alignment field book. Field book entry format is further detailed in Part A, Chapter 7 - Field Book Compilation, Format, and Recordings. All physical features, which affect the proposed design, will be recorded. Pole lines and fences will be located on tangents, by giving station "pluses" and "offset" distances to face of poles or fence points nearest the roadway, and at such intermediate points where there may be a break in the line of poles or fence. Intermediate poles in a straight line will be located by station "pluses" only. On curves, the type and size of poles will be located by individual station "pluses" and "offset" distances. Edges of traveled roadway will be located by "offset" distances from all centerline stakes and from any intermediate breaks in line of the traveled way. In heavy cuts and hillside sections, the edge of ditch or bottom of cut and top of embankment will be located in the same manner as the traveled way.
Buildings with surrounding appurtenances will be located as complete as practical. Additional sketches with dimensions may be required to fully describe the building layout A.4-13
and features. All structures and public utilities will be located and recorded. Public utilities include, but are not limited to, storm and sanitary sewers, water and gas mains, water and gas valves, and electric conduits and poles. Location of overhead utility lines will be recorded with the ownership and elevation to the low wire. Indirect methods, such as vertical angle and distance, will be used to determine the height of the utility line as the use of a rod or a tape is dangerous with live electric lines. Additional topographic information includes curbs, sidewalks, and building lines.
County, township, borough, and other legal subdivision lines will be located where practical using station "pluses" and angle of intersection with the centerline. The angle of intersection with the centerline will be determined. All utilities, such as railroads, railways, pipelines, and pole lines will also be accurately located and recorded with the names and owners if available.
Complete data will be secured for all culverts; the location, skew, size, length, and other important dimensions will be carefully recorded for each.
B. Total Station. Topographic features, such as horizontal and vertical distances, station coordinates, and elevations are automatically measured, processed, and recorded as part of a total station setup. All electronic data may be stored in the collector and may be directly input into an office microcomputer. This information may then be shown graphically through a plotter.
Radial topography will be performed and noted in the field books as outlined in Part A. Chapter 7 - Field Book Compilation, Format, and Recordings. These field book entries include height of instrument, prism height, instrument location, backsight location, and foresight location. The foresight location will include horizontal angle, distance (if not horizontal, a vertical angle will be recorded), and description. A backsight reading to verify a previously established control point will also be recorded in the field book. Sketches will be required for any figures shown such as buildings, sidewalks, fences, etc. Single point locations, such as fire hydrants, signs, poles, etc., will not be required on the sketch. All instrument locations and backsight locations will be points that were previously shown in the alignment or traverse notes.
Upon approval of the District Survey Manager, a hard copy printout of data collector information may be filed with the field book. This printout could replace some of the field book entries, such as angle and distance. Approval will be considered only after a sample printout has been submitted.
4.5 CROSS SECTIONS/PROFILES
Cross section and profile surveys will be undertaken as part of conventional survey work as outlined in Section 4.5.A - Cross Sections and in Section 4.5.B - Profiles. Total station survey requirements would be conducted as part of the topographic surveys as outlined in Section 4.5.C - Total Station. It is important to recognize that certain project conditions may result in a combination of survey methods.
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A. Cross Sections. Cross sections are taken after horizontal and vertical controls have been established. A cross section is a vertical section of the surface of the ground taken perpendicular to the centerline. In addition, readings are taken at locations where there is a change in the terrain.
Cross section data is gathered at a maximum of 50 feet (20 m) intervals and at the requested offset distances perpendicular to the centerline of the project. Additional cross sections will be taken and construction grades will be established in areas where heavy grading is deemed advisable to reduce steep grades or to secure the necessary width in heavy cuts. Offset and elevation readings are then recorded at all locations (including any breaks in the terrain). Cross section data will extend beyond the proposed right-of-way line.
To begin cross sectioning, differential levels are run from the nearest benchmark to the part of the line to be cross-sectioned. The instrument should be set up under normal conditions to read 2 or 3 stations back and ahead of each set up. Great care must be taken in the selection of the instrument location so that all, or nearly all, of the necessary readings can be obtained.
Elevations should be checked with all available benchmarks and should close within 0.05 foot ( 10 mm).
Rod readings will be taken at all breaks. Existing pavement elevations are recorded to the nearest 0.01 foot (1 mm) and natural ground elevations are recorded to the nearest 0.05 foot (10 mm). Distances to culvert endwalls, pavement edges, and ground shots should be carefully measured and recorded to the nearest 0.05 foot (10 mm). Those points must be on a line perpendicular to the centerline unless otherwise noted. Special care must be taken to keep the shots at right angles when cross sections extend out beyond 50 feet (15 m).
Cross section data are recorded in notes opposite the station number in fractional form with the rod reading as the denominator and distance from centerline as the numerator. Care must be taken to record readings correctly as to left or right of the centerline. The proper method of recording cross section notes is further described in Part A, Chapter 7 - Field Book Compilation, Format, and Recordings.
At railroad and railway crossings, elevations and cross sections will be taken as outlined under Part A, Chapter 6 - Survey Types, Section 6.1 - Preliminary Surveys. Where a railroad or railway parallels the proposed alignment and within a distance that may be affected by the proposed construction, the tracks and structures will be located, the roadway cross sections will be extended, and the cross sections will be taken.
B. Profiles. Benchmarks will be established in the standard manner to the nearest 0.01 foot (1 mm). Profile readings for existing pavement elevations will be recorded to the nearest 0.01 foot (1 mm) for all centerline points at stations and intermediate breaks. Readings will be taken and recorded to the nearest 0.01 foot (1 mm) for tops of all offset stakes and to the nearest 0.1 foot (10 mm) for ground elevations at stakes. Elevations will be taken of flow lines of pipes and small culverts and profiles of the ground or stream line extended for a distance of at least 50 feet (15 m) beyond each end of the pipe or culvert. A.4-15
Profiles will be taken at low points or at other advisable locations in like manner, if no culvert exists at present. Profiles will be plotted to facilitate the establishment and correct location of drainage structures and ditches.
At intersecting roadways and drives, profile elevations will be taken for such distances as may be affected by construction.
C. Total Station. Cross sections and profiles would be taken during the topography surveys. Ground shots with breaks in the ground, pavement, and shoulders would be obtained with appropriate coding of the data. Backsight readings to verify previously established control points will also be provided. The shot frequency, or density, would be sufficient to accurately create a 3D model and cut cross sections and profiles in the office as part of the CADD design. The surveyor and designer must understand the individual project requirements prior to undertaking the fieldwork.
4.6 BENCH LEVELS
Running the initial bench level circuit is often conducted when establishing horizontal alignment. A previously established benchmark in the vicinity of the project site is required to begin the bench level circuit. This benchmark may be an official monument established by a federal, state, or county agency or it may be established by GPS observation. The published source or method used to obtain the beginning benchmark must be noted in project field book. The leveling instrument (as discussed in Part A, Chapter 2 - Surveying Equipment and Supplies, Section 2.2 – Vertical Measurement Equipment) will be set up at a distance where the benchmark can clearly be observed. It is preferable to set up the instrument to within maximum distances established in Table 1.3.2, Part A, Chapter 1, page A.1-12. A level rod is then placed on the benchmark to establish the "+" value. The "HI" value is then computed by adding the bench mark elevation to the newly established "+" value. A turning point will then be set at approximately the same distance away from the instrument as the benchmark. Trigonometric or barometric leveling is not allowed. Benchmarks must be placed on permanent structures or objects (i.e. bridge abutments, inlet headwalls, traffic signal bases) or constructed as permanent concrete monuments. Temporary benchmarks may be placed on spikes in trees or utility poles, or on fire hydrants. The practice of using PK™ or Mag™ nails or reinforcement (rebar) pins is to be discouraged. The minimum recommended distance between benchmarks on a PennDOT project is 1000 feet (300 m). Deviation from the above is at the discretion of the District Survey Manager.
4.7 QUALITY CONTROL
All survey measurement equipment is designed and constructed in a manner to provide correct horizontal and vertical measurements. However, variations in measurement readings may occur as a result of temperature changes, mechanical (electrical) failure, or poor handling of the instrument during the survey recordings. Therefore, all survey measurement equipment will be checked and calibrated on a routine basis.
All equipment should be checked every 6 months and/or at the beginning of a long duration A.4-16 project. There are currently 11 locations in Pennsylvania from which the electronic distance measuring instruments (EDMI) can be calibrated. Information on these locations is compiled and published by the National Oceanic and Atmospheric Administration, National Geodetic Survey (NGS). The procedures established to adjust survey equipment are outlined in Part A, Chapter 2 - Surveying Equipment and Supplies, Section 2.4 - Calibration of Equipment. Double pegging levels periodically would also assure that drift in precision is minimized.
In addition to the adjustments required for survey equipment, proper field survey procedures will also provide for higher accuracy measurement recordings. For instance, when performing a bench level circuit, both the foresight and backsight distances should be approximately the same. Other field survey procedures that are essential to perform accurate work are outlined in this chapter.
Another means to analyze field data from total station surveys from a quality control perspective is through the use of "test" surveys. A "test" survey run with conventional methods may be conducted on a portion of a project to determine the accuracy of cross- section or profile information. The District Survey Manager will determine the need for and requirements of a test survey for each specific situation. A.5-1
CHAPTER 5
TRANSFERRING SURVEY DATA TO CADD
5.0 INTRODUCTION
The Department's electronic data collection equipment provides a means of collecting, storing, and transferring survey data to the Computer Aided Drafting and Design (CADD) system. The CADD system provides the means to convert the data into forms that can be used as the basis for the highway and / or structure design. The connection between the data collector and CADD system necessitates good cooperation between the surveyor and designer. An outline of this relationship can be found in Section 5.1- Survey Procedures.
5.1 SURVEY PROCEDURES
This section provides a brief outline of the procedures that will be followed when collecting and transferring survey data from the electronic data collector to the CADD system. The steps, in general, are:
• Collect survey data using an electronic data collector.
• Transfer collected data to the CADD system.
• Process raw survey data into design data.
• Transfer data to the design squad.
• Verify integrity of the data.
• Proceed with design.
Interface procedures between an electronic data collector and an Intergraph surveying software package are described in complete detail in the document entitled "Survey Software Users Manual", which can be obtained by the District Survey Manager.
Interface procedures between an electronic data collector and other survey software packages used by consultants may be obtained from the specific software manufacturer.
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CHAPTER 6
SURVEY TYPES
6.0 INTRODUCTION
This chapter outlines the standard requirements and procedures for the various survey types. Each survey type described will be conducted in order to provide the most accurate data attainable for that specific task. These survey types will be referenced to Part A, Chapter 4 - Field Survey Procedures to gain a greater understanding of various procedures performed in the field.
Before beginning any survey, a "Notice of Intent to Enter" (R/W983) will be prepared and mailed to any impacted property owners. This notice will alert the property owner that PennDOT employees, their consultants, and/or their contractors may need to enter their land in order to conduct surveys. The specific requirements are outlined in Section 409 of the "Eminent Domain Code", dated September 1, 1964. All policies and procedures will be in accordance with Design Manual, Part 1.
Other pre-survey activities, such as right-of-entry agreements on railroad properties and traffic control considerations along the highway system, are outlined in Part A, Chapter 4 - Field Survey Procedures.
6.1 PRELIMINARY SURVEYS
Preliminary surveys are primarily performed for all types of design and construction projects. These type projects include resurfacing, restoration, and rehabilitation projects; and realignment, widening, relocating, and reconstruction projects. These surveys are performed to secure complete and accurate data necessary for the design and preparation of construction drawings for highways and structures.
Part A, Chapter 3 - Field Survey Classifications contains a complete description of the three classifications of field surveys. Three-dimensional, two-dimensional, and one-dimensional surveys are all used for preliminary surveys. Each has a use for the complexity or specific project, design of construction requirements anticipated.
A. Requirements. All distance measurements and elevations will be read and recorded to the values outlined in Part A, Chapter 4 - Field Survey Procedures. The following is a minimum list of items to be located: Edge of road and edge of shoulder locations at specified intervals. Traffic paint line patterns. Traffic and advertising signs within specified limits. Utility poles and guy wires. Guide rail type and location at specified intervals. Median barriers and traffic separation islands. Curbs and sidewalks. A.6-2
Drainage inlets and end walls. Manhole covers. Water main valves. Trees, shrubs, and bushes within specified limits. Pavement joints. Stream and railroad structures. Railroad crossings. Intersecting streets and driveways, including widths and types. Any other topography within the specific limits which may interfere with grading, construction, or paving operations.
B. Procedures. A control traverse for three-dimensional surveys will be established as outlined in Part A, Chapter 4 - Field Survey Procedures, Section 4.1 - Control Traverses. After closing and balancing the traverse, the ties to the final centerline will be calculated. Stations will then be established at 50 feet (20 m) intervals along the final centerline. Bench levels will be established and checked throughout the project at 1000 feet (300 m) intervals. All topography will be recorded. All cross-sectional information will be recorded at 50 feet (20 m) intervals. All control points (PC's, PT's, POC's, and POT's) will be referenced to at least three (3) permanent objects beyond the limits of construction.
Three-dimensional surveys with random or parallel control traverse baselines, where the centerline cannot be occupied, would proceed in much the same manner, except that the alignment would not be staked.
6.2 BRIDGE SURVEYS/WETLAND LOCATION SURVEYS/ HYDROLOGIC SURVEYS
Bridge site surveys are performed to obtain accurate data required for the design of a new structure or for the rehabilitation of an existing structure.
A. Requirements. Following are items to be included with the survey and should be expanded as required:
Name of stream or branch, intersecting roadway or railroad. Direction of flow, number of lanes or tracks. Number and length of spans. Clear width between roadway curbs and wheel guards. Clear width between parapets, girders, trusses, and hand rails. Width of sidewalks. Type and general condition of superstructure. General condition of abutments, piers, wings, etc. Minimum vertical clearance and location.
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B. Procedures. The roadway centerline will be established 1000 feet (300 m) to either side of the crossing. At the crossing, a control point will be established on the roadway centerline from which a stream reference baseline will be developed. The plus (+) at the point of intersection between the roadway centerline and the stream reference baseline, as well as the angle between the roadway centerline and the stream reference baseline, will be recorded. The stream reference baseline will be extended for a minimum of 500 feet (150 m) in both the upstream and the downstream directions. The stream reference baseline will be located parallel to the stream to ensure that all cross-sections will be taken perpendicular to the stream. From the stream reference baseline, offsets to the stream edges will be taken at 50 feet (20 m) intervals or less and recorded. The result of these notes will give an accurate plot of the stream for at least 500 feet (150 m) on each side of the roadway centerline.
Grade separations will be handled in the same manner, but the reference baseline should be developed for a minimum of 100 feet (30 m) to each side of the roadway centerline.
All measurements and angles will be tied into the highway survey centerline.
At least one benchmark will be established on each side of an approved structure site. The location for each benchmark will be easily accessible for both preliminary surveys and final surveys. In addition, these benchmarks will be used to obtain all cross-section information for the structure and/or roadway.
Topography will be taken in detail within a reasonable area of each site so that all existing conditions that may affect the structure layout or design are noted.
Sufficient data will be obtained so that the adequacy (or inadequacy) of an existing structure to handle highway traffic, volumes, loads, or flood discharge can be determined. The waterway opening may be sufficient and the alignment for highway traffic satisfactory, but the roadway width may be too narrow. Certain types of bridges can economically be widened, decks replaced on existing substructures, and this should be given consideration. A meeting with the structural designer and the District Survey Manager should be conducted prior to the start of work to fully address the level of effort needed to produce the information needed to complete the bridge design. Measurements beyond standard topography, cross- sections, or bridge sketches for detailing superstructures and substructures; determining plumb, batter, or squareness; or special circumstances for unique structures must be determined early to ensure that the information is obtained in a timely and efficient manner.
Where a new structure over a stream is required, complete data should be obtained so that a proper waterway opening can be designed. All field data required concerning the design of the structure should also be obtained.
For the waterway design, the stream bed slope and the water surface slope should be obtained for a minimum distance of 500 feet (150 m) on each side of the bridge. If there is a dam or other similar structure within 1000 feet (300 m) range, its height, type, and any other physical details must be recorded. Maximum flood elevations and dates of occurrence will also be recorded. Flood information for the two highest known flood incidences will be recorded for A.6-4
all bridge spans 100 feet (30 m) or greater. The angle between the stream and the highway centerline will also be recorded.
For a proposed structure over or under a highway or railroad, cross-sections will be taken at 10 feet (3 m) intervals along both centerlines. For a proposed structure over a stream, cross-sections will be taken at 30 feet (10 m) intervals for a sufficient distance up and down the stream. All cross-section data will be carried across and at least up to the elevation of the 100-year floodplain. All evidence of erosion, scour, or debris accumulated will be recorded.
Sufficient data for potential channel relocations will be required so that the proposed channel section efficiency can be computed. In addition, all data pertaining to a retaining wall or to a fill located within the lines of the existing 100-year flood plane will be obtained. This information can then be used to determine the impact of these obstructions on the floodplain. Cross-sections will be carried for the full width of the existing channel, including overflow channel, and at least up to the 100-year floodplain elevation.
6.3 CONSTRUCTION SURVEYS
Construction surveys are performed to reestablish the centerline and provide the contractor with stakes from which the location and elevation of the new highway and/or structure can be determined. The requirements and procedures for the six construction survey types are as follows:
A. Type A. Type A construction surveys are used for new projects and are based on precise horizontal and vertical geometry. Horizontal and vertical control is established using 1” = 20’ (1:250) scale or 1” = 40’ (1:500) scale topographic mapping referenced to the Pennsylvania State Plane Coordinate System.
Requirements. The centerline and/or baselines, side road and channel alignments, plan baselines, and interchange alignments will be established, on the ground, at 50 feet (20 m) intervals and at major control points. Centerlines and/or baselines will be established at 30 feet (10 m) intervals for curves equal to or less than 300 feet (100 m) radius. All major control points will be referenced and vertical benchmarks will be established at appropriate locations.
Where the finished grade is 5 feet (1.5 m) or more vertically above or below the existing grade, place an offset grade point with a guard stake at right angles to the centerline or baseline controlling the grade point(s), or at 90 degrees from the tangent to the curve, at each 50 feet (20 m) or 30 feet (10 m) station. Offset grade points from the intersection of the cross-section template and original ground. Mark guard stakes according to the rounding, station, offset right or left of centerline/baseline, and offset from the intersection of the template and original ground.
Establish a finished grade control line offset, parallel to the centerline or baseline, by setting grade points at 50 feet (20 m) intervals. Establish grade points at 30 feet (10 m) intervals for curves equal to or less than 300 feet (100 m) radius. A.6-5
B. Type B. Type B construction surveys are used for reconstruction type projects. This survey type will also be performed for any minor structure work. Horizontal and vertical control is based on as-built plan information. The horizontal and vertical geometry may be reproduced on the existing roadway using minimal realignment.
Requirements. The centerline and/or baselines and side road and channel alignments will be established at 50 feet (20 m) intervals and at major control points. Centerlines and/or baselines will be established at 25 feet (10 m) intervals for curves equal to or less than 300 feet (100 m) radius. Vertical benchmarks will be established at appropriate locations.
All baselines, grade lines, offset grade lines, parallel lines, traverse lines, and reference lines will be established to control construction operations.
C. Type B Modified. Type B Modified construction surveys are used for reconstruction type projects. The horizontal control is based on any of the following information: As-built plan horizontal geometry or horizontal geometry produced on the existing roadway. Random traverse baseline. Flat chain alignment along the center of the existing roadway. A combination of horizontal geometry, random traverse baseline, and flatchain alignment.
Vertical control is based on any of the following information: Plan profile or finish grade only. Cross-sections related to existing roadway section. Produced baseline grades. Templates based on existing roadway cross-sections. Requirements. Centerline and/or baselines will be established at 50 feet (20 m) intervals and at major control points. Centerlines and/or baselines will be established at 3 feet (10 m) intervals for curves equal to or less than 300 feet (100 m) radius. Vertical control will be established at appropriate locations. All grade points, guard stakes, nails, hubs, or paint marks will be established to control construction operations.
The plan alignment and grade will be established for temporary roadways and crossovers.
The staking of legal right-of-way lines or temporary easement lines will be controlled by the horizontal geometry based on plan data.
D. Type C. Type C construction surveys are used for general maintenance, construction type projects. The survey is based on the existing roadway alignment with no established horizontal or vertical geometry. Flatchain stations or segment/offsets will be used as reference locations for all drawings and sketches.
Requirements. Flat chain surveying at 50 feet (20 m) intervals between the limits of work will be conducted to establish stationing and/or segment/offset information. Stations will be established along the centerline or along the edge of pavement with paint marks. However, A.6-6 placing stakes at right angles to the station or segment/offset is also acceptable. It should be noted that additional paint marks or stakes may be required to control construction operations.
E. Type D. Type D construction surveys are used for structure construction/replacement type projects. These projects consist of bridges, culverts, arches, and special structures. Horizontal and vertical control will be established by the Department. A Third Order, Class I survey and/or traverse network will be conducted at each structure site.
Requirements. Structure control points will be established along the centerline and/or baseline. All work points will be referenced. Three reference points are required for each work point located on an abutment or at the end of a wing wall. Three reference points will also be required for each work point established on any proprietary or other type wall. For land piers, three reference points will be established on each side of the substructure for each work point established on the centerline of bearing. The distance between the work point and its first reference point will be less than 100 feet (30 m). Baseline reference will be established for all water-bound piers.
A separate stake-out sketch will be prepared that includes centerline/baseline stations, span lengths, reference angles, reference lengths, and benchmark data. The date, structure number, structure type, contractor's name, and survey party chief's name will also be included with this stake-out sketch.
F. Type D Modified. Type D Modified construction surveys are used for structure rehabilitation type projects. These projects consist of bridges, culverts, and arches. Bridge rehabilitation may involve repair or replacement of part of the substructure, or all or part of the superstructure. Rehabilitation of an arch or culvert may involve the repair and/or the extension of the existing structure. Horizontal and vertical control will be established by the Department. Requirements. Structure control points will be established along the centerline and/or baseline. All work points will be referenced. Three reference points are required for each work point located on an abutment or at the end of a wing wall. For land piers, three reference points will be established on each side of the substructure for each work point established on the centerline of bearing. The distance between the work point and its first reference point will be less than 100 feet (30 m). Baseline reference will be established for all water-bound piers.
A separate stakeout sketch will be prepared that includes reference points, lengths, vertical control and any other pertinent plan data. In addition, either a sketch showing either a triangulation network or a traverse network, or a mathematical description supporting the methodology used to generate the survey will be prepared.
Stake-Out Sketch
(a) A stake-out sketch shall be shown, preferably on the first or second sheet of the structure drawings. There should be ample open space outside of the sketch to allow A.6-7
wing and barrier line extensions for stake point recordings. The sketch need not be to scale. Frequently, exaggerations of curvature, angle, etc., are necessary to show the information clearly.
(b) The sketch shall be as simple as possible, but as complete as possible so that the structures will be constructed according to the plans.
(c) All necessary tie-in dimensions between highway alignment, working points, lines of structure, and other control points shall be shown in millimeters (feet to two decimal places) on the sketch.
Stake-Out Guidelines
(a) The stake-out shall be referenced to one straight base line, except in the case of dual structures, where two straight base lines, properly referenced to each other, can be used. The base line will be the centerline of the highway (if tangent), or the long chord connecting the points where the centerline of the highway intersects the face of the abutments on a curved highway, or the tangent line at the point of intersection of highways or the highway and a stream or river. Generally, dimensioning along the long chord is preferred on sketches for viaducts with a long series of spans. In special situations, some other base line can be used if particularly convenient.
(b) The sketch shall show the base line and the shape of the exterior face of the substructure (abutments and wingwalls). All corners shall be referenced by showing work points and distances to the base line. Wingwall angles to the front face of abutments shall also be referenced. Work point coordinates may be shown on the plan.
(c) At intermediate piers, the skew angle between the centerline of the pier and the base line is required. The location of the intersection of pier centerline with base line shall be tied to other parts of the substructure by base line dimensions. The distance from the base line to the centerline of roadway along the centerline of the pier shall be given. The station of the intersection points at the base line shall be shown. Distances between the outside faces of each barrier shall be shown.
(d) For multi-level structures, each level shall be sketched separately, but referenced to the same base line.
(e) The stake-outs for box culverts shall include inside faces of walls, ends of the culvert, and the front face of the wingwalls. Reinforced concrete arch culverts and metal culverts shall be treated similarly.
Procedure to Ensure Against Discrepancies in Bridge Stake-Out
(a) The structure stake-out sketch and reference stake locations shall be recorded in a Department survey notebook.
(b) Original stake-out field notes shall be recorded in a survey notebook. When other copies are required, this information shall be taken from the original survey notebook.
(c) An error of closure on the stake-out shall be recorded in the survey notebook. This A.6-8
error of closure shall reflect a comparison between measured and computed angles and distances of a traverse around the near line of the offset stakes of all working lines and shall meet the minimum error of closure of 1:10,000 or a positional accuracy of 0.05 feet (0.02 m) plus 20 ppm for each offset point (see Figure 6.3.1).
(d) A complete centerline tie shall be made at the ends of a structure to ensure proper location.
Figure 6.3.1 - Bridge Stake-Out Closure
Run a closed traverse around the near line of offset stakes of all working lines. On projects where various phase stakeout is required, run the intermediate traverse as the stake-out progresses.
Upon completion of an acceptable closure of the perimeter traverse of 1:10,000, compute the individual closures between each pier of piers and abutment lines. These computations may be made in the field by the party Chief or in the office by a member of the District Bridge Unit.
Record this sketch and closure in a survey field book to be made readily available for inspection.
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G. Procedures. All distances will be read and recorded to within 0.03 foot (10 mm), except for the reference distances to the limit of project points. Reference points will be recorded to within 0.01 foot (1 mm). Bench levels will be run over the offset stakes to the nearest 0.01 foot (1 mm) and the elevations checked against the benchmarks throughout the project.
The construction survey field books will be prepared and the notes identified in accordance with Part A, Chapter 7 - Field Book Compilation, Format, and Recordings, Section 7.1 - Acceptance Requirements for Consultant Surveys. No changes will be made in the preliminary survey field books. However, any errors or discrepancies found in the preliminary survey notes, or on the drawings, will be noted in the preliminary and construction field books. When there has been an office change made on the drawings, the new line will be run in and, if necessary, new cross-sections will be taken. These changes will be incorporated in both the preliminary and construction survey field books.
The field books of the preliminary survey, drawings, and Special Provisions of the contract will be thoroughly reviewed by the survey party before beginning. The survey party will then locate original points of tangency and curvature on the ground from original notes. If any office changes appear on the drawings, they will be run in and the points of curvature and tangency staked and referenced to at least three permanent objects outside the construction area. The notes will indicate all relocation areas and their relation to the original centerline.
When alignment changes have been made, the centerline equation will be compared with that shown on the drawings. Either new cross-sections must be taken off the new alignment or the offset distance must be measured between the original centerline and the new alignment at the preliminary cross-section locations.
All reference points that have been, or will be, either disturbed or destroyed by the construction will be placed outside the construction area and will be properly described and noted in the field book. The construction centerline will be established over the entire project, if possible, before any work is done. This will enable the survey party chief and the inspector-in-charge to pick up a point on the centerline at any location and view the project as a whole before any work starts.
When the construction survey cannot be completed before the contractor starts operations, the inspector-in-charge will secure the contractor's plan of operation and the information as to where the contractor will commence operations. The survey party chief's work will be arranged to supply the contractor with sufficient stakes and information to ensure that the work will not be delayed.
Bench levels will be run and the benchmarks checked for location and elevation. Any benchmarks that have been destroyed or damaged, or that will be disturbed by new construction, will be reestablished or replaced in locations where they will not be disturbed. It will be the contractor's responsibility to record all information on reestablished benchmarks in the notes and to mark the set of plans used by the survey corps. Both the inspector-in-charge and the District will be informed of any bench mark changes by the contractor.
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Construction stakes are to be placed at right angles to the centerline on tangents and at radial offsets to the centerline on curves. Stakes set for slopes, limits of grading, etc. will be based on the offsets and elevations shown on the cross-sections. These construction stake locations are to be set at 50 feet (20 m) intervals and at all control points (PC's, PT's, POC's, and POT's).
For rough grade, the construction stakes will be referenced with three hubs and guards. The construction stakes will be established by driving a hub flush with the ground and by providing a guard stake behind the hub. (A hub protruding out of the ground is easily destroyed and subject to frost heave.) The guard stake will identify the station and offset of the construction stake from the centerline. The hub will have a transit tack placed in the top to denote the exact location of offset and elevation. For fine grade, the construction stakes will be referenced with a 12 in. (300 mm) spike driven flush with the ground.
Construction stakes will be placed beyond the limits of construction and inside the right-of- way. It is advisable to place the stakes on a parallel line on tangents, and possibly on curves, if the terrain and topographic features will not cause a costly delay in time.
Stakes will be placed at 30 feet (10 m) intervals or less at sharp horizontal curve locations (less than 300 feet (100 m) radius). On grades of more than four percent, an offset stake will be set on each side of each designated grade point. Slope stakes will be placed when the top of cut slopes or the toe of embankments are more than 5 feet (2 m) vertically above or below the finished grade line. The rounding of slopes in cut sections will be disregarded in the placing of slope stakes, and stakes will be placed at the intersection of the normal theoretical slope line with the present ground line. Limit of slope stakes will be placed for the rounding of slopes.
Stakes used on a construction survey will be placed well beyond the limits of construction, so the stakes can be referred to during construction and can be available for the final survey.
Bench levels will be run over these offset stakes to the nearest 0.01 foot (1 mm) and the elevations checked against the benchmarks throughout the project. All information will be recorded on the standard grade sheet, Form D-413. A copy of Form D-413 is provided as part of Appendix C - Standard Forms. The grade sheets will carry the proper identification at the top of Form D-413. The date prepared and the number of the field book from which the stake elevations and distances are copied will be included on Form D-413. The survey party chief will compute and check the stake elevations in the field and will forward the field book to the District immediately. The District will generally prepare the grade sheets. The District Survey Manager will determine the method of presentation and the responsibility for preparation of the grade sheets.
When the construction survey has been delayed and the contractor is working, it may be necessary for the survey party chief to prepare grade sheets in the field so as not to delay the contractor's operations. In this case, the survey party chief will prepare 3 copies of the grade sheets and have them checked by the inspector-in-charge. One copy will be given to the contractor, one copy to the inspector-in-charge, and one copy to the District. The A.6-11
District will also receive the field book. The District Survey Manager will prepare grade sheets in the regular manner and forward sufficient prints to the field with a letter advising the inspector-in-charge that the grade sheets prepared in the field were found correct. Any discrepancies found by the District Survey Manager will be noted and corrected immediately in the field.
When stakes are replaced in the field, the District Survey Manager will have new grade sheets prepared for the section affected and will forward all prints to the field. Any revisions to the grade sheets will be noted as "superseded" and will be dated accordingly. The inspector-in- charge will cross out, or void the data superseded on all copies of the original grade sheets.
Accurate cross-sections will be secured within the area of the proposed improvement before the contractor starts grading operations. If the cross-sections taken during the preliminary survey still show the true conditions, then they may be used without further work. However, if there has been any change in the contour of the ground surface, or if the original cross- sections were taken during the winter months and there is a general change due to frost or ice action, or if decided line changes have been made, then construction cross-sections will be taken before the contractor starts operations. The design may necessitate new or additional cross-sections. Care will be exercised in taking profiles and cross-sections where side roads and approaches are to be constructed. Additional cross-sections will be taken to include areas where structures, special ditches, or channel changes are made. Prints of construction cross- sections will be forwarded to the field as soon as possible.
Special structures will be staked well ahead of actual grading operations. This would enable the contractor to perform such work as building culverts, drains, sewers, and like structures as early as possible in order to obtain adequate settlement of the backfill. However, the survey corps will set stakes for large culverts, box culverts, channel changes, and all bridges.
US Coast and Geodetic Survey (USC&GS) benchmarks are established as a permanent record and extreme care will be exercised to preserve their value. If possible, they will not be disturbed until permission has been obtained. The contractor and the inspector-in-charge will immediately notified the District Survey Manager. Should the District Survey Manager decide that the USC&GS benchmark must be relocated, the District Survey Manager will make necessary arrangements to have the mark reset. The surveys to relocate these marks will be performed using methods and procedures as required to retain the accuracy of the original mark.
The centerline of the bridge will be staked. The stationing will be carried from locations established accurately at 50 feet (20 m) on either side of the bridge. The structure will be located as shown on the drawings and by using the bridge stakeout sheets furnished by the District. Work points will be located and referenced with sufficient ties established to the centerline. Figure 6.3.2 shows the suggested method of staking the bridge layout from the structure drawings. It should be noted that the dimensions of the bridge layout are shown to two (2) decimal places of a foot (three (3) decimal places of a meter). The original bridge layout from the structure drawings will provide hundredths of a foot (millimeter) dimensions for all measurements.
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Figure 6.3.2 Bridge Stake-Out
The establishment of the centerline and stationing of the structure will be checked by the District Survey Manager or the survey party chief in sufficient detail to verify its location. After work has started, the position cannot be adjusted without considerable cost and lost time. The centerline of the bridge will be monumented by driving hubs (outside of the construction area) at each side of the structure. When possible a backsight will be set on line so that, in case the sight is blocked over the structure by forms, the centerline can always be determined. These centerline hubs will always be tacked and referenced to objects that are not to be disturbed during the construction.
Face of abutments, centerline of piers, outside line of parapets, and other needed working lines, will be referenced by at least two stakes on each side of the bridge. The face line of wings will be run and referenced by at least two stakes. All stakes will be protected by the contractor in an approved manner. The line of the top of abutment will be staked when the face of abutment is battered. The location of all stakes will be shown on a sketch provided either in the notes or on a form furnished by the District.
The District bridge engineer will furnish the inspector-in-charge with all elevations and measurements necessary for construction of the structure.
Normally, on a spiral curve, it is advisable that the survey party chief refer to the tables and computations as given in either "Transition Curves for Highways" by Joseph Barnett or in "Route Location and Design" by Thomas F. Hickerson, published by the United States Printing Office and McGraw-Hill Book Company, respectively. However, if the spiral is designed in the office and placed on a plan as a construction centerline, it is easier to compute the offsets from the simple curve than establish the spiral on its own centerline. This is applicable to a simple curve with spirals at each end. First, establish the simple curve centerline followed by the TS, SC, CS, and ST.
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6.4 BORROW PIT SURVEYS
Borrow pit surveys are used to determine the amount of material removed from a certain location for use with new improvements to various construction projects.
A. Requirements. All distances will be read and recorded to within 0.05 foot (10 mm). Reference points for control baselines will be recorded to within .01 foot (1 mm). Bench levels will be run over the offset stakes to the nearest 0.05 foot (10 mm) and the elevations checked against benchmarks throughout the project.
B. Procedures. No borrow pit will be staked or cross-sectioned until the site and material has been approved by either the District Construction Engineer or the Assistant District Construction engineer. The approximate amount of borrow needed will be determined prior to the staking in order to determine the approximate limits of the borrow pit. The site of the borrow pit must be cleared, grubbed, and stripped of all sod and other unsuitable materials before cross-sections are taken.
In staking borrow pits, a baseline will be established well outside the borrow limits. Stakes will be driven flush with the ground and protected by guard stakes so that they will not be disturbed until after the final cross-sections are taken. These stakes will be placed at each point where the contour of the ground changes. All stakes will be placed at a maximum of 50 feet (20 m) apart. A second baseline will then be established, running opposite, and parallel to the original, and well beyond the limits of the proposed borrow pit. The borrow pit will lie between these two baselines. This second baseline will then be staked so that each stake will be directly opposite the corresponding stake on the original baseline. These baselines will be straight and without any angles or turns. End stakes of both baselines will be referenced and a sketch made in the field book showing the staking diagram. The survey party chief will exercise good judgment in staking out these baselines in order to show the true contour of the surface of the borrow pit. Baselines for all borrow pits will be tied or referenced to a construction centerline if the centerline is within a reasonable distance. Use of this procedure will serve as a reference for final surveys and will aid the draftsman to differentiate between two or more borrow pits and the centerline areas. Borrow pits are sometimes enlarged after the original layout and field book notes have been completed. Referencing the original baseline to the centerline will aid in reestablishing the baseline should it be destroyed by enlargement of the pit.
A benchmark will be established near the site of the borrow pit preferably on the same datum governing the project. However, if an assumed datum is used, two benchmarks will be established, one at either end of the borrow pit, at locations where they will not be disturbed. Elevation and check levels will be taken on the tops of all stakes and accurate cross-sections will then be run between the corresponding stakes of the two baselines.
All breaks in contour of the ground will be shown and the measurements, both for distance and elevation will be checked between the corresponding stakes. Preliminary roadway cross- sections will be extended to cover borrow pit limits which are located adjacent to the roadway. Additional cross-sections will be taken as are deemed necessary and at a maximum A.6-14
of 50 feet (20 m) apart. Where the centerline of the roadway is a tangent, a baseline parallel to the roadway centerline will be established as described above. This will insure that the final cross-sections are taken at the same points as the preliminary cross-sections. Where the roadway centerline is not a tangent, no parallel baseline will be established.
It will be the duty of the inspector-in-charge to see that the excavation in the borrow pit is confined to the area cleared and cross-sectioned. If the limits of the borrow pit need to be extended, then the cross-sections will be extended before the additional borrow excavation is taken.
Final cross-sections will be taken after all borrow excavation is completed. All irregularities in the contour of the pit will be indicated. The final cross-sections will be run for the entire distance between the opposite stakes on each baseline and will be checked for elevation and distance. Final cross-sections will always be taken at each limit of the excavated portion of the borrow pit although a preliminary cross-section was not taken at that location. Care will be exercised in taking final cross-sections to show any waste material that may be rolled up by the shovel at the edges of the pit. All material (excepting sod and other objectionable materials removed prior to the original cross-sectioning of the pit) excavated from within the confines of the pit and wasted as unsuitable material will be measured as a solid, if the site of the waste disposal is not covered by preliminary cross- sections.
Boulders encountered in the excavation of the borrow pit and not used in the roadway embankment will be compacted and measured as a solid. This quantity will be recorded in the field book to be deducted from the borrow excavation quantities.
Before taking final cross-sections, the bottom of the pit will be leveled off and the sides smoothed up and left in a presentable condition.
A sketch of the borrow pit layout will be shown preceding the notes. The owner's name and address will also be included with this sketch. Reference's to stations on the centerline of the new construction will be indicated with the borrow pit layout. The location of reference stakes, the distance between baselines, the starting and ending of cross-sections along the baseline, and the location and description of benchmarks will be shown. All borrow pits will be serially numbered for estimating purposes.
The foregoing discussion addresses the overall requirements of borrow pit surveying procedures with emphasis on the use of conventional survey techniques. Total station procedures would also apply to the survey of borrow pits. As the procedures would vary somewhat (see Part A, Chapter 4, Section 4.5.C, page A.4-9), the results would remain the same. The use or aerial photogrammetry could also be used to produce the borrow pit surveys as outlined in Part B of this manual.
6.5 FINAL SURVEYS
Final surveys are used to determine the payable quantities items associated with various A.6-15 construction projects. A final survey is made of a project to determine the payable excavation, paving, and miscellaneous items. It is also used to show graphically the location of the road in relation to the centerline and elevations as given on the drawings. Conventional survey procedures or three-dimensional total station survey procedures, as discussed in Part A, Chapter 4 - Field Survey Procedures, will be used to perform these final surveys.
A. Requirements. All distances will be read and recorded to within 0.05 foot (10 mm), except for the reference distances to the limit of project points. Reference points will be recorded to within 0.005 foot (1 mm).
B. Procedures. All information (i.e. stations and intermediate pluses shown in the preliminary notes) from the preliminary survey will be accurately reproduced to establish the final survey line. If (due to the development for office relocation or other reason) a construction survey has been made and new cross-sections taken, then it will be necessary to reproduce the construction line in its entirety. The field books of the preliminary survey and the construction survey, together with the drawings, will be examined to determine the alignment used in the construction. The location of all stations and intermediate pluses on the preliminary survey or on the construction centerline will be accurately marked on the pavement with paint. The paint mark will be an encircled dot so the cross-section party will have no difficulty in locating these points. They also serve as a checking system during the plotting of the final survey notes. Key horizontal control points (PC's, PT's, POC's, and POT's) will be marked with a painted "X" surrounded by a circle and the station plus. Any PI's that are located on the pavement will also be located in the same manner. If preliminary control references have been destroyed during construction, then new references must be established and recorded.
Horizontal survey centerline chaining is used to relocate the preliminary or construction stationing. Final cross-sections will then be taken at the exact location of the preliminary or construction cross-sections to secure accurate earthwork quantities.
Final cross-sections will be taken at all stations and pluses and at the same angles to the centerline as the original cross-sections from the preliminary or construction survey. This will provide for the coordination of sections and the development of accurate earthwork quantities. Additional final sections will be taken at the beginning and end of all cuts and fills. The District office will interpolate the preliminary sections at these stations. The final cross- sections will be extended on each side of the centerline. The last two readings for each cross- section on each side will be original ground elevations and will be marked as "OG.” Other critical elevation readings include the bottom of fill "BF,” the top of cut "TC,” and the edge of pavement "EP.”
Ground elevations, as noted on the preliminary or construction survey, will be checked against the elevations obtained on the final survey. All discrepancies in elevations will be noted and explained. If a section falls at the inlet or outlet of a pipe, that section will be taken as if there were no break in the slope line. This will assure accurate earthwork quantities in each direction.
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Cross-sections on channel changes are usually taken shortly after completion. However, additional material may have been washed in, thereby necessitating additional cleaning to be provided. New cross-sections showing the material washed in and final cross-sections, after its removal, will then be taken for the accurate determination of quantities. When not shown on the drawings, a channel layout sketch will be prepared showing the location of the established traverse line with respect to the roadway. This sketch will be sufficiently accurate and complete such that, when plotted, the channel and roadway cross-sections can be tied in to eliminate overlapping of sections.
Final cross-sections of borrow pits will be taken as outlined in Section 6.4 - Borrow Pit Surveys.
No cross-section elevations will be required in grading sections where no "Borrow" has been used and in fill areas completed, which are beyond the theoretical cross-section limits. In waste areas, in which measurements of embankments would not be involved in the determination of the pay quantity for excavation, cross-section elevations of the fill areas will not be required beyond the outer edges of the shoulders (provided the fill slopes have been constructed properly to at least the slope as planned). The outer limits of these final cross-sections will be marked "SLW" (Shoulder Limit in Waste Areas), and embankment quantities will not need to be computed.
The benchmarks established as indicated on the construction drawings will be checked and their elevations will be recorded. Department standard benchmarks placed during construction on bridges and other permanent structures will be described in detail to be easily located in the future. The benchmark elevation will be measured and recorded to the nearest 0.01 foot (1 mm). They will be identified in the notes as new benchmarks established during construction. Any old benchmarks damaged or destroyed will also be indicated in the notes. The final drawings will void such damage or destroyed benchmarks, and will show the data for the new benchmarks established during the construction.
Measurements for the determination of final pay quantities will have been taken by the inspectors during construction or by the survey party at the time of the final survey. Usually, the inspector-in-charge of the project has recorded measurements for all items of the contract except roadway excavation, borrow, large amounts of waste material (that need cross- sectioning), parallel ditches within the cross-section area, bridge cross-sections, and approaches on which preliminary or construction cross-sections were taken.
The survey party chief will determine in advance the work needed to be done to complete the final estimates and drawings.
Final cross-sections, profiles, and measurements will be taken on all side approaches to the highway where grading has been performed (unless the quantity of cut and fill are slight and previously measured and computed by the inspectors). Layout sketches and measurements are necessary to enable the District office to accurately determine the amount of cut or fill.
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Cross drains will be measured and recorded. The station plus for the inlet, outlet, and centerline crossing, the type and size of the pipe, and the type of endwalls will be recorded. Elevations of the flow line at the inlet and outlet ends will also be recorded.
Surface measurements will be used in chaining the pavement and a recheck will be made to verify the results. The quantity of the different types of pavement surfaces will also be com- puted. Widening on curves will be measured on 10 feet (3 m) chords and aprons. Clear and accurate sketches will be shown for all additional paving beyond the normal width of the standard section and for the transition from one width to another.
Curbing, guiderail, underdrain, and similar items will be measured (in accordance with the Specifications) and located by station pluses after the pavement has been surface chained. The identification (type, size, etc.) of the contract item will be recorded.
Subsurface drain outlet endwalls, standard pipe culvert endwalls, inlets, and similar physical items, will be located by station pluses when surface chaining.
Special emphasis is placed on securing accurate quantities for all material wasted throughout the project (particularly at channels and ditches). The amount of waste material, when not obtainable by cross-sections, will be measured by average dimensions and recorded with a sketch in the field book showing its location with relation to the highway.
The survey party chief will confer with the inspector-in-charge and determine if all final computations and sketches, relating to the bridge, culvert, and channel change, have been prepared. The survey party chief will obtain any additional information when making the final survey.
6.6 PROPERTY AND RIGHT-OF-WAY ACQUISITION SURVEYS
Every right-of-way survey and drawing must be very accurate and complete, including the correct location and designation of all property ownership. Such drawings are the basis for determining all property damages that may be involved, and they are the legal records indicating the location, extent, and character of any condemnation of right-of-way.
A right-of-way survey or drawing will be premised on condemning a required width of right- of-way not less than the width of the existing right-of-way. Since the passage of Act Number 548, effective November 19, 1959, there is no fixed maximum of width for a public highway. The width to be acquired is discretionary with the Secretary of Transportation.
Since there is no longer a fixed maximum width of right-of-way, it will be general practice to extend the width of the right-of-way to include cuts and fills which previously had been acquired as slope areas. Therefore, it will be necessary in many cases to provide offsets to include such areas. These offsets will be perpendicular to the centerline and in increments of not less than 3 feet (1 m).
A survey for condemnation of right-of-way is ordinarily coincidental with the construction survey, as is outlined elsewhere in this manual. Before such survey is started, the District engineer will advise the District Survey Manager of the proposed required width of right-of- A.6-18 way, and that width will be decided only after a very careful consideration of present and future requirements.
Normal procedures for locating and establishing property lines or establishing deed boundaries do not require the retracement of deed descriptions or setting of corners (See Design Manual Part 3, Chapter 3). Obvious physical evidence such as iron pins, stone piles, blazed trees, fence rows, etc. must be included in the survey as a normal part of obtaining topography. This survey data would then be used to establish property lines as part of the right-of-way plan preparation.
If required to establish property lines due to a lack of description in the deed or due to a dispute with the owner during settlement, property lines can be established with field survey procedures. Retracement surveys or random traverse techniques would be used as appropriate. Property corners will be located directly based on retracements and through office fittings of random traverse surveys. It is very important to adequately research the property description at the county courthouse and document all decisions relating to the established property corners. Close coordination among the designer, survey party chief, District Survey Manager, and Right-of-Way Administrator is crucial to proper execution of property surveys.
A. Abandoned Canals and Railroad or Railway Right-of-Ways. Under certain conditions, the Department has the right to acquire or condemn all or part of an abandoned canal, or abandoned railroad or railway right-of-way. The application of this right is resorted to very infrequently, and when the need arises the District office will be furnished with specific and detailed instructions.
Surveys for acquiring abandoned canals, or right-of-ways of abandoned railroads or railways will be made in the same manner as any other right-of-way survey, in that, the survey corps will establish the logical centerline for the purpose of constructing a highway on the location of the abandoned canal, railroad or railway; with the exception of the fact that it is necessary to also establish the right-of-way lines on either side. In this case, the right-of-way lines are represented by the boundary lines of the abandoned canal, or railroad or railway right-of-way.
The deed applying to the abandoned canal, railroad or railway will be obtained and carefully resurveyed by the survey party and property referenced to our highway survey centerline by centerline offsets at every property corner, and between corners if considered essential.
B. Survey within the Limits of a Public Utility Commission Order. Property lines will be accurately determined and shown on the drawings. The title will be searched and uncertain property lines reestablished. All property lines will be established and referenced in relation to the survey centerline.
The property owner of record at the time the property is appropriated the post office address will be secured for each parcel, name of the grantor, date of the deed, date of A.6-19
transfer, deed book number, and number of the page on which the deed is recorded will be obtained.
Separate property surveys are no longer necessary, and will not be made unless specifically instructed to perform the property survey.
6.7 MECHANICALLY STABILIZED EARTH WALLS
Provide a survey for mechanically stabilized earth walls (MSE) 100 feet (30m) or greater in length and with an exposed height of at least 20 feet (6 m) as specified below.
A. Initial Inventory. This type of inspection provides for the collection of MSE inventory data for entry into the Bridge Management System 2 (BMS2). All items included on Form D488T1 through D488T2 must be completed for MSE walls with a length in excess of 100 feet (30m) and height of at least 20 feet (6 m).
Should it be determined that permanent monumentation is required, it is to be established according to the Department’s Publication 122M, Part 2, Chapter 3, Section 3.5. All permanent monuments will be referenced and recorded on Form D-428 in accordance with Publication 122M. Permanent monumentation is to be established outside of areas potentially affected by future wall movement.
A detailed 3-dimensional as built survey must be provided upon completion of construction all MSE walls with a minimum of length of 100 feet (30m) and minimum height of 20 feet (6m). A minimum of one (1) 3-dimensional coordinate shall be furnished every 10 feet (3m) horizontally and 10 feet (3m) vertically along the entire length of wall. This survey shall be referenced to the permanent monumentation as described above. The horizontal and vertical accuracy will be 0.036 feet (10mm).
Deliverables: See Part 1, Chapter 9, Section 9.9.
B. Routine Inventory. This type of inspection provides for the 3-dimensional data collection of MSE walls every five (5) years from the date of the initial inventory.
A minimum of one (1) 3-dimensional coordinate shall be furnished every 10 feet (3m) horizontally and 10 feet (3m) vertically along the entire length of wall. This survey shall be referenced to the permanent monumentation as described above. The horizontal and vertical accuracy will be 0.036 feet (10mm).
Deliverables: See Part 1, Chapter 9, Section 9.9.
C. Movement Detected between Initial and Routine or Special Inventory. Following each routine, or other specified interval of inspection, initial and routine (or special) 3-dimensional scanned inspection files will be compared using Micro Station InRoads or other equivalent software to identify movement of MSE walls. Surveyed movements of MSE walls with differences larger than 0.05 foot (.003m) will be reported to the Photogrammetry & Surveys A.6-20
Section within three weeks of inspection using 1”=10’ (1:100) profile plots. Differences will be color coded as described below:
Fig. 6.7.1 Color Coding of MSE Wall Movement
Distance Color 0.00’ to 0.05’ (0.0 to 0.015m) Green 0.051’ to 0.07’ (0.0155 to 0.02m) Yellow >0.071 (>0.021m) Red
Deliverables: See Part 1, Chapter 9, Section 9.9. Hard copy and digital files of 1”=10’ (1:100) profiles. A.7-1
CHAPTER 7
FIELD BOOK COMPILATION, FORMAT, AND RECORDINGS
7.0 INTRODUCTION
Survey notes are original records and care will be exercised to guard against the loss of and/or the damage to any field books. Each survey party chief or other person using a field book will be charged with its safe custody and will be responsible for returning it in good condition to the District or to their immediate superior. Valuable field books have been lost in the past and, to avoid this, dated receipts will be given for the passing of field books from one person to another. Pages will not be removed from a field book for any reason. All notes that are obsolete will be marked accordingly. All recorded notes will be clean and legible.
7.1 ACCEPTANCE REQUIREMENTS FOR CONSULTANT SURVEYS
A. Preparation of Field Books. The drawings and the efficiency with which they are prepared depend largely upon the adequacy and clarity of the survey notes. Incomplete and illegible notes are usually due to carelessness. The person plotting the survey notes will rarely have the advantage of being in direct contact with the original note taker. Therefore, the survey notes should be clear and complete, to present a mental picture of the field location or field condition to the draftsman. If you feel further, details will present the picture in a clearer manner, show a sketch in the back of the book with a reference to it in your notes. A sketch in the back of the book with reference to the field notes may also be used to clarify any confusion.
All survey notes will follow the standards as described and use the symbols as shown in this manual. All notes will be lettered using the appropriate abbreviations, if necessary, as given in Section 7.2 - Abbreviations. Computations for curves, levels, etc., will be made and kept on the last few pages of the field book to which they apply. Do not perform these basic computations on scratch paper to be thrown away. Notes will be kept with a sharp, hard pencil.
Before turning field books into the District, all computations will have been completed and checked by competent members of the survey party. Upon completion of a survey, all field books will be assembled in order and forwarded to the District. If the District requires the field books as the survey progresses, sufficient information will be copied into the next field book in order to proceed with the work. All copied notes will be indicated as so to differentiate between the original notes and the copied notes.
Standard methods of keeping notes are shown as part of Appendix B - Sample Field Book Entries.
A.7-2
7.2 ABBREVIATIONS
The specific terminology and associated abbreviations indicated herein are provided for uniformity and for general use by personnel engaged in engineering field surveys.
A. General Abbreviations - A - ABANDONED…………….ABD APPROXIMATE……………… APPROX ABUTMENT……………….ABUT ASPHALT COATED ACRE...... a CORRUGATED METAL AGGREGATE ...... AGGR PIPE…………………………. ACCMP AHEAD ...... AHD AVENUE……………………… AVE ANGLE ...... ANGLE AVERAGE……………………. AVG APPLICATION ...... APPL APPROACH……………… .. APPR - B - BACK……………………… BK BOTTOM……………………... BOT BACKSIGHT………………. BS BOTTOM OF BANK…………. BB BARN……………………… BARN BOTTOM OF CURB…………. BC BASELINE………………… BL BOTTOM OF CUT…………… BC BASEMENT……………….. BSMT BOTTOM OF FILL…………… BF BEAM………………………BEAM BOTTOM OF STAKE…………BS BEARING…………………. BRG BOTTOM OF WALL………….BW BENCH MARK…………….BM BOULDERS…………………... B BITUMINOUS SURFACE BOULEVARD………………...BLVD COURSE………..BIT SURF CRSE BRICK………………………… BRICK BOROUGH………………… BORO BUILDING……………………. BLDG - C - CAST IRON PIPE……… CIP CONTINUED………………..... CONT'D CATCH BASIN...... CB CONTROL POINT………….... CP CEMENT ...... CEM CORNER…………………….... COR CEMETERY ...... CEMETERY CORRUGATED METAL CENTER TO CENTER ...... C TO C PIPE…………………………. CMP CENTERLINE ...... CL COUNTY……………………... CO CHURCH ...... CH CREEK………………………... CK COATED ...... CT'D CROSS SECTION……………. X-SECT CONCRETE ...... CONC CUBIC FOOT………………… cu ft or ft3 CONCRETE PIPE ...... CP CUBIC METER………………. m3 CONDUIT ...... CONDUIT CUBIC YARD………………..cu yd or yd3 CONSTRUCTION ...... CONSTR CULVERT……………………. CULV - D - DEFLECTION ...... DEFL DIRECTIONAL……………….DIR DEGREE (ANGLE DOWNSTREAM………………DWNSTR MEASURE) ...... DEG or DRIVE…………………………DR DIAMETER ...... DIA or φ DWELLING…………………...DWLG DIMENSION ...... DIM A.7-3 - E - EDGE OF CONCRETE ...... EC ENDWALL…………………… EDW EDGE OF PAVEMENT ...... EP EQUAL……………………….. = EDGE OF ROAD ...... ER EQUATION…………………... EQN EDGE OF SHOULDER……...ES EXCAVATION………………. EXC EDGE OF STREAM ...... E STRE EXISTING……………………. EXIST ELEVATION ...... ELEV EXPANSION…………………. EXP EMBANKMENT ...... EMB - F - FACE OF CURB ...... FC FORESIGHT………………….. FS FENCE POST ...... FP FOOT, FEET………………….. ft or ’ FIRE HYDRANT ...... FH FOUNDATION……………….. FDN FLOOR ...... FLR FRAME DWELLING………… FR DWLG FLOW LINE ...... FL - G - GARAGE ...... GAR GUIDE RAIL POSTS………… GP GUIDE RAIL ...... GR - H - HECTARE ...... ha HORIZONTAL……………….. HOR HEIGHT OF INSTRUMENT.. HI HOUSE………………………... HSE HIGHWAY ...... HWY - I - INCH...... in or ” INVERT………………………. INV INFORMATION ...... INF IRON PIN……………………... I PIN INSIDE DIAMETER ...... ID IRON PIPE……………………. IP - J - JOINT ...... JT JUNCTION BOX……………... JB - K - KILOMETER ...... km - L - LAKE ...... LAKE LONGITUDINAL…………….LONG LEFT ...... LT - M - MAGNETIC ...... MAG MILLIMETER………………... mm MANHOLE ...... MH MINIMUM……………………. MIN MASONRY ...... MAS MINUTE (ANGLE MAXIMUM ...... MAX MEASURE)……………………MIN or ’ METER ...... m MONUMENT………………….MON MILE...... Mi MOUNTABLE………………...MTBLE - N - NUMBER ...... NO - O - OFFSET ...... OFF OUTSIDE DIAMETER………. OD ORIGINAL GROUND ...... OG A.7-4 - P - PAVEMENT ...... PAV'T PLAIN………………………PL PERCENT ...... % PROFILE GRADE…………PG PERFORATED ...... PERF PROPERTY LINE…………. PL PERMANENT ...... PERM - R - RAILROAD ...... RR REQUIRED………………... REQ'D RAILWAY ...... RWY REVISION………………… REV REFERENCE ...... REF RIGHT……………………... RT REINFORCED ...... REINF RIGHT-OF-WAY…………..R/W REINFORCED CEMENT ROAD………………………RD CONCRETE ...... RCC ROADWAY……………….. RDWY REINFORCED CONCRETE ROUTE…………………….. RTE PIPE ...... RCP - S - SANITARY SEWER ...... SAN S STATE ROUTE………………. SR SECOND (ANGLE STATION……………………... STA MEASURE) ...... SEC or ” STEEL………………………… STL SECTION ...... SECT STORY………………………... STY SEGMENT ...... SEG STREAM……………………… STRE SHOULDER ...... SHLDR STREET………………………. ST SIDEWALK ...... S'WALK SUBGRADE………………….. SUBG SIGNAL ...... SIG SUBSTRUCTURE……………. SUBSTR SQUARE...... SQ SUPERELEVATION…………. SE SQUARE FOOT...... sq ft SUPERSTRUCTURE………… SUPERSTR SQUARE METER ...... m2 SURFACE…………………….. SURF SQUARE MILE...... sq mi SURVEY……………………… SURV STANDARD ...... STD - T - TELEPHONE ...... TEL TOP OF RAIL………………… TR TELEPHONE POLE ...... TP TOP OF STAKE……………… TS TEMPERATURE ...... TEMP TOP OF WALL………………. TW TERRA COTTA PIPE ...... TC TOPOGRAPHY………………. TOPO TOP OF BANK ...... TB TOWNSHIP…………………... TWP TOP OF CURB ...... TC TRANSVERSE……………….. TRANSV TOP OF CUT ...... TC TURNING POINT……………. TP TOP OF FILL ...... TF TYPICAL……………………... TYP TOP OF GRATE...... TG - U - UNDERDRAIN ...... U-DRAIN UPSTREAM…………………... UPSTRE - V - VARIABLE ...... VAR VITRIFIED CLAY PIPE……. VCP VERTICAL ...... VERT
A.7-5 - W - WALK ...... WK WIDENED CURVE………….... WC WEARING SURFACE ...... WEAR WINGWALL………………….. WW …………………… ...... SURF WORK POINT……………….... WP
B. Horizontal Curve Data Abbreviations DELTA - EXTERNAL POINT OF INTERSECTION….. PI ANGLE ...... Δ POINT OF REVERSE EXTERNAL DISTANCE ...... E CURVE………………………. PRC LENGTH OF CURVE ...... L POINT ON SUBTANGENT…... POST POINT OF COMPOUND POINT OF TANGENT………… PT CURVE ...... PCC POINT ON TANGENT….…….. POT POINT OF CURVE ...... PC RADIUS………………………..RAD or R POINT ON CURVE ...... POC TANGENT……………………... T
C. Transition (Spiral) Curve Data Abbreviations CENTRAL ANGLE SIMPLE CURVE BETWEEN THE SC CO-ORDINATE (Ordinate)….. p AND CS ...... ΔC SPIRAL ANGLE……………….θS CURVE TO SPIRAL POINT….CS SPIRAL LENGTH……………... LS DEFLECTION ANGLE………. Δ SPIRAL TO CURVE POINT….. SC EXTERNAL DISTANCE …….. ES SPIRAL TO TANGENT LENGTH OF CIRCULAR POINT………………………….. ST CURVE ...... LC TANGENT DISTANCE……….. TS LONG CHORD ...... LC TANGENT DISTANCE LONG TANGENT ...... LT FOR SC…………………………xC RADIUS OF CIRCULAR TANGENT OFFSET OF CURVE ...... RC THE SC………………………… yC SHORT TANGENT ...... ST TANGENT TO SPIRAL SIMPLE CURVE POINT………………………...... TS CO-ORDINATE (Abscissa)… .. k
D. Vertical Curve Data Abbreviations HEAD LIGHT SIGHT POINT OF VERTICAL DISTANCE ...... HLSD CURVE………………………. PVC LENGTH OF VERTICAL POINT OF VERTICAL CURVE ...... VC TANGENT…………………… PVT MIDDLE ORDINATE ...... MO STOPPING SIGHT POINT OF VERTICAL DISTANCE…………………... SSD INTERSECTION ...... PVI
E. Directional Abbreviations EAST ...... E SOUTH………………………. S EASTBOUND ...... EB SOUTHBOUND……………...SB NORTH ...... N WEST………………………… W NORTHBOUND ...... NB WESTBOUND………………. WB A.7-6 7.3 FIELD BOOK ENTRIES Generally, three types of notes appear in a survey field book. These notes may be in the form of a sketch, a description, or a table. In addition, these types are often combined to further assist in conveying the survey information from the field to the office.
The type of notes prepared in the field book is dependent on the specific survey procedure being performed. These types, and their corresponding field book entry requirements, are discussed in this section with illustrations provided as part of Appendix B - Sample Field Book Entries.
A. Front Page. The front page of field books (Form 428) on all surveys will show the dates of starting and of completing of the survey, the route number, the section number, the application number, the township, the borough, the city, the county, the District Engineer's name, the address of the District office, the Department District number and the names and the titles of the survey party. The pages of the field books are numbered and a complete table of contents will be shown under “Index.” The type of survey and notes in each field book will also be designated. Each page of the field book will show the date, the names of the survey party, and the weather conditions. A typical front page is illustrated in Appendix B, Figure B.1.
B. Alignment. All alignment information is recorded in the field book in accordance with Appendix B - Sample Field Book Entries. Control traverse sketches will be provided on the left-hand page of the field book with the corresponding control point information recorded on the right-hand page. All distances between control points will be recorded to two decimal places of a foot (three (3) decimal places of a meter). All angular measurements will be recorded to the nearest 1 second. Control point information will include the northing value, the easting value, and the elevation. A control traverse sketch is included in Appendix B, Figure B.2.
A detailed control point sketch is provided in Appendix B, Figure B.3. All distances (including swing ties to centerline / baseline) will be recorded to two (2) decimal places of a foot (three (3) decimal places of a meter).
Appendix B, Figure B.4 shows a centerline alignment for a curve on the left-hand page with the corresponding reference ties on the right-hand page. All control point information (including reference tie information) will be recorded to two (2) decimal places of a foot (three (3) decimal places of a meter). Deflection angles will be recorded either at 50’ (20 m) intervals (for curves over 300’ (100 m) radius) or at 30’ (10 m) intervals (for curves equal to or less than 300’ (100 m) radius) to the nearest 1 second.
C. Topography. Documentation requirements for observed topographic features are dependent on the specific survey procedure used. These survey procedures (Chapter 4 - Field Survey Procedures, Section 4.4 - Topography) include both the conventional method and the total station method. The following is the specific set of requirements for recording topographic information for each survey procedure:
A.7-7 Conventional Method. All topographic features (as discussed in Chapter 4 -Field Survey Procedures, Section 4.4 - Topography) are recorded by noting the "plus" distance along the centerline from the last full station and the right angle "offset" distance located from the centerline to the object. In addition, topographic features will be recorded at radial offset distances along curves. All distances will be recorded to one (1) decimal place of a foot (two (2) decimal places of a meter). The whole kilometer stations will be labeled and circled on a vertical line, which represents the roadway centerline. Additional stations will be recorded at 50’ (20 m) intervals. All stationing will be labeled in ascending order from the bottom of the page to the top of the page. A straight line in the field book will be used to represent a horizontal curve. The proper field book format for a typical, conventional method, survey for topography is shown in Appendix B, Figure B.5.
Total Station. All topographic features (as discussed in Chapter 4 - Field Survey Procedures, Section 4.4 - Topography) are recorded by noting the "plus" distance along the centerline from the last full station. These distances will be recorded to one (1) decimal place of a foot (two (2) decimal places of a meter). The whole kilometer stations will be labeled and circled on a vertical line, which represents the roadway centerline. Additional stations will be recorded at 50’ (20 m) intervals. All stationing will be labeled in ascending order from the bottom of the page to the top of the page. A straight line in the field book will be used to represent a horizontal curve. The proper field book format for a typical, total station method, survey for topography is shown in Appendix B, Figure B.6.
Additional field book entries will be required to supplement the topography sketches. These field book entries would include instrument location, backsight location, and foresight location. The foresight location will include horizontal angle, distance (if not horizontal, a vertical angle will be recorded), and description. Appendix B, Figure B.7 shows a typical reference point sketch and can be cross referenced with the information provided in Appendix B, Figure B.6.
Appendix B, Figure B.8 illustrates a typical field book entry for indexing all topographic features that are recorded in an electronic data collector.
D. Cross Sections. Field book entry requirements for cross section information are dependent on the specific survey procedure used. These survey procedures (Chapter 4 - Field Survey Procedures, Section 4.5 - Cross Sections / Profiles) include both the conventional method and the total station method. The following is the specific set of requirements for recording cross section data for each survey procedure:
Conventional Method. Rod readings for existing pavement elevations are recorded to the nearest .01’ (1 mm) and for natural ground elevations are recorded to the nearest 0.05’ (10 mm). Distances to culvert endwalls, pavement edges, and ground shots should be carefully measured and recorded to the nearest .05’ (10 mm).
Cross section data are recorded in the notes opposite the station number in fractional A.7-8 form with the rod reading as the numerator and the distance from centerline as the denominator. Care must be taken to record readings correctly as to the left or right of the centerline. Appendix B, Figure B.9 is a typical cross section field book entry for a conventional survey method. Total Station. Cross section data will be taken during the topography surveys. However, all cross section information obtained electronically will be converted to the format shown in Appendix B, Figure B.10 and will be mounted in a standard field book for submitting to the District.
E. Profiles. All profile information is recorded in the field book in a format based on the survey procedure. As with cross section data, profile information is gathered either by conventional method or by total station method.
Conventional Method. Benchmarks will be established in the standard manner to the nearest 0.01 foot (1 mm). Profile readings for existing pavement elevations are recorded to the nearest 0.01 foot (1 mm) and for original ground elevations are recorded to the nearest 0.05 foot (10 mm).
Profile data are recorded in the notes opposite the station number with the rod reading recorded then the elevation computed to the requirements previously outlined. Appendix B, Figure B.11 is a typical profile field book entry established by conventional survey methods.
Total Station. Profile information will be taken during the topography surveys. However, all profile information obtained electronically will be converted to the format shown in Appendix B, Figure B.12 and will be mounted in a standard field book for submitting to the District.
F. Bench Levels. Bench level circuit data will be recorded as shown in Appendix B, Figure B.13. As indicated, all rod readings will be measured and recorded to the nearest 1 mm. Information such as the "+" values, the "-" values, and the "HI" values, along with the computed "ELEV's" will be recorded on the left-hand page of the field book. All bench mark data will be provided on the right-hand page and will be formatted as shown in Appendix B, Figure B.13 and in accordance with Chapter 3, Section 2.6 of Design Manual, Part 3.
G. Survey Supervisor Check-off List for Form D-428 (survey field book) Project: Date: 1. Inside front cover must be completely filled in. 2. On inside front cover, complete check off list. 3. Dates must be enter on all pages containing entries. 4. Weather conditions and air temperature must be entered on all pages containing entries. A.7-9 5. Field book entries must be formatted in accordance with Pub 122M, Part 1 Chapter 7. 6. Note horizontal datum. 7. Traverse, angles, and distances measured to accuracy standards according to Pub 122M, Part 1 Chapter 1. 8. Enter traverse sketch(s) into field book. 9. Enter a note if traverse is adjusted, not adjusted, adjustment method, and unadjusted and adjusted coordinates. 10. Enter 3D survey notes into a separate field book. 11. Enter bridge structure sketch(s). 12. Enter benchmark description tied to Segment and Offset. 13. Enter vertical datum. 14. Enter a list of point numbers for all property corners located on project. 15. All entries must be checked by and initialed on notes and calculations on each page containing entries. 16. When applicable, complete a survey report.
H. Field Book Numbering. Contact the District Survey Manager to obtain the proper number.
A.8-1 CHAPTER 8
GLOBAL POSITIONING SURVEYS
8.0 INTRODUCTION
An understanding of measurements and computations is an essential aspect of the surveying profession utilizing Global Positional Systems (GPS) equipment. This Chapter outlines various applications, procedures, and specifications for the use of survey and mapping types of GPS equipment.
8.1 EQUIPMENT SPECIFICATIONS, CALIBRATION, AND CARE
Basic instrumentation for a GPS network survey includes multiple sets of receivers, antennas, fixed-height tripods, etc. Identical equipment should be used whenever possible to minimize the effect of equipment biases. The compatibility of mixing different instrument models or brands should be demonstrated by performing a validation survey.
Survey equipment, like all scientific instrumentation, should be handled with care, maintained according to manufacturing specifications, and calibrated on a regular basis. An equipment calibration should be performed at the start and end of a project, before and after any maintenance, and at sufficient intervals to maintain data integrity. Any data not bracketed by successful calibrations are suspect. To prevent the invalidation of good data, frequent calibrations are recommended. The entire system of GPS equipment, personnel, and processing procedures should be proven with a validation survey as a final check to ensure all components interact properly. The following equipment is described below:
A. Receiver Specifications B. Antenna Specifications C. Tripod Specifications D. Tribrach Specifications E. Personnel specifications
A. Receiver Specifications: The receivers used for network surveys should record the full wavelength carrier phase and signal strength of both the L1 and L2 frequencies, and track at least eight satellites simultaneously on parallel channels. Dual frequency instruments are required for all baselines longer than 6 mile (10 km). Receivers should have completed instrument testing by the Federal Geodetic Control Subcommittee (FGCS). Receivers should have sufficient memory and battery power to record 6-hours of data at 15 second epochs. Receiver at Hub Stations should have sufficient memory and power to record 72 continuous hours of 30-second epochs. A.8-2 Receiver Calibration and Care: Ensure that your receiver contains the latest manufacturer’s firmware upgrades. A zero- baseline test can measure receiver internal noise if the performance is suspect. Consult your user’s manual for additional specifications.
B. Antenna Specifications: The antennas should have stable phase centers and choke rings or large (greater then 16 cm) ground planes to minimize multipath interference, and a common orientation indicator (e.g. an arrow) to point north during observations.
Antenna Calibration and Care: All antenna models used shall have completed Antenna Calibration by the National Geodetic Survey (NGS). Consult your user’s manual for other specifications.
C. Tripod Specifications: The tripods used must facilitate precise offset measurements between the mark datum point and the Antenna Reference Point (ARP). Fixed height tripods are preferable, due to the decreased potential for antenna centering and height measurement errors.
Tripod Calibration and Care: All tripods shall be examined for stability with each use. Ensure that hinges, clamps, and feet are secure and in good condition.
Fixed-height tripods shall be tested for stability, plumb alignment, and height verification at the start and end of each project.
D. Tribrach Specifications: Tribrachs used shall be of suitable quality and condition for high-accuracy surveys. Consult with the Departments District Survey Manager for details.
Tribrach Calibration and Care: The optical plummet alignment shall be tested at the start and end of each project.
E. Personnel Specifications: All field personnel should be trained in the avoidance of systematic errors and blunders during field operations. Field personnel often work alone and must be prepared to make wise, on the spot decisions regarding mark identification and stability, equipment use and troubleshooting, and antenna setup. Office personnel should be familiar with geodetic concepts and least-squares adjustments. Personnel should participate in any certification and training activities.
A.8-3 8.2 Control Surveys - General
GPS control established for 3D and 2D surveys consists of two separate tasks: Primary Control Networks and Real Time Kinematic Control Surveys. All control surveys will be based on National Geodetic Reference System (NGRS) stations.
A. Standards and Specifications. Federal Geodetic Control Subcommittee (FGCS), formerly the Federal Geodetic Control Committee (FGCS) publishes standards and specifications for geodetic control surveys in the United States. The document pertaining to conventional geodetic control surveying (traverse, triangulation, and differential leveling) is "Standards and Specifications for Geodetic Control Networks." Corresponding documents for Global Positioning System surveys is "Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques,” and “Geospatial Positioning Accuracy Standards, Part 2: Standards for Geodetic Networks” are to be used by the Department and its consultants when finalized and deemed necessary.
B. Classification of Accuracy. A horizontal control survey is classified as meeting a given accuracy standard when the propagated relative error at the 95 percent (two-sigma) confidence level, for all station pairs, is less than the maximum allowable error, s, for the Order of accuracy specified for the project. Maximum allowable error, s, is computed as:
US Survey Feet s = 0.033 (32.81e )2 +( 0.16 pd )2 Metric s = 0.01 ( 0.1e )2 +( 0.1pd )2 where s = maximum allowable one-dimensional error in feet (meters) at the 95 percent (two-sigma) confidence level. d = distance in miles (kilometers) between any two stations. p = the line length dependent geometric relative positioning accuracy standard in parts per million (ppm.) e = base error in hundredths of a foot (millimeters) (this includes station dependent setup errors.) Table 8.2.1 lists the values of p and e for the different Order classifications applicable for Department work. Table 8.2.1 e and p Values
GROUP ORDER CLASS e foot (mm) p (ppm)
C 1 0.03 (10) 10 C 2 I 0.06 (20) 20 C 2 II 0.10 (30) 50 C 3 0.16 (50) 100
A.8-4 For a GPS network, the propagated relative error will be computed using a least squares adjustment for all three dimensions (X, Y, and Z or N, E, and U) with a 95 percent (two- sigma) confidence criteria. Accuracy classification of a GPS relative positioning survey may be determined in one of two ways, dependent upon the project classification. A "geometric" classification may be made where the confidence tests are imposed upon a minimally constrained (free) least squares adjustment independent of the local geodetic reference system external control. Geometric classifications are applicable to project specific control systems such as those developed for specialized design surveys and monitoring networks. The second method for classifying GPS relative positioning surveys is an "NGRS" classification determined from a least squares adjustment constrained to the local geodetic reference system, holding the external control fixed. This method is a good measure of the accuracy of a network when the local geodetic reference system is of higher accuracy than the new observations (i.e. when a statewide HARN is used.) Advances in GPS technology have provided new systems to be used in addition to traditional NGRS concrete monuments. NGRS permanently mounted GPS antennae, such as continuously operating reference stations (CORS) and virtual reference systems (VRS – a network of CORS with real-time kinematic capability), are now augmenting for and with traditional monumentation.
While a least squares adjustment is preferred, simple traverse lines may be adjusted using the compass rule or other error distribution methods.
Accuracy classification for differential leveling is expressed as follows:
US Survey Feet e = 1.609M Metric e = k where e is the allowable error in feet (meters) for a level run of M (miles) or k (kilometers) in length, and μ is a factor which depends on the Order of accuracy desired. Differential leveling runs for Department projects are to be done to a minimum accuracy of Second Order, Class II leveling, where μ is 0.026 foot or (0.008 meters)
C. Datums. By state law, effective January 1, 1996, all Pennsylvania State Plane Coordinate Survey information will be computed in the North American Datum of 1983 (NAD83). By policy decision, effective January 1, 1996, all vertical survey information will be computed in the North American Vertical Datum of 1988 (NAVD 88).
Prior to January 1, 1996, the North American Datum of 1927 (NAD 27) and the National Geodetic Vertical Datum of 1929 (NGVD 29) had been used for project datum’s. NAD 27 and NGVD 29 may no longer be used for Department projects.
Acceptable surveys will be balanced in accordance with Chapter 4 of "State Plane Coordinate System of 1983" by the National Geodetic Survey. From which NGS has compiled new standards and constants for each State as part of the newer horizontal control network which is referred to as the State Plane Coordinate System of 1983 (SPCS 83). A.8-5
Subsequent surveys using these control stations may require adjustment from grid azimuths and distances. Ground level distances must be derived by dividing the grid distance by the grid factor (product of scale factor and elevation factor). Ground level angles (and bearings) may be very close and acceptable for field use without further consideration. The decision to adjust grid azimuths for field use must be based on the significance of the adjustments with respect to the precision of the instrument.
On February 10, 2007, the National Geodetic Survey completed a national readjustment of all National Geodetic Reference System (NGRS) stations that had their positions determined exclusively by GPS observations. This new national readjustment provides a homogeneous network of all NGRS GPS observed stations (C.O.R.S., H.A.R.N., F.B.N., C.B.N., P.A.C.S., S.A.C.S., etc…) across the nation. The new datum adjustment tag is NAD83 (NSRS2007), better known as NAD83 (2007). As noted above, all Department control surveys will be based on NGRS stations. Thereby, all Department control surveys will be tied to and noted with the NAD83 (2007) datum adjustment tag.
8.3 GLOBAL POSITIONING SYSTEM
Global Positioning System (GPS) is a Department of Defense navigation system which uses an orbiting system of satellites carrying precise atomic clocks to determine position in real time, anywhere on earth, to an accuracy of 30 feet (10 m). By using two or more receivers collecting data from the same satellites simultaneously, and processing the data, it is possible to determine relative positions to sub-centimeter accuracy. There are two basic methods in GPS surveying: carrier phase and code.
A. Carrier Phase Tracking. The most accurate GPS method is carrier phase tracking, which results in typical accuracies of 0.02 foot to 0.06 foot (0.005 m to 0.02 m) 1 to 3 parts per million (ppm) of the distance between stations. Carrier phase technique involves resolution of the phase of the carrier to about 0.006 foot (0.002 m). However, it is necessary to determine the integer number of wavelengths (integer bias) passed before signal acquisition and tracking began. A minimum of four (4) satellites are required to be tracked at fixed epoch intervals. Carrier phase can be further broken down into static and kinematic surveying. Static surveying is the most accurate, and involves the simultaneous occupation of the survey stations for a period of 45 minutes or more. Dual frequency techniques (using L1 and L2, rather than just L1) can shorten the required time to several (1 to 20) minutes over short to medium <6 miles (< 10 km) length lines. This is known as fast or rapid static. Shorter observation times can be affected by multipath. Multipath is the error introduced by the radio wave being reflected by a nearby surface and introducing added length into the distance from the satellite. Because of multipath, it is important to select open sites when using fast ambiguity resolution techniques. Negative effects of multipath tend to cancel out as the length of the observing session increases. Kinematic surveying yields centimeter accuracy once the integer biases are resolved. As long as lock is maintained on the satellite signals (4 or more), the receiver can be moved and, once stationary, can resolve the baseline in seconds rather than minutes or hours necessary in static A.8-6 surveying. Real time kinematic surveying is possible using a radio link between the receiver at a known point (base) and a roving receiver. Data from the base and rover is combined and processed on board the roving receiver to yield centimeter accuracy.
B. Code Tracking. The other GPS method being used is known as code. This uses broadcast data from the satellite to determine autonomous positions. Theoretical autonomous accuracy is about 30’ (10 m). By using two receivers, one on a known survey station, it is possible to correct the observations to attain an accuracy of better than 3 feet (1 m).
C. GPS Techniques. When the Global Positioning System (GPS) is used, the specifications outlined in "Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques,” by the FGCS, for Group C, First Order surveys should be adhered.
D. Redundancy. Redundancy can provide proof of the precision to which a measurement is made. In order for this proof to be valid, the inclusion of possible error sources must not be systematically duplicated in the repeat measurements. Redundancy in a GPS survey is achieved primarily by way of a change in the relative geometry of the satellite constellation. For GPS surveys, the geometry of the satellite constellation must be different for repeat station occupations in order to eliminate potential sources for systematic errors due to multipath, orbital bias, and unmodeled ionospheric and tropospheric delay. Even if the repeat observation is made on another day, data must be collected at a different sidereal time in order to obtain a different satellite configuration. Redundant observations also provide the additional verification of centering errors and a second set of antenna height measurements.
E. Specifications. When a station is to be occupied more than once in consecutive sessions, the tripod should be reset between occupations. At least 20% of the stations should be occupied three or more times. At least 5% of the total number of independent baselines should be measured twice. The precise ephemeris is required for the Primary Control Network. If a fixed height tripod is used, the nominal height and the manufacturers name and model number should be recorded. If a variable height tripod is used, the height must be measured in meters with separate measuring scales at both the start and the end of each observing session and recorded. Tribrachs and other centering devices should be checked on a weekly basis, and a log kept of the results. A log sheet must be prepared for each occupation, and must include as a minimum the following data: name of operator, antenna and instrument serial and model numbers, centering device identifier, height of instrument, C/A code position, unhealthy satellites, start and stop times, station name, description, sketch (sketch not necessary for consecutive occupations), and a description of any problems or unusual occurrences during the observation.
F. Network Design. The network should be designed to enable loop closure analyses to be performed on all stations. A loop is defined as a series of independent baselines (measured at different times) which form a geometrically closed polygon. The maximum permissible misclosure in terms of loop length is 12.5 ppm. A.8-7
G. Least Squares Adjustments. A minimally constrained and a fully constrained adjustment of the GPS network will be analyzed and supplied. Geoid heights from the latest geoid model available from the National Geodetic Survey must be included. The adjustment must only use independent (non-trivial) vectors. The following statistics must be evaluated for each adjustment:
Network variance of unit weight (variance factor) and degrees of freedom. A variance factor of less than 1.5 and approaching 1.0 is considered a conservative statistic for geodetic control surveying. Posteriori errors must be computed at the 95% (two-sigma) confidence level for the adjusted station coordinates and for relative positions for all station combinations.
Any significant changes between statistics from minimally constrained adjustment and fully constrained adjustment must be investigated.
8.4 PRIMARY CONTROL NETWORKS
Primary Control Network (PCN) consists of permanent stations marked by Pennsylvania Department of Transportation disks set in concrete, grouted in outcropping bedrock or other massive or permanent structures, or similar existing monuments of other agencies. Exceptions to the monumentation standard must be approved by the “District Survey Manager.” The minimum requirements for concrete monuments are a 3 feet (1 m) long by 8 inch (0.20 m) in diameter. A steel reinforcing rod 24 inch long (600mm) must be placed in the monument. The bottom will be belled out to a diameter twice that of the monument 1.5 foot (0.50m). A properly stamped PennDOT bronze disk will be placed on top of the concrete with the two tongues on the back of the disk slightly widened. PA ONE CALL is to be contacted to assure underground utilities will not be damaged. The required spacing of the permanent control is 2 miles (3 km) intervals. Each monument set will have a minimum of two (2) azimuth marks, set at a minimum distance of 1320 feet (400 m) from the permanent control monument. Acceptable azimuth marks include concrete monuments, radio towers and antennas, and adjacent primary stations, which are inter-visible. A completed Department “Record of Control Sheet- Horizontal” (see Appendix C-3) in digital format, as approved by the District Survey Manager, must be prepared for each station.
The minimum acceptable accuracy for the Primary Control Network is Group C, First Order, 10 ppm when using the Global Positioning System. External horizontal control (NGRS) must be brought in to the stations of the Primary Control Network.
If GPS elevations are required (acceptable for mapping at contour intervals of 2.0 feet (0.5 m) and above), a minimum of four Second Order or higher NGRS , or Third Order PennDOT vertical control stations will be occupied, distributed in at least three quadrants around the center of the project. If a sufficient number of NGRS benchmarks are not available, and with the approval of the “District Survey Manager,” Third Order marks of other agencies may be used. If A.8-8 other marks are used, a Third Order level line should be run through the long dimension of the project, passing through as many monuments as possible.
The vertical component of the PCN will be determined by differential leveling techniques. Benchmarks are required at 0.50 miles (0.75 km) intervals. A completed Department “Record of Control Sheet – Vertical” (see Appendix C-4) in digital format and also manually recorded in Form D-428, as approved by the Department’s District Survey Manager , must be prepared for each benchmark.
Differential Leveling: A geodetic level and wooden or invar rod(s) or fiberglass bar coded rods are required for differential leveling. Procedures are outlined in "Standards and Specifications for Geodetic Control Networks", by FGCS, for Third Order leveling shall be adhered to, with the exception that the level rod may be of wood, metal, or bar coded fiberglass construction, and must be not more than 12 feet (4 m) in length.
All survey work related to vertical control networks will be categorized as shown in Table 8.3.1. Table 8.3.1 is a compilation of information outlined in "Standards and Specifications for Geodetic Control Networks" by the Federal Geodetic Control Committee.
Table 8.3.1 Vertical Control Accuracy Requirements
ORDER Third
LEVELING Maximum Sight Length feet (m)...... 300 (90) Difference of Foresight and Backsight never to Exceed.…. 100 (10) Minimum Ground Clearance of Line of Sight feet (m)....… 1.5 (0.5)
LOOP MISCLOSURE Loop Misclosure not to Exceed (feet)………………….. 0.026 1.609M (meters)……………….. (0.008 K )
8.5 PROJECT SPECIFIC CONTROL NETWORKS
Project Specific Control Network (PSCN) consists of 24 inch (600mm) steel rebars in open ground, Mag Nails™ in bituminous pavements, drill holes in concrete or other methods. Exceptions to other methods of monumentation standard must be approved by the “District Survey Manager.” The required spacing of the permanent control is 2 miles (3 km) intervals. Each monument set will have a minimum of two (2) azimuth marks, set at a minimum distance of 1320 feet (400 m) from the permanent control monument. Acceptable azimuth marks include concrete monuments, radio towers and antennas, and adjacent primary stations, A.8-9
which are inter-visible. A completed Department “Record of Control Sheet” in digital format, as approved by the Departments District Survey Manager, must be prepared for each station.
The minimum acceptable accuracy for the Project Specific Control Network (PSCN) is Group C, First Order, 10 ppm when using the Global Positioning System. External horizontal control (NGRS) must be brought in to the stations of the Primary Control Network.
The vertical component of the PCN will be determined by differential leveling techniques. Benchmarks are required at 0.5 miles (0.75 km) intervals. A completed Department “Record of Control Sheet” in digital format and also manually recorded in Form D-428, as approved by the Departments District Survey Manager, must be prepared for each benchmark.
Differential Leveling - a geodetic level and wooden or invar rod(s) or fiberglass bar coded rods are required for differential leveling. Procedures are outlined in "Standards and Specifications for Geodetic Control Networks", by FGCS, for Third Order leveling shall be adhered to, with the exception that the level rod may be of wood, metal, or bar coded fiberglass construction, and must be not more than 12 feet (4 m) in length.
8.6 RTK SURVEYS - GENERAL
A. Real-Time Kinematic - Real-Time Kinematic (RTK) is a method of GPS surveying in real time using short (stop and go) occupations, while maintaining lock on at least 5 satellites. The method requires a wireless data link between the base/network and rover receivers.
B. Kinematic Control Point – These points are similar to topo points, however, the occupation times are much longer because these points will be used to control the survey (similar to a control traverse point for conventional 3D surveys, see Table 1.3.1, page A.1-11, and Table 1.3.2, page A.1-12). All Kinematic Control Points shall be occupied two or more times utilizing different satellite geometry if possible. Differential leveling shall be used to establish vertical control meeting the standards for 3rd order see Table 8.3.1., Page A8-8.
C. Topo Points – Are all the physical features which might affect the proposed design of the project. These points shall be collected in such a manner as to allow for a proper DTM to be generated. The suggested horizontal and vertical precision for this type of point is as follows: Horizontal 0.050 foot (0.015m) and Vertical 0.070 foot (0.020m). If design requires for a higher level of precision then this method shall not be used.
8.7 DELIVERABLES
Following is a list of the deliverables for the survey network, when GPS and differential leveling methods are used. Submit one copy of the following on CD in the formats listed below.
Report of survey, which includes the following items: A.8-10 (1) Narrative description of the project, which summarizes the project, conditions, objectives, methodologies, and conclusions.
(2) Discussion of the observation plan, equipment used, satellite constellation status, and observable recorded.
(3) Description of data processing performed. Note software used, version number, techniques employed including integer bias resolution, if applicable, and error modeling.
(4) Provide a summary and detailed analysis of the minimally-constrained and over- constrained least squares adjustments performed. List observations and parameters that are included in the adjustment. List absolute and standardized residuals, variance of unit weight, and relative confidence for the coordinate differences at the 95% confidence level.
(5) Identify any data or solutions excluded from the network with an explanation as to why it was rejected.
(6) Department “Record of Control Sheets” (Horizontal & Vertical – see Appendix C-3, C-4) will be provided in MS WORD for each permanent horizontal and vertical control station.
(7) Include a diagram of the project stations and control at an appropriate scale (an overall site map in MicroStation or other compatible format approved by the Department.)
(8) DGN and DTM files in MicroStation when applicable.
(9) Raw data and solution files in native format (Trimble or RINEX).
(10) Original Form D-428 field books.
Required Deliverables:
One (1) hard copy of the entire survey report.
Two (2) hard copies of the overall site map.
Two (2) digital CD’s of the entire survey report with the following specifications:
(1) Survey report in MS WORD (or compatible format.)
(2) Existing control in MS WORD (or compatible format.)
(3) Project coordinates in MS WORD and ASCII (or compatible format.)
(4) Record of Control Sheets in MS WORD (or compatible format.)
(5) GPS raw and solution files in Trimble or RINEX. (6) Overall site map in MicroStation (or compatible format.) A.9-1
CHAPTER 9
TERRESTRIAL LASER SCANNERS
9.0 INTRODUCTION
Laser scanners provide surveyors a tool to accurately measure complex objects quickly and efficiently and from a safe location. The object to be surveyed does not have physically occupied during data collection. This feature is excellent for surveying bridges, mechanically stabilized earth walls, heavily traveled highway surfaces and rock faces.
Terrestrial laser scanning (TLS) save field time completing complex, hard to access projects, however, data extraction and production of usable CADD-Digital Terrain Model (DTM) format products usually take considerable office processing time. Field to office processing man-hours increase with density of points and complexity of the feature or object being scanned.
9.1 TERRESTRIAL LASER SCANNERS
Stationary terrestrial laser scanning (TLS) is performed from a static vantage point on the surface of the earth. TLS for civil engineering projects typically use “time-of-flight,” “phase based,” or “waveform” technology to measure distances. The basic concept is similar to that used in total station instruments; using the speed of light to determine distance. However, there are significant differences in the laser light wavelength, amount and speed of point data collected, field procedures, data processing, error sources, etc. Laser scanning systems collect a massive amount of 3-dimensional raw data called “point clouds.”
Time-of-flight (or pulse based) scanners are the most common type of laser scanner for civil engineering projects because of their longer effective maximum range (~300 feet (100m) to ~3000 feet (1000m)) and data collection rates as high as 50,000 points per second. A time- of-flight laser scanner combines a pulsed laser beam, a mirror deflecting the beam towards the scanned area, and an optical receiver subsystem, which detects the laser pulse reflected from the target. Since the speed of light is known, the travel time of the laser pulse can be converted to a precise range measurement.
A phase based laser scanner uses phase-shift algorithms to calculate the range component described above instead of time of flight. Phase based laser scanners have a shorter maximum effective range ~80 feet (25 m) to ~250 feet (80 m) than time-of-flight scanners, but are higher precision at short range < 80 feet (25 m), and have data collection rates approaching 500,000 points per second.
Waveform processing, or echo digitization laser scanners use pulsed time-of-flight technology and internal real-time waveform processing capabilities to identify multiple A.9-2 returns or reflections of the same signal pulse resulting in multiple target detection.
9.2 COORDINATE SYSTEM
The raw data point cloud produced by a laser scanner may be geo-referenced to a known coordinate system. All points within the point cloud have X, Y, Z and intensity values. The positional error of any point in a geo-referenced point cloud is equal to the sum of the geo-reference and individual point measurement errors. If requested by the Photogrammetry & Surveys Section, DTM’s will be referenced to the PA State Plane Coordinate System, see Part A, Chapter 8, Section 8.2, C, Page A.8-4. In order to enable efficient processing of point clouds in MicroStation, the Z-axis will be defined as the vertical axis, unless otherwise stated.
9.3 HORIZONTAL/VERTICAL ACCURACIES
Horizontal and vertical accuracy requirements will be specified by the Department on a per project basis.
9.4 POINT DENSITY and MEASUREMENT PRECISION
Point densities should be equal in both scanning axes. Point density during the scanning process will depend upon the range to an object. It is not, therefore, currently possible to maintain a constant point density over an entire subject during the scanning process. Typically, a particular object or surface will be of interest (i.e. bridge, rock face) therefore, a regular density of points is preferable. Point density specified is a maximum.
Required accuracy and point density will be stated in the project scope. This will be defined by a survey scale or based on a minimum feature to be discernable in the point cloud.
The beam width of the measurement beam must not be greater than double the effective point density.
All reference to point density will be provided as the average 3D distance between points at a defined range.
9.5 OVERLAPPING SCANS
Areas of overlapping scan data will be filtered to reduce the point density in the final registered point cloud to reduce file size and improve software performance/data handling during processing.
9.6 DATA VOIDS
Data voids should be minimized during the scanning process by preplanning the selection of appropriate scanning positions, scanning under appropriate weather conditions, and A.9-3
using multiple scans. Data voids due to temporary obstructions, such as passing vehicles and pedestrians, should be limited by appropriate positioning of the scanner.
9.7 TARGETING
If requested by the Photogrammetry & Surveys Section, targeted points will be in the PA State Plane Coordinate System. Targets will not be positioned, or be so large, that they obscure important details of the subject. Targets mounted to the surface of the subject must be fixed in a manner that does not damage the surface.
A. Registration
The collected point clouds must be transformed to the local site coordinate system. The residuals of the registration process must be shown to be equal to or better than the geometric precision required by the end deliverable. The process of registration can be performed using four methods:
Where registration is done solely via a resection calculation: Each scan must contain a minimum of 4 appropriately distributed XYZ control points/targets. The residuals of the registration process and the geometric precision of the estimated parameters should be noted in the survey report.
Where registration is done using a known station position and orientation: The data must include 3 appropriately distributed XYZ control points per scan. The residuals of the registration process and the precisions of the estimated parameters should be noted in the survey report.
Where registration is performed using surface matching techniques: The data must include at least n + 3 appropriately distributed XYZ control points/targets, where n is the number of scans made. The residuals of the registration process and the precisions of the estimated parameters should be noted in the survey report. The geometric accuracy of the fit should be noted in the survey report.
A combination of the previous methods may be used to improve the speed and ease of the registration process.
State of the art TLS systems allow occupation of known survey control points and backsighting to other known survey control points as a method of registration.
B. Supporting Imagery
At each setup, image data to show the location of the scanner and the subject being scanned. A.9-4 This imagery should be of a high resolution and clearly portray the subject in question.
9.8 WEATHER
Scanning and image capture may not be performed in adverse weather conditions where the quality of observed data would be affected. For example, scanning in heavy rain may cause data voids due to erroneous data points caused by returns from airborne raindrops or erroneous range measurement due to refraction of the measurement beam.
9.9 DELIVERABLES
A. Survey Material Deliverables
The following will be required in digital format, unless otherwise requested in the project scope of work: Project metadata. Raw scan data in its original format. Scan metadata. Control information. Registration information for all raw scans to the site coordinate system. Images of scanning scenes. Registered scan data in its original format.
A hard copy survey report will be required containing: Witness/illustrative diagrams outlining the position of scan stations and control points. Details of the traverse/control network, a list of the 3-dimensional positions of all control points and residuals for the computed XYZ control. Precision of any parameters derived in the registration process for each scan along with the residuals of the registration. A summary outlining the completeness of the point cloud and all known data voids. All site sketches and additional field notes
B. Project Deliverables
Project deliverables will be defined for each project. Deliverables will be Micro Station or equivalent software format and may include contours, cross-sections, profiles or the actual point cloud data.
Scan Metadata
Metadata (information relating captured information) is required with all raw scan data and scan projects to be archived by PSS. Metadata will be provided in both hardcopy and digital format may include the following: File name of the raw data. Date of capture. A.9-5
Scanning system including manufacturer’s serial number. Company name. Project description. Scan number. Total number of points. Point density on object (with reference range). Weather conditions during scans. File name of an image, located at the point of collection, showing the data collected (filename must be the same as the filename of the raw data file).
Project Metadata
Project metadata to be archived by PSS may include the following: Filename(s) of the raw data used in the registration. Date of capture. Scanning system(s) used including manufacturer’s serial number(s). Company name. Project description. Number of individual scans. Scan numbers of all scans. Total number of points. Filename of the control data. Description of registration method (e.g. All scans registered to local site grid using targeted points). An index plan showing the data collected with the individual scan locations shown and named. Weather during survey. Any scanner specific information.
PART B - PHOTOGRAMMETRIC MAPPING
TABLE OF CONTENTS
CHAPTER SUBJECT PAGE
CHAPTER 1 PROJECT DEVELOPMENT
1.0 .... INTRODUCTION ...... B.1-1 1.1 .... AERIAL PHOTOGRAPHY AND TOPOGRAPHIC MAPPING ...... B.1-1 1.2 .... AREA ...... B.1-1 1.3 .... GUIDELINES FOR REQUESTING SERVICES AND PROJECTS . ... B.1-2 A. Contact Prints ...... B.1-2 B. Digital Imagery…...... B.1-2 C. Photo Enlargements ...... B.1-2 D. Oblique Photography ...... B.1-3 E. Planimetric Maps...... B.1-3 F. Topographic Maps…...... B.1-3 G. Digital Orthophotography ...... B.1-3
CHAPTER 2 AERIAL PHOTOGRAPHY ACQUISITION
2.0 .... INTRODUCTION ...... B.2-1 2.1 .... FLIGHT HEIGHT ...... B.2-1 2.2 .... VERTICAL AERIAL PHOTOGRAPHY ...... B.2-1 A. Areas to be Photographed...... B.2-1 B. Coordination of Mapping Photography with Ground Targeting ...... B.2-2 C. Aircraft…………… ...... …..B.2-2 D. Camera ...... B.2-3 E. Airborne GPS...... B.2-3 F. Aerial Film ...... B.2-3 G. Digital Photography ...... B.2-4 H. Photography…...... …… ... B.2-5 2.3 .... PHOTOGRAPHIC MATERIALS TO BE DELIVERED ...... B.2-6 A. Contact Prints ...... B.2-6 B. Digital Imagery ...... B.2-6 C. Photo Indexes...... B.2-7 D. Aerial Film………………………………………………………… B.2.7 E. Flight Navigation Data……………………………………………... B.2.7 F. Airborne GPS Data………………………………………………… B.2.7
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CHAPTER SUBJECT PAGE
CHAPTER 3 TARGETING AND CONTROL SURVEY
3.0. ...INTRODUCTION...... B.3-1 3.1. …TARGETING ...... B.3-1 3.2. ...CONTROL SURVEYS - GENERAL ...... B.3-4 A. Standards and Specifications ...... B.3-4 .B. Classification of Accuracy ...... B.3-4 .C. Datums ...... …..B.3-7 3.3. ...GLOBAL POSITIONING SYSTEM ...... B.3-7 A. Carrier Phase Tracking ...... B.3-7 B. Code Tracking ...... B.3-8 C. GPS Techniques ...... B.3-8 D. Redundancy ...... B.3-8 E. Specifications ...... B.3-8 F. Network Design ...... B.3-9 G. Least Squares Adjustments ...... B.3-9 3.4. ...TRAVERSE METHODOLOGY ...... B.3-9 A. Angles and Azimuths ...... B.3-9 B. EDM Distances ...... B.3-11 C. Eccentric Observations ...... B.3-12 3.5. ...PRIMARY CONTROL NETWORKS ...... B.3-12 3.6. ...MAPPING CONTROL SURVEYS ...... B.3-14 A. Horizontal...... B.3-15 B. Vertical ...... B.3-15 C. Airborne GPS……………………………………………………… ..B.3-17 3.7. ...DELIVERABLES ...... B.3-17
CHAPTER 4 ANALYTICAL AEROTRIANGULATION
4.0. ...INTRODUCTION...... B.4-1 4.1. ...ANALYTICAL AEROTRIANGULATION ...... B.4-1 A. Measuring for Analytical Triangulation ...... B.4-1 B. Accuracy ...... B.4-1 C. Supplemental Control ...... B.4-2 D. Interval of Supplemental Control Spacing on Aerial Photography ....B.4-2 E. Measurement Corrections ...... B.4-2 F. Photography Strip Ties ...... B.4-2 G. Point Labeling ...... B.4-3 H. Software and Process ...... B.4-3 I. Reports and Records ...... B.4-3
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CHAPTER SUBJECT PAGE
CHAPTER 5 DIGITAL MAP COMPILATION
5.0 ... INTRODUCTION ...... B.5-1 5.1 ... COMPILATION ...... B.5-1 A. CADD File Creation ...... B.5-2 B. Image Scanning ...... B.5-2 5.2 ... MAP CONTENTS ...... B.5-2 A. Matches ...... B.5-2 B. Control Stations ...... B.5-2 C. Planimetry ...... B.5-3 D. Digital Terrain Models and Topography ...... B.5-4 E. Obscure Areas (with data)…………… ...... B.5-4 F. Obscure Areas (without data) ...... B.5-5 G. Symbols, Names, and Graphic Quality ...... B.5-5 H. Index Map ...... B.5-5
CHAPTER 6 DIGITAL ORTHOPHOTOGRAPHY
6.0 ... INTRODUCTION ...... B.6-1 6.1 ... ORTHORECIFICATION ...... B.6-1 A. Aerial Photography ...... B.6-1 B. Ground Control ...... B.6-1 C. Aero Triangulation Solution ...... B.6-1 D. Scanning…………...... B.6-1 E. Digital Image Files ...... B.6-2 F. Accuracy…...... B.6-2 G. Image Quality……...... B.6-2 H. Digital Terrain Models (DTM)...... B.6-2 I. Format…………………………………………………………… B.6-2
CHAPTER 7 DIGITAL MAPPING ACCURACY TESTING
7.0 ... INTRODUCTION ...... B.7-1 7.1 ... ACCURACY ...... B.7-1 A. Horizontal Accuracy ...... B.7-1 B. Vertical Accuracy ...... B.7-2 C. Lower Accuracy Maps ...... B.7-2 7.2 ... MAP ACCURACY TEST ...... B.7-2
CHAPTER 8 ELECTRONIC MEDIA PREPARATION AND ARCHIVING
8.0 .. INTRODUCTION ...... B.8-1 8.1 .. ELECTRONIC FILE TRANSFER ...... B.8-1 8.2 .. ELECTRONIC FILE ARCHIVING...... B.8-1
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B.1-1
CHAPTER 1
PROJECT DEVELOPMENT
1.0 INTRODUCTION
This chapter outlines specific products, services, standards and procedures when using aerial photography and photogrammetry. The products and services described have specific uses during preliminary, final design and construction phases. The District Chief of Surveys or District Photogrammetry Coordinator is the vital link in determining when aerial photography and photogrammetric techniques are appropriate verses using field survey techniques. The Photogrammetry and Surveys Section will provide man-hour/cost estimates, project schedules, and recommendations on products to be considered for mapping projects. Even if photogrammetric mapping is not required for the project, the project manager may want to consider obtaining aerial photography for displays, public meetings and project planning.
1.1 AERIAL PHOTOGRAPHY AND PHOTOGRAMMETRIC MAPPING
Photogrammetric mapping is prepared for highway projects at a scale of 1”= 200’ (1:2000) for preliminary design, and 1”= 50’ (1:500) for final design. Mapping will conform to requirements established in this manual. Maps for preliminary engineering and environmental studies are normally produced at 1”= 200’ (1:2000) with 5 feet (1.0 m) contours. Maps for final design purposes are compiled at large scale of 1”= 50’ (1:500) with a contour interval of 1 foot (0.25 m).
Projects requiring higher accuracy may be satisfied using low altitude photogrammetry. Altitudes above mean terrain as low as 300 feet (90 m) can be accomplished using helicopters and achieve accuracies to 0.05 foot (0.015 m) horizontal and 0.03 foot (0.009 m) vertical. Low altitude photogrammetry is more costly than fixed wing methods but usually less expensive than conventional survey methods. It also eliminates most safety concerns present using field survey techniques.
Photogrammetric mapping may be customized to meet any projects needs. Unique scales may be requested. In applications where accuracy is not as important, Airborne GPS may be used to eliminate costly ground control. Coordinate with your Chief of Surveys and with the Photogrammetry and Surveys Section to customize the photogrammetric mapping products for your project.
1.2 AREA
The area to be mapped will be delineated on a project map (quadrangle) and sent electronically to the Photogrammetry and Survey Section. Any changes to the area while mapping is in progress will also be submitted as a supplement to the project map. Proper planning is vitally important to assure the project is fully covered by the initial aerial photo mission. Should B.1-2
additional photography be required, a time lapse of several months may occur until proper ground conditions exist for the reflight.
1.3 GUIDELINES FOR REQUESTING SERVICES AND PRODUCTS
Obtain a photogrammetric request form from the District photogrammetry coordinator, survey manager, or the Photogrammetry & Surveys Section. Complete the form and return it to the Photogrammetry & Surveys Section along with a copy of a U.S.G.S. map with the mapping limits delineated. Project managers should be aware of limited flying seasons in spring and fall and complete the photogrammetric request forms early in the project planning phase.
Flights may be conducted year round, however, mapping projects resulting from winter or summer photography could be lower quality and have large areas obscured by vegetation or snow.
A wide variety of products and services are available, ranging from a single vertical 9”x 9” aerial photograph, oblique photography, to a complete digital topographic map and digital orthophotography. These products provide critical time sensitive information to improve project planning and design of highway projects. Contact the District photogrammetry coordinator, survey manager, or the Photogrammetry & Surveys Section for assistance in determining the best products for the project.
A. Contact Prints. A contact print is a direct positive copy developed at the same scale as the aerial negative. They are usually printed on resin coated paper in color, color infrared, or black & white.
B. Digital Imagery. Aerial negatives are scanned using a precise, high resolution aerial film scanner. The digital files are then roughly oriented to the ground. A low resolution copy is made without ground orientation and may be useful in presentations or documents. High resolution imagery can be opened with MicroStation or software provided by the Photogrammetry & Surveys Section. When opened in MicroStation, its position will be correct to within a few hundred feet. For more accurate geographic referencing, see Section G. “Digital Orthophotography” below.
C. Photo Enlargements. A photo enlargement is a print of an original aerial negative produced at a larger size and scale. These can be whole or partial photo images of the original aerial negative. Photo enlargements are printed on resin coated paper, or film media.
These products may be enlarged or scaled to an existing map (i.e. US Geological Survey (USGS) Quad Map, etc.) or to known ground distances. However, photo enlargements will still contain distortions caused by tip and tilt of the aerial camera at the instant of exposure. Additional distortions will also be caused as a result of image displacement detected from the point of perspective caused by terrain relief. These distortions affect B.1-3 accuracy of ground distances calculated from scaled photo distances.
D. Oblique Photography. Oblique photography is used to obtain a panoramic view of the project. Usually oblique photography is taken with a handheld digital camera. However, for special applications, the aerial camera can be used to obtain a very high resolution oblique. Obliques are used for an overall project view for use in planning and at public meetings. It is also used for change detection or construction monitoring. The photography can be enlarged to meet project needs.
E. Planimetric Maps. A planimetric map is a cartographic product that depicts culture and man-made elements. These elements also include ground cover, such as wooded areas, brush or cultivation and bodies of water, like streams, rivers, or lakes. Planimetric maps do not include contours, Digital Terrain Models, or other elevation information.
F. Topographic Maps. A topographic map is a cartographic product that depicts culture and/or man-made elements along with detailed and accurate elevation information presented in the form of contours and spot elevations. Digital Terrain Models (DTM’s) are used in the generation of contours, profiles, and cross-sections. DTM’s consist of breaklines (a line depicting a major change in contour direction) mass points (random spot elevations) and spot elevations (high and low points in the terrain). DTM’s can also be used to compute volumetric quantities.
G. Digital Orthophotography. Digital orthophotography is aerial imagery that has a photogrammetric orientation applied in order to remove known camera errors and account for platform orientation and relief displacement. The resulting imagery has the same properties as a map. Digital orthophotography meets the same accuracies as vectorized topographic maps as outlined in Chapter 3 - Targeting and Control Survey, Section 3.2 – Control Surveys – General. The orthophoto process requires topographic map data. However, when orthophotography utilizes topographic map data already produced for the project base map, the cost for orthophotography is low. Orthophotography will add approximately 10% to a project that already includes a topographic base map.
The actual orthorectification is carried out using softcopy workstations. These workstations produce a scaleable digital image of the original photograph. Orthophotography is produced at the required scale, free of distortions, depicting orthogonal projection of the photo image. The pixels are shifted to their correct spatial location on the datum plane. The final product is an orthogonal, distortion free image saved in electronic format and/or plotted on hard-copy materials.
A combination of digital orthophotography with DTM data and/or planimetry may also be requested. These products are useful for preliminary studies and planning purposes. They offer visual image information provided by a photograph, accuracy (at ground level) of a photogrammetrically compiled vector map, and elevation and slope data derived from the DTM data. B.2-1
CHAPTER 2
AERIAL PHOTOGRAPHY ACQUISITION
2.0 INTRODUCTION
Requirements outlined in this chapter are applicable to aerial photography for both mapping and non-mapping uses.
2.1 FLIGHT HEIGHT
Aircraft flight height for each photography mission is dependent upon the scale of mapping and contour interval required for the project. Flight height for mapping photography will adhere to requirements established in Table 2.1.1.
Table 2.1.1 Flight Height Requirements for Mapping Projects
SCALE OF CONTOUR SCALE OF MAX FLIGHT MAPPING INTERVAL PHOTOGRAPHY HEIGHT ABOVE feet (m) feet (m) (MAXIMUM) MEAN TERRAIN feet (m)
1”=200’ (1:2000) 5 (1.0) 1:12000 6000 (1800)
1”=100’ (1:1000) 2 (0.5) 1:6000 3000 (900)
1”=50’ (1:500) 1 (0.25) 1:3000 1500 (450)
Flight heights for photo only projects vary according to the limits of desired coverage and/or degree of detail and resolution required.
2.2 VERTICAL AERIAL PHOTOGRAPHY
A. Project Planning. Requests for mapping or photo-only projects will include a U.S. Geological Survey (USGS) 7 ½ minute quadrangle map with the area to be photographed or mapped delineated along with a current Photogrammetry and Surveys Section request form.
When the request is received, photo mission planning is normally performed by the Department but may also be done by the Department’s business partners.
With the advent of GPS flight navigation systems, project planning and acquisition can be done with greater accuracy. Because of the time and cost savings that are realized from implementing these systems, it is recommended that a flight management system be utilized B.2-2 on all Department projects. The following guidelines will be adhered to when planning projects using a computer and then importing the planning data into a flight management system. 1. Planning will be done utilizing digital map software that is designed to facilitate aerial photo planning. 2. Projects to be flown at 6000 feet (1800m) should be planned utilizing a USGS 7 ½ minute quadrangle map or better with a digital elevation model to ensure photo centers will be planned taking into account terrain differences. 3. The planning will be viewable or printable utilizing a USGS topographic base map. It is recommended to have the project display on an aeronautical chart base map. 4. The planning will include the following visual elements: a. Project identification consisting of County, State Route, and Section. b. Any additional project information required. c. Number of flight lines and photos. d. Aircraft altitude above mean sea level. e. Delineated photo coverage and area to be mapped (if applicable). f. Flight line(s) including line number annotation. g. Pre-planned photo centers and outlines of the individual photo coverage. h. Planned ground target locations. 5. Planning will include an export file containing coordinates of pre-determined photo centers and pertinent flight data required by the specific flight navigation system. 6. If ground targeting is required, include a separate export file containing the coordinates for target locations. 7. When using airborneGPS control, care must be exercised when planning the project. AirborneGPS technology does not lend itself well to linear strip photography/mapping, so projects must be planned with block coverage of the area. Addition of cross flights at either end of the block (and intermediate cross flights for large projects) are required to tie the GPS data into a unit that can have a combined block adjustment applied, if necessary. 8. An after mission report, including actual photo center coordinates and flight heights, is to be provided by the Department and may be required from business partners.
B. Coordination of Mapping Photography with Ground Targeting. The flight map will indicate all ground targeting requirements. All photographic flights will be coordinated with the placement of the targets in order to minimize time between operations and possible destruction of targets. A digital file with panel location coordinates in the appropriate state plane system will be provided and included with the photo mission planning.
C. Aircraft. Aircraft used for the photography work will be maintained and operated in accordance with regulations of the Federal Aviation Administration (FAA) and the Civil Aeronautics Board. Aircraft will have a service ceiling with an operating load (crew, camera, film, oxygen, and other required equipment) of not less than 18,000 feet (5500 m) B.2-3 above mean sea level. The aircraft will have performance capabilities for safe flight at the lowest altitudes permissible within FAA regulations while still maintaining a ground speed slow enough to expose photography free of detectable image motion. Aircraft will also contain the appropriate avionic equipment to operate in positive control areas.
D. Camera. Photography will be taken with a precise aerial camera having a nominal focal length of 6” (153 mm) with a 9” x 9” (230 mm x 230 mm) negative. The aerial camera must meet the criteria as defined in USGS’s “Aerial Camera Specifications.” An approved United States, Department of the Interior, Geological Survey, and Calibration Report must be submitted to the Department. The report must be dated within the last three years. Digital cameras are acceptable with pre-approval by the Department.
E. Airborne GPS. When utilizing airborne GPS control, the following conditions must be met: a. A survey grade GPS receiver capable of logging one-half second data epochs, as well as a reference for the mid-exposure pulse of the camera will be connected to or incorporated into the camera/flight management system. b. The offset distance (x, y, z,) from the center of the film plane to the phase center of the GPS antenna must be accurately calculated with the camera mount in the null position (0.0º roll, pitch, and yaw). Most post-processing programs allow for separate data entry of the offset distance, inter-nodal distance and the focal length of the camera. These values must be known and used in the post processing solution. There should also be a means of recording the gyro-stabilized mount vectors at the mid-exposure pulse (MEP). c. When the actual photo flight occurs, raw data logging should begin no less than five (5) minutes prior to the first exposure and continue without interruption until no less than five (5) minutes after the last exposure on the project has been acquired. d. If possible, while the base receiver (or CORS site) and the receiver in the aircraft are both logging GPS data, the aircraft should fly over the ground reference station prior to starting the project and upon completion of the image acquisition. Many times this can be incorporated with complying with guideline “c.” e. While flying the photo mission, the bank angle of the aircraft should be limited to avoid losing lock with the GPS satellites and degrading the accuracy of the calculated position. f. When possible, the satellite coverage should be evaluated prior to flying the project and the flight time adjusted to provide the best satellite position geometry available.
F. Aerial Film. Photography will be taken using only fresh, fine grained, high-speed aerial photographic emulsion on a stable polyester film base. The Department standard for photography is Eastman Kodak Aerocolor III type 2444 or equivalent. Projects requiring color infrared imagery, Kodak Aerochrome infrared type 1443 or equivalent are recommended. Negatives should be clear and sharp in detail and should be free of clouds and cloud shadows, smoke, haze, snow, light, streaks, static marks, excessive shadows, tears, scratches, and other B.2-4 blemishes which would interfere with their intended purposes.
To ensure uniform gradation and density, the negative should meet the following guidelines: Average minimum image densities should be 0.30 above gross fog, with no area measuring less than 0.15 above gross fog. Density ranges of the negatives should be between 0.8 and 1.5. High altitude negatives may be slightly lower to allow for the effect of partial integration of the measuring device. Density range measurements should be taken with a transmission densitometer using an aperture of no greater than 0.06’ (2 mm).
To insure dimensional stability, the film should not be stretched or deformed in any way. It should not be subjected to extreme changes in humidity and temperature. The film will be sealed in its container and stored at a temperature recommended by the manufacturer at all times, except when in actual use during the flight mission or when being processed.
Special care will be exercised to insure the proper development of and the thorough fixing and washing of the exposed film. To provide archival quality, rolling the film too tightly on spools during processing and drying should also be avoided.
G. Digital Imagery. Digital imagery, whether captured by digital camera or scanned shall be delivered to the Department on DVD or portable hard drive.
Scanned imagery: When scanned imagery is requested, great care will be taken to protect the original film which will be added to Department archives. The film may not be cut and scratches must be avoided. The film must be cleaned to remove foreign particles prior to scanning. Normally, 14 or 15 micron scans will be requested.
For mapping projects, minimal post processing will be performed in order to preserve as much radiometric data as possible. When the digital imagery is the final product or will be used to make enlargements, post processing for best clarity, color, contrast and balance shall be performed.
Digital imagery: When imagery is captured with a Department approved digital camera, it must be post- processed into final deliverable frames to be delivered on DVD or portable hard-drive. It must be color balanced as outlined above. Metadata files must be included. Camera information, date and time of capture, geographic position and camera settings must be included at a minimum.
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H. Photography. All deviations in flight height will be within 5% of the specified values discussed in Section 2.1 - Flight Height. During inspection, flight altitude will be checked by a film negative distance to ground distance comparison. The points used for this comparison should be as near as possible to the mean ground elevation of the flight line being checked.
Each flight line will track the alignment plotted on the flight map within a ground distance that is no more than 10% of the flight height above mean ground elevation, as specified in Section 2.1 - Flight Height.
Each flight strip will be photographed so that the principal points of the first two and last two exposures fall outside the boundaries of the specified photography coverage area. If project requirements dictate a single stereo pair with the photo center positions predetermined, then the additional two photos at each end will not be required.
1. Time of Photography. Photography will be taken only when light and atmospheric conditions are satisfactory for producing negatives that will meet specifications. Photography for mapping will normally be taken mid-day when the solar angle is equal to or greater than 30 degrees. However, under certain conditions and types of terrain, acceptable photography can be obtained when the solar angle is less than 30 degrees. Areas with predominate steep, wooded slopes facing West, Northwest, North, Northeast, or East will be photographed at the time of day when the sun's angle provides the optimum illumination of the project area. All photography for mapping will be taken when the ground is clear of snow and trees are foliage free. 2. Forward Overlap. The forward overlap for each flight line will average 60%, 2%. Overlap of any two consecutive exposures of less than 55% or more than 65% may be cause for rejecting that flight line in total. In some instances, because of terrain or other special factors, the average overlap may not meet the specific requirements established. If so, this information will be recorded on the project flight map. 3. Side Lap. The side lap of parallel lines of vertical aerial photography will average 30%, 10%. Any exposure not meeting this criterion may be cause for rejecting that flight line. 4. Crab. The crab of all photographs for a flight line will not exceed an average of 3 degrees. Crab of two or more consecutive photographs exceeding 5 degrees may be cause for rejecting that flight line in total. 5. Tilt. Special care should be taken to minimize tilt. A gyro-stabilized mount should be utilized, if available. The tilt of all photographs for a flight line will not exceed an average of 1 degree. The tilt of any single photograph exceeding 3 degrees may be cause for rejecting that flight line in total. 6. Image Motion. Care must be taken to eliminate image motion. Many cameras now incorporate Forward Motion Compensation (FMC) and gyro-stabilized mountings to eliminate image motion. While a project flown without either or both of these is not reason for rejection, projects with image motion will be rejected by the Department. 7. Titling. All photography must include annotation of pertinent data as described below. B.2-6
This information may be place on the edge of the negative by the camera system at the time of acquisition or it may be added to the imagery after the film is processed. All aerial photographs of each flight strip will be identified as indicated by the following sample information: Date Time of Exposure Nom. Scale Focal Length Latitude Longitude SR # 3/15/01 12:00:00 1:3000 153.00 395857.4N 761507.5 W 0030 Flight & Photo # 001-001
The flight strip numbers will be in a continuous numerical sequence but photo numbers will start at 001 for each new flight strip. Each individual flight strip will be identified with a flight number. The first flight strip will be labeled as "flight 001.” All flight strips following "flight 001." will be labeled numerically in ascending order. Therefore, the last flight number is the same as the total number of flights covering the project area. Photographs will be numbered in a sequence to begin new for each flight strip, beginning on "flight 001" with "exposure 001." For example, flight strip identification would be as follows: Flight 001, Exposures 001 through 012 Flight 002, Exposures 001 through 099 Flight 003, Exposures 001 through 101, etc.
Numbering of flight strips and exposures will originate at the western or southern end of the project. Automated camera annotation is acceptable, if it meets the criteria outlined above. If automated camera annotation is not available, manual annotation of the photography data will be placed on the eastern and/or northern edges of the aerial film negatives.
Film negatives of project photography will be delivered on metal spools in suitable containers. These containers will be labeled on the outside. The label will show route number, section number, county, photography scale, date of photography, number of flight lines, and the number of photograph exposures.
2.3 PHOTOGRAPHIC MATERIALS TO BE DELIVERED
A. Contact Prints. Three (3) sets of contact scale prints of all exposures approved as project photography will be produced and delivered. All three (3) sets will be prepared on medium weight, semi-matte, RC (resin coated), commercial paper. All contact prints will be trimmed to include the entire image frame, as well as annotation that would be put on by the camera system during exposure. Special care will be taken to preserve all camera fiducial (reference) marks on the prints.
B. Digital Imagery. Scanned aerial film, original digital vertical photography and/or oblique imagery will be delivered on CD, DVD or portable hard drives. For high resolution imagery which can’t be opened with normal desktop software, a free viewing software will B.2-7 be included. Also included with delivery is the current README! File from the Department which includes instruction for proper use.
C. Photo Indexes. All photo projects will require two (2) sets of photo indexes. Size, scale, and type will be determined by the Department on a per project basis. Photo indexes may be prepared by photographic methods or by means of a computerized flight navigation system. If indexes are photographically prepared, original film negatives must be sent to the Department.
D. Aerial Film. All original aerial film flown for the Department will be delivered to the Department upon completion of production of requested photo products.
E. Flight Navigation Data. An export file that includes the taken photo center coordinates, along with other available data (i.e. flight path, gyro-mount vectors, photo annotation, deviation from planning, etc.).
F. Airborne GPS Data. If Airborne GPS is utilized when flying a project, the following data in electronic file format must be included: a. GPS Raw Data files (base and aircraft receivers). b. GPS Rinex files (base and aircraft receivers). c. Event file (Mount vectors and mid exposure pulse) from the aircraft. d. Text file of additional data (loss of satellite lock, etc.) from the aircraft. e. Measured antenna offset with camera mount at null position. f. Inter-nodal camera distance. g. USGS camera calibration report.
B.3-1 CHAPTER 3
TARGETING AND CONTROL SURVEY
3.0 INTRODUCTION
Targeting operations are an essential part of photogrammetric mapping to be considered prior to establishing a control survey. The first section of this chapter deals with pre-flight targeting operations and field control requirements for analytical aero-triangulation. The remainder of the chapter deals with control survey standards, specifications, and accuracy requirements for all photogrammetric mapping projects.
3.1 TARGETING
Pre-flight targeting is performed to make visible on the photographs ground locations of control points to be surveyed and measured during the analytic process. Highway design mapping often requires careful pre-flight planning for optimal target placement. To reduce the possibility of pre-targeted points being moved or lost prior to the aerial mission, it is important to schedule field placement as close as possible to the anticipated flight. Should an extensive delay occur between target placement and the flight, then it may be necessary to revisit the targeted points to check their condition. Targets should be located where visibility will be assured on the photography. Pre-targeting layouts must be approved by the “Photogrammetry & Survey Section prior to placement.”
The use of Global Positioning System (GPS) must be considered during targeting operations. GPS requires an open view of the sky, especially towards the south. When a selected location is obstructed, it is often possible to move it to a nearby location without adversely affecting map accuracy. Accessibility for surveying, especially GPS, must be considered. When placing targets or survey stations on private property, a "Notice of Intent to Enter" (R/W983) will be prepared and mailed to any affected property owners by the District office. This notice will alert the property owner that PennDOT employees and/or their consultants, may need to enter their property to conduct survey work. Specific requirements are outlined in Section 409 of the "Eminent Domain Code,” dated September 1, 1964. All policies and procedures will be in accordance with Design Manual, Part 1.
Photographic targets of symmetrical shape, size as shown in Figure 3.1.1, appropriate photographic contrast and resolution will be placed on the ground, centered on the station markers of all National Geodetic Survey (NGS) / US Coast and Geodetic Survey (USC&GS) horizontal and vertical control points within the project photo coverage area. Targets will also be placed on all survey control points for which X, Y, and Z coordinates are known or are going to be established. These target locations will allow analytical aero-triangulation to be accurately accomplished. Figure 3.1.1 indicates recommended dimensions and patterns for photographic targets at the various negative scales. Figure 3.1.2 represents the minimum pattern of control placement for both single strip flying and block photography. Additional horizontal and vertical control will be established as outlined in other portions of this manual. B.3-2
CONTROL POINT TARGETS
PREFERRED ACCEPTABLE ACCEPTABLE
TEST POINT TARGETS
RECOMMENDED TARGET SIZES
T, inches (mm) L, feet, (m) NEGATIVE WIDTH OF LEG LENGTH OF LEGS SCALE (TIP TO TIP)
< 1:3000 3 (75) – no X or T 1 (0.3) – no X or T 1 : 3000 6 (150) 6 (2) 1 : 6000 6 (150) 12 (4) 1 : 12000 12 (300) 15 (5)
Figure 3.1.1 Recommended Target Sizes B.3-3
SINGLE STRIP
BLOCK
Figure 3.1.2 Minimum Field Control Requirements for Analytic Aero-Triangulation
B.3-4 3.2 CONTROL SURVEYS – GENERAL
Control established for photogrammetric mapping projects consists of two separate tasks: Primary Control Networks and Mapping Control/Map Testing Surveys. All control surveys will be based on National Geodetic Reference System (NGRS) stations. Global Positioning System (GPS) is required for Primary Control Networks and recommended for Mapping Control Survey/Map Testing Surveys.
A. Standards and Specifications. Federal Geodetic Control Committee (FGCC) publishes standards and specifications for geodetic control surveys in the United States. The documents pertaining to geodetic control surveying are listed below in Table 3.2.1 and are to be used by the Department and its consultants when finalized and deemed necessary.
Table 3.2.1 Standards and Specifications References
Agency Publication Pub 122M Reference
FGCC Standards and Specifications for Conventional traverse / Geodetic Control Networks differential leveling
FGCC Geometric Geodetic Accuracy GPS surveys (static) Standards and Specifications for Using GPS Relative Positioning Techniques
FGCC Geospatial Positioning Accuracy GPS surveys (static) Standards, Part 2: Standards for Geodetic Networks
NGS User Guidelines for Single Base Real GPS surveys (real-time network) Time GNSS Positioning
B. Classification of Accuracy. A horizontal control survey is classified by the “Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques” from the FGCC, as meeting a given accuracy standard when the propagated relative error at the 95 percent (two-sigma) confidence level, for all station pairs, is less than the maximum allowable error, s, for the Order of accuracy specified for the project. Maximum allowable error, s, is computed as:
US Survey Feet s = 0.033 (32.81e )2 +( 0.16 pd )2 Metric s = 0.01 ( 0.1e )2 +( 0.1pd )2 where s = maximum allowable one-dimensional error in feet (meters) at the 95 percent (two-sigma) confidence level d = distance in miles (kilometers) between any two stations B.3-5 p = the line length dependent geometric relative positioning accuracy standard in parts per million (ppm) e = base error in hundredths of a foot (millimeters) (this includes station dependent setup errors)
Table 3.2.2 lists the values of p and e for the different Order classifications applicable for Department work. Table 3.2.2 e and p Values
GROUP ORDER CLASS e feet (mm) p (ppm)
C 1 0.03 (10) 10 C 2 I 0.06 (20) 20 C 2 II 0.10 (30) 50 C 3 0.16 (50) 100
Table 3.2.3 FGCC/NGS Horizontal Accuracy Conversion Chart (Department derived)
FGCC FGCC 95% NGS Stated Accuracy NGS - PennDOT Accuracy Confidence feet (cm) Accuracy Class Designation feet (m) Class Designation 1-Millimeter 0.003 (0.001) 0.003 (0.10) AA 2-Millimeter 0.01 (0.002) 0.01 (0.20) AA 5-Millimeter 0.02 (0.005) 0.01 – 0.02 (0.21 – 0.50) A N/A 0.02 – 0.03 (0.51 – 0.99) B 1-Centimeter 0.03 (0.010) 0.03 – 0.07 (1.00 – 1.99) 1 2-Centimeter 0.07 (0.020) 0.07 (2.00) 2-I N/A 0.07 – 0.16 (2.01 – 4.99) 2-II 5-Centimeter 0.16 (0.050) 0.16 (5.00) 3
For a GPS network, the propagated relative error will be computed using a least squares adjustment for all three dimensions (X, Y, and Z or N, E, and U) with a 95 percent (two- sigma) confidence criteria. Accuracy classification of a GPS relative positioning survey may be determined in one of two ways, dependent upon the project classification. A "geometric" classification may be made where the confidence tests are imposed upon a minimally constrained (free) least squares adjustment independent of the local geodetic reference system external control. Geometric classifications are applicable to project specific control systems such as those developed for specialized design surveys and monitoring networks. The second method for classifying GPS relative positioning surveys is an "NGRS" classification determined from a least squares adjustment constrained to the local geodetic reference system, holding the external control fixed. This method is a good measure of the accuracy of a network when the local geodetic reference system is of higher accuracy than the new B.3-6
observations (i.e. when a statewide HARN is used.) Advances in GPS technology have provided new systems to be used in addition to traditional NGRS concrete monuments. NGRS permanently mounted GPS antennae, such as Continuously Operating Reference Stations (CORS) and virtual reference systems (VRS – a network of CORS with real-time kinematic capability), are now augmenting for and with traditional monumentation.
While a least squares adjustment is preferred, simple traverse lines may be adjusted using the compass rule or other error distribution methods.
Accuracy classification from the “Standards and Specifications for Geodetic Control Networks” from the FGCC, for differential leveling is expressed as follows: US Survey Feet e = 1.609M Metric e = k where e is the allowable error in feet (meters) for a level run of M (miles) or k (kilometers) in length, and μ is a factor, which depends on the Order of accuracy, desired. Differential leveling runs for Department projects are to be done to a minimum accuracy of Second Order, Class II leveling, where μ is 0.026 feet or (0.008 meters), for Primary Control Surveys, and Third Order, where μ is 0.039 feet or (0.012 meters), for Mapping Control/Map Testing Surveys. A geodetic level and wooden or invar rod(s) or fiberglass bar coded rods as required for differential leveling and the rods must be not more than 12 feet (4 m) in length.
Accuracy classification from the “User Guidelines for Single Base Real Time GNSS Positioning” from the NGS, for real-time network GPS surveys is expressed as follows:
Table 3.2.4 NGS Real Time GPS Accuracy Class RT1 RT2 RT3 RT4 Accuracy (to 0.05 ft (0.015 m) H 0.08 ft (0.025 m) H 0.16 ft (0.050 m) H 0.50 (0.150 m) H base) 0.08 ft (0.025 m) V 0.13 ft (0.040 m) V 0.20 ft (0.060 m) V 0.82 ft (0.250 m) V Redundancy ≥ 2 observations ≥ 2 obs. N/A N/A 4 hrs differ 4 hrs differ Base Stations ≥ 2 in calibration ≥ 2 in calibration ≥ 1 ≥ 1 in calibration in calibration PDOP ≤ 2.0 ≤ 3.0 ≤ 4.0 ≤ 6.0 RMS ≤ 0.03 ft (≤ 0.010 m) ≤ 0.05 ft (≤ 0.015 m) ≤ 0.10 ft (≤ 0.030 m) ≤ 0.16 ft (≤ 0.050 m) Collection 1 sec 5 sec 1 sec 1 sec Interval for 3 min for 1 min for 15 sec for 10 sec Satellites ≥ 7 ≥ 6 ≥ 5 ≥ 5 Baseline ≤ 6 miles (≤ 10 km) ≤ 9 miles (≤ 15 km) ≤ 12 miles (≤ 20 km) Any Fixed Solution Distance
B.3-7
C. Datums. By state law, effective January 1, 1996, all Pennsylvania State Plane Coordinate System survey information will be computed in the North American Datum of 1983 (NAD83). By policy decision, effective January 1, 1996, all vertical survey information will be computed in the North American Vertical Datum of 1988 (NAVD 88).
Prior to January 1, 1996, the North American Datum of 1927 (NAD 27) and the National Geodetic Vertical Datum of 1929 (NGVD 29) had been used for project datums. NAD 27 and NGVD 29 may no longer be used for Department projects. Acceptable surveys will be balanced in accordance with Chapter 4 of "State Plane Coordinate System of 1983" by the National Geodetic Survey. From which NGS has compiled new standards and constants for each State as part of the newer horizontal control network which is referred to as the State Plane Coordinate System of 1983 (SPCS 83). Subsequent surveys using these control stations may require adjustment from grid azimuths and distances. Ground level distances must be derived by dividing the grid distance by the grid factor (product of scale factor and elevation factor). Ground level angles (and bearings) may be very close and acceptable for field use without further consideration. The decision to adjust grid azimuths for field use must be based on the significance of the adjustments with respect to the precision of the instrument.
On February 10, 2007, the National Geodetic Survey completed a national readjustment of all National Geodetic Reference System (NGRS) stations that had their positions determined exclusively by GPS observations. This new national readjustment provides a homogeneous network of all NGRS GPS observed stations (C.O.R.S., H.A.R.N., F.B.N., C.B.N., P.A.C.S., S.A.C.S., etc…) across the nation. The new datum adjustment tag is NAD83 (NSRS2007), better known as NAD83 (2007). As noted above, all Department control surveys will be based on NGRS stations. Thereby, all Department control surveys will be tied to and noted with the NAD83 (2007) datum adjustment tag.
3.3 GLOBAL POSITIONING SYSTEM
Global Positioning System (GPS) is a Department of Defense navigation system which uses an orbiting system of satellites carrying precise atomic clocks to determine position in real time, anywhere on earth, to an accuracy of 30 feet (10 m). By using two or more receivers collecting data from the same satellites simultaneously, and processing the data, it is possible to determine relative positions to sub-centimeter accuracy. There are two basic methods in GPS surveying: carrier phase and code. A. Carrier Phase Tracking. The most accurate GPS method is carrier phase tracking, which results in typical accuracies of 0.02 to 0.06 feet (0.005 m to 0.02 m) 1 to 3 parts per million (ppm) of the distance between stations. Carrier phase technique involves resolution of the phase of the carrier to about 0.006 feet (0.002 m). However, it is necessary to determine the integer number of wavelengths (integer bias) passed before signal acquisition and tracking began. A minimum of four (4) satellites are required to be tracked at fixed epoch intervals. Carrier phase can be further broken down into static and kinematic surveying. Static surveying is the most accurate, and involves the simultaneous occupation of the survey stations for a period of 45 minutes or more. Dual frequency techniques (using L1 and L2, B.3-8 rather than just L1) can shorten the required time to several (1 to 20) minutes over short to medium < 6 miles (< 10 km) length lines. This is known as fast or rapid static. Shorter observation times can be affected by multipath, which the error introduced by the radio wave is being reflected by a nearby surface and introducing added length into the distance from the satellite. Because of this, it is important to select open sites when using fast ambiguity resolution techniques. Negative effects of multipath tend to cancel out as the length of the observing session increases. Kinematic surveying yields centimeter accuracy once the integer biases are resolved. As long as lock is maintained on the satellite signals (4 or more), the receiver can be moved and, once stationary, can resolve the baseline in seconds rather than minutes or hours necessary in static surveying. Real time kinematic surveying is possible using a radio link between the receiver at a known point (base) and a roving receiver. Data from the base and rover is combined and processed on board the roving receiver to yield centimeter accuracy.
B. Code Tracking. The other GPS method being used is known as code. This uses broadcast data from the satellite to determine autonomous positions. Theoretical autonomous accuracy is about 30 feet (10 m). By using two receivers, one on a known survey station, it is possible to correct the observations to attain an accuracy of better than 3 feet (1 m).
C. GPS Techniques. When the Global Positioning System (GPS) is used, the specifications outlined in Table 3.2.1 above must be adhered to.
D. Redundancy. Redundancy can provide proof of the precision to which a measurement is made. In order for this proof to be valid, the inclusion of possible error sources must not be systematically duplicated in the repeat measurements. Redundancy in a GPS survey is achieved primarily by way of a change in the relative geometry of the satellite constellation. For GPS surveys, the geometry of the satellite constellation must be different for repeat station occupations in order to eliminate potential sources for systematic errors due to multipath, orbital bias, and unmodeled ionospheric and tropospheric delay. Even if the repeat observation is made on another day, data must be collected at a different sidereal time (generally, a four (4) hour schedule time difference between observations) in order to obtain a different satellite configuration. Redundant observations also provide the additional verification of centering errors and a second set of antenna height measurements.
E. Specifications. When a station is to be occupied more than once in consecutive sessions, the tripod should be reset between occupations. At least 20% of the stations should be occupied three or more times. At least 5% of the total number of independent baselines should be measured twice. It is acceptable to use the broadcast ephemeris for the Mapping Control/Map Testing Survey, although the precise ephemeris is recommended. The precise ephemeris is required for the Primary Control Network. If a fixed height tripod is used, the nominal height and the manufacturers name and model number should be recorded. If a variable height tripod is used, the height must be measured in meters with separate measuring scales at both the start and the end of each observing session and recorded. Tribrachs and other centering devices should be checked on a weekly basis, and a log kept of the results. A log sheet must be prepared for each occupation, and must include as a minimum the following B.3-9
data: name of operator, antenna and instrument serial and model numbers, centering device identifier, height of instrument, start and stop times, station name, project name, description, sketch (sketch not necessary for consecutive occupations), and a description of any problems or unusual occurrences during the observation.
F. Network Design. The network should be designed to enable loop closure analyses to be performed on all stations. A loop is defined as a series of independent baselines (measured at different times) which form a geometrically closed polygon. The maximum permissible misclosure in terms of loop length is 12.5 ppm.
G. Least Squares Adjustments. A minimally constrained and a fully constrained adjustment of the GPS network will be analyzed and supplied. Geoid heights from the latest geoid model available from the National Geodetic Survey must be included. The adjustment must only use independent (non-trivial) vectors. The following statistics must be evaluated for each adjustment: Network variance of unit weight (variance factor) and degrees of freedom. A variance factor of less than 1.5 and approaching 1.0 is considered a conservative statistic for geodetic control surveying. Posteriori errors must be computed at the 95% (two-sigma) confidence level for the adjusted station coordinates and for relative positions for all station combinations. Any significant changes between statistics from minimally constrained adjustment and fully constrained adjustment must be investigated.
3.4 TRAVERSE METHODOLOGY
The traverse will begin and end on stations of at least the same accuracy classification or higher. These control stations will be stations of the National Geodetic Reference System (NGRS) or have been derived from and adjusted to NGRS stations. A starting and ending azimuth for each traverse must be provided. In addition, an azimuth check will be performed along the traverse at intervals not to exceed more than 25 stations, and at a maximum interval between observations of approximately 4 miles (6 kilometers). Accuracy classifications from the “Standards and Specifications for Geodetic Control Networks” from the FGCC, must be adhered to.
A. Angles and Azimuths. Traverse angles will be observed using a theodolite with standard deviation of a direction (direct and reversed) of 2 seconds. When running the traverse, forepoint stations (backsight and foresight) must be occupied with a tripod and target. Sights by plumb bob or range pole/prism pole are not acceptable. The method of forced centering should be used. A reconnaissance of the traverse route should be performed prior to observations of angles and distances. Any intersection stations (antennas, distant church spires, water tanks, etc.) which are visible from two or more stations of the traverse should be included in the scheme. All stations of the traverse should be marked by a rebar and cap if in open ground, or by a PK nail or railroad spike if in pavement. Starting and ending azimuths B.3-10 on the traverse will consist of an intervisible control station or an azimuth mark (at least 1320 feet (400 m) distant). Nearby (less than 1320 feet (400 m) away) reference marks cannot be used for azimuth control, and intersection stations of NGRS should be used with extreme caution due to problems of identification, accuracy, and movement. If it is necessary to establish a new azimuth mark, astronomical methods (Polaris at any hour angle) may be used. Due to latitudes in Pennsylvania (40-43), extreme care must be taken in leveling the instrument. If an automatic compensator is available, using an optical theodolite, the following procedure should be used for initial leveling: Level the instrument using the plate level. With the telescope in any position, tighten the vertical clamp and read the vertical circle. Turn the instrument through 180 (do not disturb the vertical angle setting) and read the vertical circle. Compute the mean of the two readings. Set this on the micrometer. Turn the telescope until it is parallel to two footscrews. Turn the two footscrews carefully in opposite directions until the micrometer lines are coincident. Turn the telescope 90 and move the third footscrew to bring the micrometer lines into coincidence. Repeat the procedure until the vertical circle reading remains constant. During the observations, the leveling should be checked and recorded before the first position, and after every other position, as follows: Turn 90 left of the star, clamp the vertical circle, read, and record the vertical angle. Turn 90 right of the star, clamp the vertical circle, read, and record the vertical angle. Do not re-level the instrument during the observation sequence. If an electronic theodolite with dual axis compensation is used, it is not necessary to perform these steps, as long as the compensation is activated. The observation sequence is as follows: (1) Point on backsight. Record circle reading. (2) Point on star, record Coordinated Universal Time (UTC) and circle reading. (3) Reverse the telescope, repeat step 2. (4) Repeat step 1.
This constitutes one position.
Data should be reduced using software, which is capable of a computational accuracy of 0.5 seconds of arc or better. Each position should be computed separately. The mean azimuth of n positions is computed as follows:
( X i ) X n = n Any observation which deviates by more than 5 seconds from the mean should be rejected, B.3-11 and that position should be reobserved. Astronomical azimuth should be converted to a geodetic azimuth by applying the Laplace correction (available from DEFLEC99, an interpolation program from the National Geodetic Survey) and then to a grid azimuth using the grid convergence at the station. All azimuths should be referenced to Pennsylvania State Plane Coordinate System grid north (north or south zone, as appropriate).
B. EDM Distances. Traverse distances will be observed using an electro-optical EDM with a base error of 0.02 feet (5 mm) or better, and a proportional error of 5 ppm or better 0.02 feet (5 mm + 5 ppm). The EDM should be checked every 6 months and/or at the beginning of a long duration project. This checking can be done on one of the several calibration baselines established across the state by the National Geodetic Survey. Checking procedures are outlined in the document "Use of Calibration Base Lines", NOAA Technical Memorandum NOS NGS-10, available from the National Geodetic Survey.
An EDM distance will be measured to all ground stations. Height of instrument and height of targets will be recorded. Any vertical offset between the theodolite and the EDM and between the target and the prism will be recorded at each setup. Temperature will be recorded to the nearest degree Fahrenheit or Celsius, and the pressure to the nearest millibar or inches Hg. If atmospheric correction is entered into the instrument (either T and P or actual ppm correction from a nomogram), it must be clearly indicated in the notes. All distances (slope) and zenith angles must be measured both ahead and back between traverse stations. If manual recording of the data is being performed, the distance should be recorded. Time and date must also be indicated on each page. Distances may be automatically adjusted to their corresponding field values directly within the EDM instrument. However, for manual adjustments, distances must be reduced to the grid before using in computations. This is a two or three step process, depending on whether the atmospheric corrections were entered into the instrument. Slope EDM distance is first corrected for atmospheric delay, if necessary, and then reduced from slope to a horizontal measurement, using the observed zenith distances. If the atmospheric correction is needed, it is important to use the proper table or formula for the instrument being used, as it differs among different models. The next reduction is to the ellipsoid. For the purposes of distance reductions in Pennsylvania, the ellipsoid elevation is equal to the approximate height above "sea level" minus 108 feet (33 m) for the GRS 1980 ellipsoid (used on NAD 83). Ellipsoid and geoid can be considered coincident when using the NAD 27. The formula for reduction to the ellipsoid is as follows:
Dh * 6375000 De = 6375000 + h where Dh is horizontal distance, and h is elevation of ground above sea level (computed as the mean geoid height, N, plus the mean elevation, H). Finally, the ellipsoid distance is multiplied by the scale factor to obtain a grid distance. On long lines, mean of the scale factor at the endpoints should be used. If a geodetic azimuth is being used, it must be corrected by the convergence to obtain a grid azimuth. Angular misclosure must first be checked, and must be less than 4.5" √N for Second Order, Class II and 10" √N for Third Order, Class I where N is the number of stations for carrying the azimuth. Raw traverse closure should be B.3-12
checked after adjustment of the angular misclosure. Traverse(s) should be adjusted using a least squares adjustment.
C. Eccentric Observations. When it is not possible to directly occupy a photogrammetric panel or photo identity with GPS, an eccentric occupation must be established with a reduction to center. An azimuth mark companion station must be set and, two sets of directions, one of the station angle and one of the explement angle, must be measured. Slope distance and zenith distances must be measured ahead and back if the photogrammetric station is occupiable with a tripod. If a non-occupiable station is used (i.e. pole), the distance must be measured with an EDM in feet (meters) and checked with a tape in feet (meters).
3.5 PRIMARY CONTROL NETWORKS
Primary Control Networks (PCN) consist of permanent stations marked by Pennsylvania Department of Transportation bronze disks set in concrete, grouted in outcropping bedrock or other massive or permanent structures, or similar existing monuments of other agencies. Exceptions to the monumentation standard must be approved by the “Photogrammetry & Surveys Section.” The minimum requirements for concrete monuments are 3.0 feet (1 m) deep by 0.70 feet (0.20 m) at the top and belled toward the bottom to a diameter of 1.5 feet (0.50 m). A steel reinforcing rod 2.0 feet (0.60 m) long must be placed inside the monument. A properly stamped PennDOT bronze disk will be placed on top of the concrete with the two tongues on the back of the disk slightly widened refer to Figure 3.5.1 “Schematic of the Standard PennDOT Concrete Monument.” Photogrammetry & Surveys Section is to be notified within three days prior to setting permanent monuments. PA ONE CALL is to be contacted to assure underground utilities will not be damaged. The required spacing of the primary control is at 2 miles (3 km) intervals. Each monument set will have a minimum of one azimuth mark, set at a minimum distance of 1320 ft (400 m) from the primary control monument. The azimuth mark will be the adjacent inter-visible primary control station. A completed Department “Record of Control Sheet - Horizontal” (see Appendix C-3) in digital format, as approved by the Photogrammetry & Surveys Section, must be prepared for each station. The horizontal record of control sheets will be archived by the Photogrammetry & Surveys Section in the www.penndotpams.org website for future retrieval and use by PennDOT and the general public. The District Survey Manager will define nomenclature for station names.
The minimum acceptable accuracy for the Primary Control Network, from the “Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques” from the FGCC, is Group C, First Order, 10 ppm when using the Global Positioning System. External horizontal control (NGRS) must be brought in to the stations of the Primary Control Network.
If GPS elevations are required (acceptable for mapping scales of 1” = 100’ (1:1000) or smaller) a minimum of four Second Order or higher NGRS, or Third Order PennDOT vertical control stations will be occupied, distributed in at least three quadrants around the center of the project. If a sufficient number of NGRS benchmarks are not available, and with the approval of the “Photogrammetry and Surveys Section,” Third Order marks of other agencies B.3-13 may be used. If other marks are used, a Third Order level line should be run through the long dimension of the project, passing through as many monuments as possible.
Figure 3.5.1
The vertical component of the PCN for 1”= 50’ (1:500) or larger scale mapping will be determined by differential leveling techniques. Benchmarks are required at 0.5-miles (0.75 km) intervals for a mapping scale of 1”= 50’ (1:500) or larger and their horizontal position (Latitude / Longitude) must at least be derived from scaling a USGS Quadrangle map or by hand-held GPS. A completed Department “Record of Control Sheet - Vertical” (see Appendix C-4) in digital format, as approved by the Photogrammetry & Survey Section, must be prepared for each benchmark. Benchmark nomenclature will consist of the party chief’s three letter initials and followed by a three digit number that starts at 001 and increases with each new benchmark to be set. The numbering sequence will increase, over time, regardless of project (example: CIH 001, CIH 002, etc.). The vertical record of control sheets will be archived by the Photogrammetry & Surveys Section in the www.penndotpams.org website for future retrieval and use by PennDOT and the general public.
Differential leveling runs for Department projects are to be done to a minimum accuracy from the "Standards and Specifications for Geodetic Control Networks" by the FGCC, Second Order, Class II for Primary Control Networks. A geodetic level and wooden or B.3-14
invar rod(s), or fiberglass bar coded rods, or calibrated fiberglass rods are required for differential leveling and the rods must be not more than 12 feet (4 m) in length. Benchmarks are to be placed on permanent structures (i.e. bridge abutments, inlet headwalls, traffic signal bases) or constructed as permanent concrete monuments as outlined above.
3.6 MAPPING CONTROL/MAP TESTING SURVEYS
Mapping Control Surveys (MCS) consist of targeted points and photo identities necessary for the analytical aero-triangulation process and Map Testing Surveys (MTS) consist of photo identifiable mapping features necessary for map testing purposes. Mapping control and map testing stations are marked by a semi-permanent type of monumentation, i.e. rebar and cap, railroad spike, chiseled "X", 100-penny nail, PK nail, etc. The MCS/MTS should be based on the Primary Control Network or NGRS stations, which control the Primary Control Network. The proposed Primary Control network must be approved by the “Photogrammetry & Survey Section.” MCS/MTS points must be marked on the project aerial photography with the station name and description. MTS points are only photo identifiable map features (sidewalk corners, manholes, etc…) that are evenly distributed (approximately every 3 stereo- models and / or at the discretion of the Department) within the mapping limits of the project. The “Photogrammetry & Survey Section” will define nomenclature for MCS/MTS station names.
The minimum acceptable accuracy for MCS/MTS is the "Standards and Specifications for Geodetic Control Networks" by the FGCC, Third Order, Class I, 100 ppm when using conventional traversing techniques the “Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques” by the FGCC, Group C, Second Order, Class I, 20 ppm when using the Global Positioning System and the “User Guidelines for Single Base Real Time GNSS Positioning” by the NGS, Class RT2 when using real-time GNSS positioning.
GPS methods for MCS/MTS can include, but are not limited to the following: static, kinematic, pseudo-static, and fast ambiguity, also known as rapid static or fast static. Accuracy standard required for MCS/MTS using GPS is Group C, Second Order, Class I (20 mm + 20 ppm) and Class RT2 when using real-time GNSS positioning. Observations for the MCS/MTS should be of sufficient duration to ensure meeting the required accuracy. At least two NGRS stations or stations from the Primary Control Network must be used to establish the MCS/MTS, distributed uniformly throughout the project. Duration of any GPS observation session is greatly variable, depending upon, among other things, the desired level of accuracy, satellite geometry, the observable recorded, the observation techniques, and the processing software. Adequate results have been obtained using occupation times ranging from less than a minute up to several hours. Because of constantly changing technology, it is not feasible to restrict the length of observations or method used based on current technology. Manufacturer's recommendations should be followed for each type of survey. Specifications for Group C surveys outlined in "Geometric Geodetic Accuracy Standards and Specifications B.3-15 for Using GPS Relative Positioning Techniques", by the FGCC, and the “User Guidelines for Single Base Real Time GNSS Positioning”, by the NGS should be adhered to, with the following exceptions: A minimum of two receivers must be used simultaneously, using carrier phase tracking. High Production GPS techniques such as rapid static and kinematic procedures may be used. The minimum observation time will be as needed to obtain the required accuracy. For observation sessions lasting less than 20 minutes, at least 5 satellites should be tracked at both stations for 75% of the observation session. For radial GPS techniques, at least 75% of the stations in the network should be occupied two or more times, preferably utilizing different base stations.
A. Horizontal. If conventional methods are used, the specifications outlined in "Standards and Specifications for Geodetic Control Networks,” by the FGCS, should be adhered to with the following exceptions: Angular observations consist of four positions with a 1-second instrument, rejection limit 5 seconds. Astronomical observations consist of four acceptable observations on Polaris at any hour angle, rejection limit 7 seconds.
B. Vertical. The vertical component of the MCS / MTS for mapping at a contour interval of 1.0 foot (0.25 m) or greater may be determined by the same procedures as the horizontal component, i.e. GPS derived orthometric heights. Benchmarks are not required on projects that use only GPS vertical control (i.e. projects that have 1” = 100’ (1:1000) or smaller mapping scales). Benchmarks are required at 0.5 miles (0.75 km) intervals (as described previously) for a mapping scale of 1”= 50’ (1:500) or larger throughout the project. For the Mapping Control and Map Testing Stations, an accuracy of 0.1 feet (0.03 m) will be required using GPS and differential leveling methods. If this accuracy is not obtainable, then Third Order differential leveling (as described below in this section) will be required. GPS Derived Orthometric Heights. When GPS vertical control is being performed, the latest geoid model from NGS, such as GEOID09, must be incorporated into the adjustment as a comparison tool. No heights determined from the geoid model are to be held fixed in the final adjustment. In addition, vertical control stations must be located in at least three quadrants from the center of the project, and they must be located near or outside the perimeter of the project. The vertical control stations can be any mapping control, map testing or primary control station that have been differentially leveled to or an existing benchmark as described above – all of which must be occupied using GPS during the MCS/MTS. It may be necessary (at the discretion of the “Photogrammetry & Survey Section”) to run a differential level line(s) through the project to strengthen the vertical component if existing control is a weak configuration. A minimum of three (3) well-spaced vertical stations, as described under the section: GPS B.3-16
Derived Orthometric Heights, above, must be included along with a detailed geoid model such as GEOID09, from NGS. Accuracy of the GPS derived orthometric heights must be 0.10 feet (0.03 m) or better. Trigonometric Levels. Trigonometric levels are acceptable for 1” = 200’ (1:2000) scale mapping or smaller. The following requirements apply: (1) Maximum sight distance for trigonometric leveling is 1500 feet (500 m). (2) Zenith distance and EDM distance (or, alternatively, the delta elevation as determined by the total station) should be measured in both directions. (3) Care must be taken to ensure the line of sight does not pass too close to the ground, or to other heat radiating surfaces. (4) Forward and backward trigonometric height differences can be compared by computing the curvature and refraction correction.
2 2 Cf = 0.667M = 0.0239F or 2 (Cm = 0.0785K ) where C f in feet or C m in meters, M is distance in miles, F is distance in thousands of feet, and K is distance in kilometers.
2 2 R f = 0.093M = 0.0033F or 2 (Rm = 0.011K ) where R f in feet or R m in meters, M is distance in miles, F is distance in thousands of feet, and K is distance in kilometers.
Most total stations have the capability to internally correct height difference for curvature and refraction, so care must be taken when recording and computing trigonometric heights. When observing reciprocal (near simultaneous) trigonometric levels, the curvature, and refraction terms cancel. Height difference can be computed as:
12* sin 12+ 21* sin 21 1 - 2+ 1 - 2 H = D D + HI HT HT HI 2 2 where D12 and D21 refer to the slope distance forward and back, α12 and α21 refer to the vertical angle forward and back, and HI1, HI2, HT1, and HT2 refer to the heights of instruments and targets at each station.
For trigonometric elevations, zenith distances and EDM distances must be measured both forward and backward on each line and the overall elevation closure must meet Third Order closure specifications.
B.3-17
Differential Leveling. The vertical component of the MCS/MTS for 1” = 50’ (1:500) scale mapping or larger may also be determined by Third Order differential leveling methods. Procedures are outlined in "Standards and Specifications for Geodetic Control Networks", by the FGCC, for Third Order leveling should be adhered to, with a geodetic level and wooden or invar rod(s) or fiberglass bar coded rods as required for differential leveling and the rods must be not more than 12 feet (4 m) in length. Differential leveling will be required on all MCS/MTS stations for 1” = 20’ (1:200) scale mapping or larger.
Completed mapping control survey data and reports (PCN, GPS, and conventional, horizontal and vertical) must be approved by the “Photogrammetry & Survey Section” prior to use in analytical aero-triangulation and/or photogrammetric mapping.
C. Airborne GPS. Airborne GPS (AGPS) can be used to supplement and reduce the number of mapping control stations necessary for the analytical aero-triangulation process. Airborne GPS is accomplished by collecting kinematic GPS data in the aircraft and static GPS data on or with a NGRS/PCN station simultaneously. The vector from the airplane GPS antenna to the aerial camera photo center must also be known. The GPS data is post- processed to determine aerial photo center coordinates.
When GPS-derived orthometric heights are determined for the AGPS vertical control, the latest geoid model from NGS, such as GEOID09, must be incorporated and used for the adjustment.
Only one vertical control station needs to be determined (as outlined above for PCN and/or MCS/MTS) and held fixed in the adjustment.
Coordinates derived from Airborne GPS are acceptable enough to be used for 1” = 100’ (1:1000) scale mapping or smaller and for various planimetric-only mapping purposes on 1” = 50’ (1:500) scale mapping or smaller.
Relative accuracies of AGPS coordinates are to meet the same accuracies as the MCS/MTS mentioned above. If this accuracy is not obtainable, then more mapping control stations are required to adequately supplement the analytical aero-triangulation process.
3.7 DELIVERABLES
Following is a list of the deliverables for the survey network, when GPS is used and if conventional traverse and/or differential leveling methods are used in addition to GPS. Submit one copy of the following on CD in the formats listed below. Report of survey, which includes the following items: (1) Narrative description of the project, which summarizes the project, conditions, objectives, methodologies, and conclusions. (2) Discussion of the survey control used, observation plan, equipment used, satellite constellation status, and observable recorded. B.3-18
(3) Description of data processing performed. Note software used, version number, techniques employed including integer bias resolution, if applicable, and error modeling. (4) Provide a summary and detailed analysis of the minimally-constrained and fully- constrained least squares adjustments performed. List observations and parameters that are included in the adjustment. List absolute and standardized residuals, variance of unit weight, and relative confidence for the coordinate differences at the 95% confidence level. (5) Identify any data or solutions excluded from the network with an explanation as to why it was rejected. (6) Department “Record of Control Sheets – (Horizontal and Vertical)” (see Appendix C- 3, C-4) will be provided in Microsoft Word for each permanent horizontal and vertical control station. An electronic format of this document is available through the Department’s Photogrammetry & Surveys Section. (7) Raw data files (8) Original field books and copies of observation logs/notes. (9) Digital pictures of all observed survey stations. (10) Include a diagram (site map) of the project stations and control at an appropriate scale. (11) Any other required CD deliverables as noted below.
Required Deliverables: Two (2) hard copies of the overall site map. One (1) digital CD for the entire survey report, that will contain the following directory file structure listed below. All supporting data will be placed in the appropriate file directory on the CD: 01 Narrative 02 Existing Record of Control Sheets 03 Project Coordinates 04 New Record of Control Sheets 05 Baseline Results 06 Loop Closures 07 Minimally-Constrained Adjustment 08 Constrained Adjustment 09 GPS Data 10 Differential Levels 11 Field Notes 12 Control Diagram
All digital data is to be in the following formats: B.3-19
01 Narrative - Microsoft Word (*.doc) or Microsoft Excel (*.xls) or Adobe (*.pdf) 02 Existing Record of Control Sheets - Microsoft Word (*.doc) or Adobe (*.pdf), or Web-based (*.html) 03 Project Coordinates - Microsoft Word (*.doc) or Microsoft Excel (*.xls) - Project coordinates are to be given in US Survey Feet and Metric 04 New Record of Control Sheets - Microsoft Word (*.doc) - Horizontal and Vertical Record of Control Sheets are to be in the “Photogrammetry & Surveys Section” approved format (see Appendix C-3 & C- 4). 05 Baseline Results - Microsoft Word (*.doc) or Adobe (*.pdf) or Web-based (*.html) 06 Loop Closures - Microsoft Word (*.doc) or Adobe (*.pdf) or Web-based (*.html) 07 Minimally-Constrained Adjustment - Microsoft Word (*.doc) or Adobe (*.pdf), or Web-based (*.html) 08 Constrained Adjustment - Microsoft Word (*.doc) or Adobe (*.pdf) or Web-based (*.html) 09 GPS Data - Trimble (*.dat, *.ssf, *.sst) and/or RINEX 10 Differential Levels - Microsoft Word (*.doc) or scanned Adobe (*.pdf) 11 Field Notes - Microsoft Word (*.doc) or scanned Adobe (*.pdf) or digital picture (*.jpg) 12 Control Diagram - Adobe (*.pdf) or Delorme X-Map (*.dmt) B.4-1
CHAPTER 4
ANALYTICAL AERO-TRIANGULATION
4.0 INTRODUCTION
The analytical aero-triangulation process is used to reduce the number of field surveyed Mapping Control Points (MCP) needed for stereo compilation of photogrammetric mapping. This chapter deals with procedures and requirements for performing analytical aero-triangulation for highway projects. The final analytical aero-triangulation solution must be approved by the Photogrammetry & Surveys Section prior to production of photogrammetric mapping of the project.
4.1 ANALYTICAL AERO-TRIANGULATION
Analytical aero-triangulation provides coordinates to supplement MCP networks. MCP and benchmarks are appropriately placed throughout the project. In each stereoscopic model, analytical aero-triangulation is used to produce ground (X, Y, and Z) coordinates to supplement MCP. These supplemental points will be used for precision orientation of the stereo model for map compilation of the highway project. Points produced by analytical aero-triangulation may not be used in lieu of required MCP as discussed in Part B, Chapter 3, Section 3.6.
A. Measuring for Analytical Aero-Triangulation. Precision of the photogrammetric equipment and software contributes to the overall accuracy of the analytic aero- triangulation. These measurements will be used to locate X, Y, and Z coordinates of photographic reference fiducial marks and MCP, photographic images, and aero- triangulated points. Accuracies achieved must satisfy established X, Y, and Z coordinate tolerance levels for each point identified. Softcopy processes are required. Digital scans produced directly from the original aerial film will be used. Scans of 7.5 to 15 microns are required for the production of large scale final design photogrammetric mapping.
B. Accuracy. As determined by analytical aero-triangulation, the horizontal position (X and Y) and elevation (Z) coordinates of all MCP targeted on the ground before photography must meet requirements established in Table 4.1.1. Tolerances listed in Table 4.1.1 are expressed as a fraction of the average aircraft flight height above mean terrain for the project.
B.4-2
Table 4.1.1 Error Tolerances for Analytical Aero-triangulation Absolute Error as a Fraction of Flight Height
ERROR HORIZONTAL POSITION ELEVATION TOLERANCE CLASSIFICA X Y Z TION 3x 3x 3x Maximum ( ) RMSE RMSE RMSE Root Mean Square 1 1:12,000 1:12,000 1:10,000
1 RMSE - expression for accuracy of a single observation; defined as the square root of the quantity: Sum of the squares of the errors divided by the number of errors. All three accuracy requirements, maximum, average, and root mean square must be fully met.
C. Supplemental Control. Soft Copy: Supplemental control points (pass points) may be measured manually or by automatic correlation. Identifiable points are not necessary, but careful QA/QC must be done to ensure that points are well distributed and measured in at least three photographs. For automatic correlation, care must also be taken to ensure that measurements are parallax free.
D. Interval of Supplemental Control Spacing on Aerial Photography. A minimum of six horizontal/vertical control points will be selected for each stereoscopic model required in subsequent measuring and mapping operations. Each control point will be on or near a line that passes through or near the principal point and is perpendicular to the flight line. The control points will be located in positions on the photograph in order to provide a strong geometric configuration for leveling the stereo model and to fully encompass the area to be mapped.
E. Measurement Corrections. In computing X, Y, and Z coordinates, correction will be made for aerial camera lens distortions, deformation of photographic film, and atmospheric refraction.
F. Photography Strip Ties. Wherever separate strips of photographs side lap or cross, they must be tied together by analytical aero-triangulation for accomplishing the subsequently required measuring and mapping. For this purpose, ground points will be selected which provide appropriate stereoscopically corresponding images on the adjacent side lapping, or crossing, strip or strips of photographs. Wherever possible, targeted points and other ground identifiable image points will be selected for determining supplemental control in line of flight. Otherwise, additional and suitable image points will be selected stereoscopically to adequately tie the strips together. A minimum of one tie point per model will be required. B.4-3
G. Point Labeling. An identifying number will be assigned to each photographic image point for which the X, Y, and Z coordinates are computed. Each number will be related to the photograph on which the point appears, and will serve to classify the point as to whether it is applicable to horizontal and/or vertical control. Points will be circled and their number placed on the control annotated set of contact prints.
For automatic correlation and soft copy manual point measurement, point naming as assigned by the software is acceptable.
H. Software and Process. Analytic aero-triangulation software to be used in the procedure must be capable of executing a simultaneous adjustment (Bundle) on all strips and photographs necessary to cover the work area. It must be capable of solving for a minimum of 48 strips or 500 photographs in one pass. If the project involves more than 48 strips or 500 photographs, then the solution may be split, but distribution of horizontal and vertical control points must be appropriately designated as to support two or more computations.
When it is necessary to split the computation into two or more sectors, there must be sufficient coverage overlap between the sectors. For example, if there are 10 strips covering the area to be mapped, then the first solution should include strips one through six, the second solution should include strips four through ten. Tie points between strips four and five should be held as control points to insure a proper tie between solutions. If stereo compilation must be started as soon as possible, then only strips one through four should be released for that purpose.
Analytical aero-triangulation software should offer opportunities for isolation of blunders, error detection and diagnosis, and analysis of results in progressive computational steps. If horizontal and/or vertical control points have been obtained in sufficient numbers (as to exceed distribution, location, and frequency recommended in Chapter 3 - Targeting and Control Surveys), then isolated points may be removed from the control point data file. These isolated points would otherwise have provided for a solution that exceeds misclosure requirements, thereby degrading quality and accuracy of the general solution. In such an event, discarded points will be noted and a description of the problem and magnitude of misclosure will be made for the record and future reference.
I. Reports and Records. After analytic aero-triangulation procedures have been completed, a report will be prepared consisting of a brief summary of results, computations, accuracies, list of control points not used in the solution, reasons for their removal, and all other pertinent information. It will also include a printout of final analytic pass, from original field surveyed control point list, through all major computational steps, to final analytically generated control point value list. Aero-triangulation set up files will be part of the final deliverables and are to be placed on a separate disc or emailed. B.5-1
CHAPTER 5
DIGITAL MAP COMPILATION
5.0 INTRODUCTION
This chapter outlines digital mapping compilation procedures and requirements for aerial photogrammetric mapping projects. Formatting requirements and compilation procedures for digital map files are discussed. Section 5.2 - Map Contents deals with the presentation requirements for aerial photogrammetric mapping projects. This chapter promotes uniformity in the preparation of digital files by establishing the general format and presenting detailed information required for all photogrammetric mapping projects. Detail requirements for digital map editing and plotting are discussed throughout this chapter. In addition, index map development procedures and presentation requirements are outlined. The chapter concludes with a discussion on symbols, line weights, and lettering sizes to be used with digital maps. Additional consideration is given to the presentation of contour lines.
5.1 COMPILATION
Stereo photogrammetric methods used to compile maps will be in accordance with Department requirements. Precision analog/analytic photogrammetric instruments or photogrammetric softcopy workstations will be utilized.
Topographic maps will be compiled directly into or translated to MicroStation design file format. All data will be in three dimensional (3D) files. All topographic data (breaklines, mass points, spot elevations) will have their level displays turned off and settings saved prior to delivery. All topography will be collected utilizing Digital Terrain Model (DTM) methods see Section 5.2 D. Digital Terrain Models and Topography.
Any project less than 20 models may be delivered in one (1) MicroStation Design file. Any project over 20 models should be delivered in sheets that are cut to include approximately 10 models. (Example: 50 scale sheets would be approximately 4000’ X 4000’) Actual sheet size and orientation are left to the Photogrammetrist’s discretion.
A triangulated Digital Terrain Model will also be delivered in InRoads format.
PennDOT will require digital mapping to be delivered in the following format on CD or DVD media. 3D MicroStation files (format prior to Version 8) Digital terrain model (surface file) in TTN format Index file as specified in Pub. 122M Orthophoto images if required Text file containing observed map test coordinates B.5-2
PennDOT expects to begin using MicroStation V8 in the summer of 2004. Deliverables will then be in Version 8 format and some changes to level symbology can be expected.
A. CADD File Creation. The files shall be compiled utilizing the following working units:
English Metric Master Units = 1 sf 1 m Sub Units = 1 su 1 mm Sub Units per Master Unit = 1000 1000 Positional Units per Sub Unit = 1 8
ENGLISH METRIC 3D files: GO= 0, 0, 2147483.65 3D files: GO= -370,000, -30,000, 268,435.4560 2D files: GO= 0, 0 2D files: GO= -370,000, -30,000
All data will conform to level, color, and line weight assignments set by the Department. All files will be compatible with MicroStation software.
The naming convention for CADD map files is as follows:
FORMAT: ccssssxx.dgn cc = County Number, two digits ssss = State Route Number, four digits xx = Last two digits of lower exposure number that makes up the stereo model .pln = Planimetric file identification extension .dtm = Digital terrain model file identification extension
B. Image Scanning. Original processed 9”x 9” aerial film will be scanned directly on to an aerial film scanner. Scans will be available from the Department unless specified otherwise.
5.2 MAP CONTENTS
A. Matches. The area between adjacent models will be thoroughly checked to assure continuity of planimetric and topographic detail. Work should end at the photo center except in the case where partial models exist, where flight lines tie together, or on the end file of a project.
B. Control Stations. All monumented horizontal and vertical control points used or established in the Mapping Control Survey (MCS), and test targets will be included in the digital files. All such control points will be precisely located, properly symbolized, and accurately identified.
B.5-3
C. Planimetry. As visible on and identifiable from the aerial photography, the following natural and man-made features will be shown on the mapping at a direct compilation scale of 1”= 200’ (1:2000) and 1”= 100’ (1:1000):
Airports & Runways Golf Courses-Fairways, Railroads (Centerline) Aqueducts Tees, Greens, Sandtraps Reservoirs Athletic Fields: Greenhouses Retaining Walls (Prominent) Tennis, Basketball, etc. Lakes & Ponds Rivers & Streams Borrow Pits & Quarries Orchards & Nurseries Roads Bridges Parking Areas (Prominent) Ruins Buildings Parks (Over 1 acre (0.4 HA)) Sewage Treatment Canals Piers & Wharfs Plant Outlines Cemeteries Piles (coal, sand, large) Smokestacks (Prominent) Culverts Pipelines (x-country) Swamps Dams Pools (over 50’(15 m) long) Tanks Ditches (Prominent Only) Power Generating Stations Trestles & Sub-stations Tunnels, Portal Driveways (Over 200’(60 m)) Power Lines & Towers Walls (Prominent) Fences(Prominent) Radio Towers Wooded Area Outlines Falls
Mapping at this scale will not include relatively smaller features (e.g. such as catch basins, hydrants, manholes, sidewalks, single trees and bushes, roadside poles, minor property fences, walls or hedges, street signposts, route markers). Prominent boulders 0.02’ (5 mm) or larger at final map scale will be shown and labeled.
As visible on and identifiable from the aerial photography, the following natural and/or man-made features will be shown on mapping at the compilation scale of 1”= 50’ (1:500):
Airports & Runways Greenhouses Rivers & Streams Athletic Fields: Guiderail & Posts Roads Tennis, Basketball, etc. Hedges Rock Outcrops Billboards Lamp Posts (Private) Ruins Boulders Light Poles Shoulders-roads Bridges Manholes Shrubs Buildings Monuments Sidewalks Bushes Nurseries (Plantings) Silos Catch basins Orchards Signs Cemeteries Parking Areas Stacks-Chimneys Conveyors Parks & Playgrounds Step Culverts Patios Support Poles Curbs Piers & Wharfs Swamps Dams Piles (coal, sand, etc.) Tanks Ditches Pipelines Trails Driveways Platforms & Ramps Traffic Lights Falls Pools (Swimming) Trees B.5-4
Fence Power Lines & Towers Tunnels Fire Hydrants Quarries & Borrow Pits Utility Poles Field Roads Radio Towers Walls Flagpoles Railroads (both rails) Wells Fords Rapids Wooded Area Fuel Pumps Retaining Walls Golf Courses: Fairways, Tees, Greens, Sandtraps
Buildings and similar dimensional objects will be correctly outlined and oriented, and will be to scale, except that building dimensions smaller than 0.01’ (2.5 mm) at map scale will be symbolized 0.01’ (2.5 mm) in size. Minor irregularities in building outlines smaller than 0.005’ (1.25 mm) at map scale may be ignored. Portions of fully developed urbanized areas, when designated by the Department may be hatched. Prominent boulders 0.01’ (2.5 mm) or larger at final map scale will be shown and labeled.
All political subdivision boundary lines will be shown as accurately as possible on the maps. US Geological Survey (USGS) 7 1/2-minute quad maps will be used to ascertain the existence and approximate location of these lines. The notation "Approximate Location" will be shown on boundary lines.
D. Digital Terrain Models and Topography. Maps will contain all topographic features visible or identifiable on the aerial photography. All topographic data will be compiled using DTM (digital terrain model) methods. Breaklines indicating where the slope of terrain changes will be digitized directly into the digital files, along with mass points to properly define the surface to be mapped. Mass points (random points) will be collected on a grid of 1/10 the photo scale in areas between breaklines. DTM data will not be generated from contour data. DTM data will be of sufficient density to correctly portray all drainage, creeks, rivers and tributary streams, springs, falls and rapids, ponds, lakes, swamps, marshes, bogs, flood plains, rock cliffs, and other essential topographic features.
All well-defined natural drainage courses will be shown in accordance with Design Manual, Part 3. At 1”= 200’ (1:2000) and 1”= 100’ (1:1000) scale mapping, drainage lines will be stopped at a distance of 100 feet (30 m) from the ridge lines and drainage lines under 200 feet (60 m) in length need not be shown. At 1”= 50’ (1:500) scale mapping, drainage lines will be stopped at a distance of 50 feet (15 m) from the ridge lines and drainage lines under 100 feet (30 m) in length need not be shown.
E. Obscure Areas (with data). Where terrain is visible but obscured by vegetation, shadows or other limiting factors, an effort should be made to define the surface as accurately as possible. The area should then be outlined with a line on level 58 and labeled as obscured. A text file will be delivered with every project with a description that indicates that obscured areas may not meet map accuracy standards.
B.5-5
F. Obscure Areas (without data). Terrain completely obscured due to dense vegetation, dark shadows or other limiting factors will be outlined on level 56 and labeled as “Obscure Area.” No elevation data will be compiled. It is recommended that field surveys be performed to complete missing elevation data.
G. Symbols, Names and Graphic Quality. Major planimetric and topographic features will be in accordance with symbols designated in the Design Manual, Part 3. For large scale topographic maps, additional accepted standards for symbols, established by the Department, may be used to represent the features.
The name of cities, towns, villages, rivers, streams, railroads, and other features of importance will be obtained from available source maps and will be lettered on the map sheets. All state, federal and township roads will be numerically identified on the map sheets. Where applicable, both the State Route number and Traffic Route number, with symbolization, will be shown on the map sheet. All lettering will be legible and clear in meaning and will be positioned so it will not interfere with map features.
Line weights and symbology will be in accordance with the Design Manual, Part 3.
The Department has produced a document titled “Mapping Features and Standards” to aid in adherence to the Department graphics standards. Symbology as defined in MicroStation is outlined in this document along with other information.
H. Index Map. An index sheet will be required when the project area consists of eight (8) or more map sheets. The index map will show position and relationship of all map sheets to each other within the project area. The index sheet size will be consistent with the map sheet size utilized for the project. The map detail will be centered within the index sheet border. All necessary planimetric features will be drafted on the index map. Only major features, such as, cities and/or towns, roads, railroads, streams, etc, will be shown. The area, as stereo-compiled and drafted on the individual map sheets, will be outlined, to scale, on the index map. Where delineated or reduced width mapping is permitted, the outlined area should be representative of the exact compilation or reduced width. Each map sheet outlined will be numbered in accordance with the individual map sheet represented. A north arrow will be properly oriented and included with the index map. Symbols, line weights, and lettering sizes may be proportionally varied to the scale of the index map. B.6-1
CHAPTER 6
DIGITAL ORTHOPHOTOGRAPHY
6.0 INTRODUCTION
Digital orthophotography is a geospatially corrected digital image, correct in scale similar to digital mapping. The digital orthophotography process removes image displacement due to terrain relief and adjusts for lens distortion and camera orientation at the moment of exposure, to produce a photo with a scale that is uniform throughout. Since the rectified imagery is to scale, roadway alignments and other design features can be superimposed directly over the image file and produce hardcopy prints to scale. This chapter discusses procedures and specifications to be adhered to for the production of digital orthophotography.
Some projects may require digital orthophotography only for study or display purposes. For these projects, the following specifications could be reduced. The benefit of lowering the specifications would be a reduction of cost, man-hours, delivery time, and reduced image file size, all important issues to consider before starting any project that will require digital orthophotography. The project manager’s initial project request to the Photogrammetry & Surveys Section would require a written statement that the digital orthophotography does not need to meet design scale accuracies.
6.1 ORTHORECIFICATION
A. Aerial Photography. Aerial photography specifications will be as described in Part B, Chapter 2.
B. Ground Control. Placement of ground control is to be in accordance with Part B, Chapter 3, Targeting and Control Survey.
C. Aero-Triangulation Solution. An Analytical Aero-triangulation solution may be required as described in Part B, Chapter 4.
D. Image Scanning. Digital orthophotographic images must be produced from photo scans of equal or finer pixel ground resolution than the final ground pixel size required for the orthophotography. Pixel size for final orthophotography is as follows:
Ortho Scale, feet (meters) Pixel Size, feet (meters) 1” = 50’ (1: 500) 0.25’ (0.075) 1” = 100’ (1:1200) 0.50’ (0.150) 1” = 200’ (1: 2400) 1.00’ (0.40)
B.6-2 E. Digital Image Files. 1. Imagery is to be produced at a pixel rotation which will minimize non-image data (black or white areas) within final sheets. 2. Files are to be in standard arrangement with the upper left pixel set to (0,0). 3. CADD files are to be created in accordance with Part B, Chapter 5, Section 1 - Compilation. 4. All orthophotography sheets must edge match with no gaps. Overlap is acceptable if imagery blends seamlessly. 5. Individual orthophoto images of the project area shall be mosaicked and cut into sheets. Final deliverable files should not exceed 100 million pixels. If file size limitation is unacceptable, contact the Photogrammetry & Surveys Section.
F. Accuracy. Digital orthophotography imagery must meet or exceed accuracy specifications as stated in Part B, Chapter 7 - Digital Mapping Accuracy Testing.
G. Image Quality. 1. Final orthophotography must be adjusted for brightness and contrast to enhance visibility of fine detail and aesthetic quality of the imagery. 2. Final orthophotography must be inspected for blurs and other anomalies. 3. Image displacement of structures and bridges must be rectified by inclusion of additional breaklines collected on the structures surface. 4. Imagery must be compared to vector mapping (if available) or survey ground control to ensure proper geospatial referencing and accuracy is obtained.
H. Digital Terrain Models (DTM). DTM’s are to be compiled in accordance with Part B, Chapter 5, Section 2. D. - Spot Elevations, E. – Digital Terrain Models and Topography, and F. – Obscure Areas.
I. Format. Digital orthophotography image files will be produced in both formats as follows: 1. One set of orthophotography image files will be in a format that will facilitate geospatial referencing into MicroStation 95 or later and will be geospatially referenced into Intergraph IRASC software uncompressed. 2. A second set of orthophotography files will be delivered in a standard TIFF format uncompressed.
All orthophotography files must be delivered to the Department in the above stated formats unless prior written approval for an alternative format is given by the Photogrammetry & Surveys Section. B.7-1
CHAPTER 7
DIGITAL MAPPING ACCURACY TESTING
7.0 INTRODUCTION
This chapter defines spatial accuracy requirements for digital mapping projects. Horizontal and vertical accuracy requirements are based on standards developed by the American Society for Photogrammetry and Remote Sensing (ASPRS). Section 7.1 - Accuracy discusses these established accuracy requirements. Section 7.2 - Map Accuracy Test establishes procedures for verifying these horizontal and vertical accuracies. Information provided is based on data from the Federal Geodetic Control Subcommittee (FGCS).
7.1 ACCURACY
The American Society for Photogrammetry and Remote Sensing (ASPRS) has published "Accuracy Standards for Large Scale Maps." These standards were developed by the Specifications and Standards Committee of ASPRS and were approved by the Professional Practices Division in March 1990. These ASPRS standards are extremely beneficial in that they indicate accuracy levels at ground scale. Thus, digital spatial data of known ground scale accuracy can be related to the appropriate map scale for graphic presentation at a recognized standard.
These standards define the spatial accuracy requirements for large-scale topographic maps prepared for special purposes or engineering applications. Emphasis is on the final spatial accuracies that can be derived from the map in terms most generally understood by users.
A. Horizontal Accuracy. Horizontal map accuracy is defined as the Root Mean Square (RMS) error in terms of the project's planimetric survey coordinates (X, Y) for checked points as determined at full (ground) scale of the map. RMS error is the cumulative result of all errors including those introduced by the processes of ground controls surveys, map compilation, and final extraction of ground dimensions from the map. The limiting RMS errors are the maximum permissible RMS errors established by this standard. These limiting RMS errors for Class 1 maps are tabulated in Table 7.1.1 along with typical map scales associated with the limiting errors. It should be noted that these limiting errors are only applicable to tests made on well-defined points.
B.7-2
Table 7.1.1 Planimetric Coordinate Accuracy Requirements for Well-Defined Points - Class 1, Maps
PLANIMETRIC (X OR Y) ACCURACY
TYPICAL MAP SCALE, feet (meters) LIMITING RMS ERROR, feet (meters)
1”= 50’ (1:500) 0.5’ (0.125) 1”= 100’ (1:1000) 1’ (0.25) 1”= 200’ (1:2000) 2’ (0.50)
B. Vertical Accuracy. Vertical map accuracy is defined as the RMS error in elevation in terms of the project's elevation datum for well-defined points only. For Class 1 maps, the limiting RMS error in elevation is set by the standard at one-third the indicated contour interval for well-defined points only. Spot heights will be shown on the map within a limiting RMS error of one-sixth of the contour interval.
Although contours are no longer required as a deliverable, a contour interval is reported in the title block. The contour interval defines the vertical accuracy of the product and is the guideline for later production of contours from the DTM. Spot heights are no longer required, but the limiting RMS error (one sixth contour interval) is a good guideline for random points within the DTM.
C. Lower Accuracy Maps. Map accuracies can also be defined at lower spatial accuracy standards. Maps compiled within limiting RMS errors, of two or three times those allowed for under a Class 1 map will be designated as Class 2 or Class 3 maps, respectively. A map may be compiled that complies with one class of accuracy in elevation and another class of accuracy in plan. Multiple accuracies on the same map are allowed provided a diagram clearly relating segments of the map with their appropriate map accuracy class is included for submission.
The Department will ascertain and establish the need for a Class 1, Class 2, or Class 3 map on a "project by project" basis, and will convey to the photogrammetric contractor its choice before the photographic fight mission has been carried out.
7.2 MAP ACCURACY TEST
A "map accuracy test" will be required for all map sheets produced. Testing for horizontal accuracy compliance is accomplished by comparing the planimetric (X and Y) coordinates of well-defined ground points to the coordinates of the same points as determined by a horizontal check survey of higher accuracy. The check survey will adhere to the accuracy requirements outlined in "Standards and Specification for Geodetic Control Networks" by B.7-3 the Federal Geodetic Control Subcommittee (FGCS). The check survey will be designed in order to achieve standard deviations equal to or less than one-third of the "limiting RMS error" selected for the map. The distance between control points used in the FGCS standard for the design of the survey will be the horizontal ground distance across the diagonal dimension of the map sheet.
Testing for vertical accuracy compliance is accomplished by comparing the elevations of well-defined points as determined from the map to their corresponding elevations determined by a survey of higher accuracy. For purposes of checking elevations, the map position of the ground point may be shifted in any direction by an amount equal to twice the limiting RMS error in position. The vertical check survey should be designed to produce RMS errors in elevation differences at check point locations no larger than 1/20th of the contour interval. The distance between benchmarks used in the FGCS standard for the design of the vertical check survey will be the horizontal ground distance across the diagonal of the map sheet. Generally, vertical control networks based on surveys conducted according to FGCS standards for Third Order provide adequate accuracy for conducting the vertical check survey.
Discrepancies between X, Y, or Z coordinates of the ground point, as determined from the map and by the check survey, that exceed three times the "limiting RMS error" will be interpreted as blunders and will be corrected before the map is considered to meet this standard.
The same survey datums, both horizontal and vertical, must be used for both project and check control surveys. Although a national survey datum is preferred, a local datum is acceptable.
The Photogrammetry & Surveys Section determine the number and location of check points required on a per project basis.
Maps produced according to this spatial accuracy standard will include the following statement in the title block:
"THIS MAP WAS COMPILED TO MEET THE ASPRS STANDARD FOR CLASS 1 MAP ACCURACY.”
If the map was checked and found to conform to this spatial accuracy standard, the following statement will also appear in the title block:
"THIS MAP WAS CHECKED AND FOUND TO CONFORM TO THE ASPRS STANDARD FOR CLASS 1 MAP ACCURACY.”
Since most mapping is not map tested until after delivery, the Photogrammetry and Surveys Section will contact the requestor in the event of a test failure. Otherwise, successful test results will be archived in Photogrammetry and Surveys Section project folder. B.8-1
CHAPTER 8
ELECTRONIC MEDIA PREPARATION AND ARCHIVING
8.0 INTRODUCTION
The objective of this chapter is to establish the procedures for preparing, handling, and archiving all electronic mapping files for photogrammetric mapping projects.
8.1 ELECTRONIC FILE TRANSFER
The "Photogrammetry and Surveys Section" will be responsible for copying and transferring of all in-house compiled mapping files. All design consultant requests received by the "Photogrammetry and Surveys Section” for in-house mapping files will be performed upon receipt of written approval from the appropriate Engineering District office. All materials furnished by the Department and any other materials produced in conjunction with the project will be returned to the District upon completion of the project. All files will be compatible with MicroStation design file format.
8.2 ELECTRONIC FILE ARCHIVING
All electronic mapping files will be submitted to the Department in MicroStation compatible design file format. All Department mapping files will be "backed-up" using the current electronic media. This "backed-up" copy of the mapping file will then be stored at any of the Department approved, off-site locations for archiving purposes.
All aerial film will be returned to the Department for archiving at the Photogrammetry and Surveys Section’s office. Additionally, all film flown by or for the Department will be scanned for digital archiving. Digital photography will be grouped according to spring (January to June) and fall (July to December) seasons and archived on the current electronic media to be kept off site. This should occur twice per year after each season’s photography is complete. APPENDICES
TABLE OF CONTENTS
APPENDIX SUBJECT PAGE
A..GLOSSARY of TERMS…………………...... …. A-1
B..FRONT PAGE ...... … B-1 ALIGNMENT, CONTROL TRAVERSE SKETCH ...... …B-2 ALIGNMENT, CONTROL POINT SKETCH ...... … B-3 ALIGNMENT, CENTERLINE ALIGNMENT ...... … B-4 TOPOGRAPHY, CONVENTIONAL METHOD ...... ………B-5 TOPOGRAPHY, TOTAL STATION METHOD ...... ………B-6 TOPOGRAPHY, REFERENCE POINT SKETCH ...... ….B-7 TOPOGRAPHY, ELECTRONIC DATA COLLECTOR INDEXING ...... B-8 CROSS SECTIONS, CONVENTIONAL METHOD ...... ………B-9 CROSS SECTIONS, TOTAL STATION METHOD ...... ………B-10 PROFILES, CONVENTIONAL METHOD ...... ………B-11 PROFILES, TOTAL STATION METHOD ...... … B-12 BENCH LEVELS ...... ………B-13
C..GRADE SHEET ...... … C-1 COMPUTATION OF EARTHWORK……………………………………. C-2 RECORD OF CONTROL - HORIZONTAL ...... … C-3 RECORD OF CONTROL - VERTICAL ...... …..C-4
D..QUALITY ASSURANCE/QUALITY CONTROL PLAN for DEVELOPMENT of RIGHT-OF-WAY & CONSTRUCTION PLANS ... D-1 .D-1 PROCEDURES and GUIDELINES……… ...... … ... ….D-2 PRE-SURVEY ACTIVITIES…………………………………………..….D-2 FIELD SURVEY ACTIVITIES……………………………………………D-2 FINAL DESIGN ACTIVITIES……………………………………… ... ….D-4 FIELD SURVEY INFORMATION REQUIRED for STRUCTURES... ….D-5 PURPOSE of HYDRAULIC SURVEY……………………………… .. ….D-6 SURVEY BOOK & FIELD NOTE FORMAT (FORM D-428)……….. ….D-8 APPENDIX A
GLOSSARY OF TERMS
APPENDIX A-1
Accuracy - is the degree of closeness, or conformity, of measurements to their true value.
Alidade - is the top portion of a theodolite designed to provide precision to the table of the instrument.
Arc-Definition - is the relationship between the radius, R, and the degree of curve, D, for a circular curve. The degree of curve, D is defined as the central angle which subtends a 100 ft arc. R = 5,729.58/D.
Assumed Plane Coordinates - is a coordinate system based on either a rectangular surface or a flat surface. Assumed plane coordinates are represented by an arbitrary grid system.
Bifurcated - is a descriptive term used with highways for divided baselines.
Cartesian - is a plane coordinate system forming a grid. The system defines an 'X' axis (also represents easting values) and a 'Y' axis (also represents northing values) to establish the grid.
Chord-Definition - is the relationship between the radius, R, and the degree of curve, D, for a circular curve. The degree of curve, D is defined as the central angle which subtends a 100 ft chord. R = 50/sin 1/ D.
Class - is a division or grouping within a specific order.
Compass Rule - is an adjustment procedure performed for the balancing of a control traverse. The compass rule applies corrections to latitudes and departures in proportion to the distances of each course. It should be noted that the compass rule assumes that all angles and distances have been measured with equal precision.
Digital Elevation Model – an electronic file containing x, y, and z coordinate points. These files can be used in modeling software to generate contours.
Digital Terrain Model (DTM) – an electronic file containing breaklines and points consisting of x, y, and z coordinates. DTM’s are preferred over digital elevation models (DEM)because they include breaklines. Breaklines tell the software where there are defined changes in grade. DEM’s only include individual points. DTM’s files can be used in modeling software to generate contours at the specified intervals.
Double-Centering - is a method of aligning the vertical cross hair of a conventional transit.
Eastings - are the "X" values of coordinates represented on a plane coordinate system.
Geodetic - is a coordinate system established by the shape of the earth, or a large part of its surface.
APPENDIX A-2
(GPS) Global Positioning System - is a three-dimensional, satellite surveying system based on observations of radio signals of the NAVSTAR Global Positioning System. These observations are reduced to establish their equivalent Cartesian coordinates (X,Y,Z). These coordinates can then be converted to geodetic coordinates (latitude, longitude, and height- above-reference ellipsoid).
"Hard" Conversion - is a procedure to develop a new rounded, rationalized metric number computed from a US conventional measurement.
Least Squares Method - is an adjustment technique performed for the balancing of survey data. Least square adjustments are often performed for bench level circuits and control traverses.
Monumentation - is the act of referencing specific control points throughout a survey project.
(NAD 27) North American Datum of 1927 - is the second horizontal geodetic datum (first – North American Datum) of continental extent in North America. It was originally established by the US Coast and Geodetic Survey (USC&GS).
(NAD 83) North American Datum of 1983 -is the third horizontal geodetic datum of continental extent in North America. It was established by the National Geodetic Survey (NGS) of the United States, the Geodetic Survey of Canada (GSC), and the Danish Geodetic Institute (responsible for surveying in Greenland).
(NAVD 88) North American Vertical Datum of 1988 - is a vertical reference system used to establish vertical control in Pennsylvania after January 1, 1996.
(NGRS) National Geodetic Reference System - is a compilation of all current control points and their respective coordinates established by the National Geodetic Survey (NGS).
(NGS) National Geodetic Survey - is the governing organization within the continental United States mainly responsible for establishing control points and reference systems.
(NGVD 29) National Geodetic Vertical Datum of 1929 - is a vertical reference system used to establish vertical control in Pennsylvania prior January 1, 1996.
Northings - are the "Y" values of coordinates represented on a plane coordinate system.
Order - is a division or grouping of specific accuracy requirements.
Parallax Errors - are apparent focusing flaws as a result of a maladjusted instrument.
Precision - is the degree of consistency among a group of measurements.
APPENDIX A-3
Rounding - is a methodology to discard non-significant digits.
Sexagesimal System - is a system established by the number 60. All angular measurements in surveying are based on the sexagesimal system.
Significant Figures - is the number of sure or certain digits, plus one estimated digit.
"Soft" Conversion - is an exact re-stating of a US conventional measurement in its equivalent metric term.
(SPCS 27) State Plane Coordinate System of 1927 - is the original plane coordinate mapping system established for the United States by the US Coast and Geodetic Survey (USC&GS).
(SPCS 83) State Plane Coordinate System of 1983 - is the plane coordinate mapping system adopted in Pennsylvania after January 1, 1996. It incorporates both the North American Datum of 1983 (NAD 83) information and the North American Vertical Datum of 1988 (NAVD 88) information.
(SPCS) State Plane Coordinate System - is a coordinate system developed for each particular state. Within each SPCS, a central meridian, an origin, and a rectangular coordinate grid has been developed by the National Geodetic Survey (NGS).
Stationing - is a standard system of marks established at set (measured) distances along a line.
Swing Tie - is a method of referencing control and alignment points to fixed topography. A minimum of three (3) fixed topographic features are established radial to the point being referenced.
Two Peg Test - is a common procedure used to adjust the horizontal cross hair of a leveling instrument.
Truncate - is a methodology to discard non-significant digits.
(USC&GS) US Coast and Geodetic Survey - is the governing organization responsible for determining the geodetic positions (latitudes and longitudes) of monumented points throughout the United States.
(USGS) US Geological Survey - is the governing organization within the United States responsible for preparing maps of the entire country.
US Survey Foot - is the conversion factor (1200 m / 3937 ft) applied to a US conventional measurement in terms of feet to obtain the metric equivalent in terms of meter. One (1) US survey foot equals 1200/3937 meters.
APPENDIX B
SAMPLE FIELD BOOK ENTRIES
APPENDIX B-1
Figure B.1 - Front Page
APPENDIX B-2
Figure B.2 – Alignment, Control Traverse Sketch
APPENDIX B-3
Figure B.3 – Alignment, Control Point Sketch
APPENDIX B-4
Figure B.4 – Alignment, Centerline Alignment
APPENDIX B-5
Figure B.5 – Topography, Conventional Method Figure B.5 – Topography,
APPENDIX B-6
Figure B.6 – Topography, Total Station Method Figure B.6 – Topography,
APPENDIX B-7
Figure B.7 – Topography, Reference Point Sketch Figure B.7 – Topography,
APPENDIX B-8
Figure B.8 – Topography, Electronic Data CollectorFigure B.8 – Topography, Indexing
APPENDIX B-9
Figure B.9 – Cross Sections, Conventional Method
APPENDIX B-10
Figure B.10 – Cross Sections, Total Station Method
APPENDIX B-11
Figure B.11 – Profiles, Conventional Method
APPENDIX B-12
Figure B.12 – Profiles, Total Station Method
APPENDIX B-13
Figure B.13 – Bench Levels
APPENDIX C-1
GRADE SHEET
Page ______Of ______Bureau
of County ______Design
Route, Sec______Seg, Off______Twp, Boro, City______
Distance from Stake to Center Line of Elevation of Top of Elevation of Finished Top of Stake to Finished Grade Station Proposed Roadway Stake Grade at Center Line Cut Fill Left Stake Right Stake
Prepared By ______
Checked By ______
FORM D-413 REV 12-01
APPENDIX C.2 COMMONWEALTH OF PENNSYLVANIA
DEPARTMENT OF TRANSPORTATION
COMPUTATION OF EARTHWORK
STATE PROJECT NUMBER DATE PAGE of SUB SYS SR PROJEC PHA SECTION DIST CO SECTIO T ROUTE N APPL COUNTY No. TOWNSHI P BORO.
STANDARD ROADWAY CUT FILL STATION AREA CUBIC FEET TOTAL AREA CUBIC FEET TOTAL REMARKS
TOTALS
COMPUTED BY
FORM D-412A REV 02/02 PREPARED BY
APPENDIX C-3
COMMONWEALTH OF PENNSYLVANIA DEPARTMENT OF TRANSPORTATION
RECORD OF SURVEY CONTROL - HORIZONTAL
STATION NAME: C999 PROJECT SR: 4004-000 COUNTY: NORTHUMBERLAND
GENERAL INFORMATION Locality: Altoona, PA USGS Quad Name: Hershey, PA Established By: PennDOT Date Established: 1998 Type of Mark: Brass Disk in Conc. Mon. Stamping: “ANNIE 1992” SPECIFICATIONS Horizontal Control Derived By: GPS Horizontal Order Accuracy: First Vertical Control Derived By: Differential Vertical Order Accuracy: Third Horizontal Datum: NAD83 (1992) Vertical Datum: NAVD88 HARN TIES HARN Stations that derived this station’s original position: GOSPEL HILL RM 2, WIL1 CORS, CONCORD RESET RM 4 NGS VERTICAL TIES NGS Benchmarks that derived this station’s original elevation: GEODETIC COORDINATES Latitude: 40 00’ 00.12345” N Ellipsoidal Height (Meters): 100.12 Longitude: 75 00’ 00.12345” W Ellipsoidal Height (US FT): 328.48 Convergence: -0 00’ 00.1” NGS Geoid Model Type: GEOID99 PA STATE PLANE COORDINATES - NORTH ZONE Northing (Meters): 123456.789 Northing (US FT): 405041.149 Grid Scale Factor: 0.987654321 Easting (Meters): 123456.789 Easting (US FT): 405041.149 Elevation Scale Factor: 0.987654321 Elevation (Meters): 100.123 Elevation (US FT): 328.487 Combined Scale Factor: 0.987654321 AZIMUTHS Companion Station: C998 Secondary Azimuth Mark : Cell Tower Antenna Grid Azimuth: 00 00’ 00” Secondary Grid Azimuth: 00 00’ 00” Grid Distance (Meters): 100.123 Description: Grid Distance (US FT): 328.487 Combined Factor: 0.987654321 Description: PennDOT Monument REFERENCE TIES Number Type of Reference Mark Meters US FT 1 0.123 0.40 2 0.123 0.40 3 0.123 0.40 TO REACH DESCRIPTION & SKETCH To reach the station from the intersection of
APPENDIX C-4
COMMONWEALTH OF PENNSYLVANIA DEPARTMENT OF TRANSPORTATION
RECORD OF SURVEY CONTROL - VERTICAL
STATION NAME: CIH 24 PROJECT SR: 4004-000 COUNTY: NORTHUMBERLAND
GENERAL INFORMATION Locality: Altoona, PA USGS Quad Name: Hershey, PA Established By: PennDOT Date Established: 1998 Type of Mark: Brass Disk in Bridge Abutment Stamping: “HARPSTER”
SPECIFICATIONS Horizontal Control Derived By: Hand-Held GPS Horizontal Order Accuracy: N/A Vertical Control Derived By: Differential Vertical Order Accuracy: Third Horizontal Datum: NAD83 / WGS84 Vertical Datum: NAVD88
NGS VERTICAL TIES NGS Benchmarks that derived this station’s original elevation: GOSPEL HILL RM 2, A 323, M 6
GEODETIC COORDINATES Latitude: 40 00’ 00” N Longitude: 75 00’ 00” W
ELEVATION - NAVD88 Elevation (Meters): 100.123 Elevation (US FT): 328.487
TO REACH DESCRIPTION, DESCRIPTION OF MARK & SKETCH To reach the station from the intersection of
The station is a
APPENDIX D
QUALITY ASSURANCE/QUALITY CONTROL PLAN FOR DEVELOPMENT OF RIGHT-OF-WAY & CONSTRUCTION PLANS
APPENDIX D-2 Procedures and Guidelines
Pre-Survey Activities
Review project scope of work. Obtain tax map from County Tax Office. Research all deeds of properties that adjoin proposed survey area and obtain all called for recorded retracement or subdivision plats. Research all turnbacks, abandonments, local roads, railroads and Highway Occupancy Permits. If necessary, contact licensed Pennsylvania Professional Land Surveyor who conducted adjoining property surveys and acquire plats or plans of survey. Obtain all previous right-of-way records and/or plans such as right-of-way, as built, and road dockets. Obtain any previous PennDOT or PDH survey books. Obtain existing horizontal and vertical control data within project area.
Field Survey Activities
Field view project site. ___ Establish horizontal and vertical control on the project site in accordance with Part A, Chapter 4 of this manual. In the field, establish legal right-of-way baseline/centerline using reference ties and old geometry from right-of-way plans and/or survey books. Use valid recorded alignment stationing for longitudinal stationing. Use RMS Segment and Offset if as- built plans do not exist. Correct legal right-of-way baseline/centerline must be established, if record alignment exists. Re-established alignment must conform to reference ties. There is an obligation to use old, existing, preliminary reference ties in absence of superior evidence. If as-built alignment was monumented, the monuments could define alignment in location other than centerline of pavement. Consideration must be given to the typical sections on as-built plans that may show relationship of baselines to what was built or widened on only one side of the roadway. If as-built alignment was not monumented but contains preliminary or swing ties, alignment must be established that will conform to all existing evidence (e.g. topographical, extrinsic evidence, property pins, if confirmed). If, and only when no other evidence exists (such as recorded instruments or field evidence), then centerline of existing roadway (beaten path) may be used, even when creating first time geometry. Established legal right-of-way baseline and/or centerline shall be tied geometrically (by field angles and distances) to survey baselines and traverses.
APPENDIX D-3 Any alignment produced must be developed to conform to the correct legal right-of- way alignment, if extended to major control points beyond the limits of authorization. Any alignment, either inside or outside areas of authorization, must be developed to conform to legal right-of-way both longitudinal and transversely. Permanent alignment references shall conform to Part A, Chapter 4.3 of this manual. ___ By state law, when using the Pennsylvania State Plane Coordinate System, the North American Datum of 1983 (NAD 83) will be used. The complete reference frame of this datum that was used is recommended to be noted, such as NAD 83 (92) when the survey was tied to control of the state’s High Accuracy Reference Network (H.A.R.N.), or NAD 83 (CORS96) when the survey was tied to CORS stations recognized by the National Geodetic Survey (NGS), or even NAD 83 (NSRS2007) when the survey was tied to control published by the NGS as National Spatial Reference System 2007 coordinates. It is strongly recommended to note the Combined Factor used when using State Plane Coordinates. The superseded North American Datum of 1927 (NAD 27) may only be used for exceptional reasons and only with the concurrence of the District Survey Manager. ___ By Department policy, the vertical datum to be used for Bench-Mark elevations will be the North American Vertical Datum of 1988 (NAVD 88). It is strongly recommended that all Bench-Mark elevations be established by differential leveling, with such notes entered in Form D-428 (survey field book) along with detailed to-find descriptions, such as ties to segment and offsets. Other methods to establish Bench- Mark elevations and any decision to use the superseded National Geodetic Vertical Datum of 1929 (NGVD 29) will only be done with the concurrence of the District Survey Manager. Assumed or arbitrary horizontal and vertical datum shall not be used without prior approval of the District Survey Manager. All assumed coordinate and vertical data shall be on the same base datum (e.g. bridge and roadway). Topography - detailed description to include utility names and pole ID numbers, signs (type and description), guide rail (types and end treatment), drainage (size and types), existing property corners and physical lines of property possession, permanent buildings (including type of structure), all permanent improvements constructed by the occupier of the property as per the Part A, Chapter 4 and traffic line patterns. Field verification of vertical accuracy shall be accomplished by obtaining “check” observations of previously established bench-marks and/or traverse or mapping control points at each instrument set-up during topographic data collection. To uncover blunders, conventional cross-sections or check profiles may be run if any errors are found in the digital terrain model (DTM) produced. NGS (previously USC&GS), USGS, PennDOT/PDH monuments - locate/describe existing monuments. If monument(s) will be affected, contact appropriate NGS/USGS and/or District Survey Manager and reference in accordance with appropriate agency policies. Bridge data (designer to request survey), see Attachment A. All field notes shall be recorded legibly in Form D-428, see Attachment B.
APPENDIX D-4 Final Design Activities
Right-of-way breaks on property lines should be avoided. If required to be on property lines, the property line or lines must be confirmed by field survey. Referencing required right-of-way lines to spiraled roadway alignments shall be avoided. Right- of- way lines shall not be developed that are concentric and parallel to spiral geometry. Survey and right-of-way alignments with simple curves and tangents shall be used. G.P.S. requirements should be confirmed by reviewing with the District Survey Manager. G.P.S. activity shall comply with Part B, Chapter 3.3 of this manual. Plan references and ties must exist to permit the re-establishment of the legal right-of- way alignment. A licensed Pennsylvania Professional Land Surveyor shall direct the deed plotting and compilation process. Existing property lines and corners located by the field survey shall be given careful consideration during this process. ___ All found property line monumentation is recommended to be tied to the right of way baseline/centerline alignment by station and offset. Review right-of-way lines with the Pennsylvania Professional Land Surveyor in charge of the project. Review control references and right-of-way line break point monumentation with District Survey Manager. Check validity and accuracy of coordinate tables for roadway controls and bridge stake out work points. When Pennsylvania State Plane Coordinates are used, the combined factor shall be noted in the general notes and in the project coordinate tabulations. If a combined factor was not used, explicitly note that information. All alignments shall be established at 50 feet (15 m) intervals or at major control points, referenced with permanent monuments Part A, Chapter 4.2 and recorded in Form D-428 as per Appendix B-4 of this manual. ___ All intersecting alignments shall be geometrically tied to mainline; station and skew angle shall be noted “On curves, skew angle shall be tangent to curve.” ___ Reference vertical control with permanent benchmarks outside areas of construction by differential leveling. Space benchmarks approximately every 1000 feet (300 m) throughout the project. There must be a minimum of two benchmarks per project. Enter with detailed descriptions tied to segment and offset in Form D-428 (field book). See Appendix B-13, of this manual and Benchmark Reset procedures published by NGS. Review status of any existing affected associated right-of-way plans (e.g. dedications, donations, viewers' plans, vacations, abandonments, navigable streams, etc.).
APPENDIX D-5
Field Survey Information Required for Structures ____ Collect enough topographic data to create a digital terrain model (DTM) in the area affected by the structure (the structure may be raised and approaches may be adjusted). Pay particular attention to modeling the stream bed capturing the thalweg, all significant changes in slope, scour holes, gravel bars and debris piles. Conventional stream baseline, stream cross-sections and stream profile may be use in lieu of a DTM with the District Survey Manager concurrence. ____ Areas outside of the DTM where hydraulic cross-sections are needed can be collected by total station or by GPS RTK observations. The observed points must be established such that they can be used to construct a cross-section that is perpendicular to stream flow and the direction of flow in the floodplain (perpendicular to contour lines). Where the channel meanders through the floodplain, broken or dog-leg sections may be necessary. All subsections of a cross-section so created should be straight lines. Cross-sections should not overlap. More points should be surveyed in the channel than in the floodplain. The points surveyed comprising a cross-section should be so noted in the survey field book. ____ If using conventional procedures orient baseline along stream with stations running downstream and making Station 10+00 (3+000) approximately the center of the bridge. Locate the channel from the baseline so the alignment of the stream is obtained. ____ Obtain pier dimensions and shape so we can determine the amount of obstruction within the stream. ____ Obtain elevations of the bottom of beams at each contact with substructure members (needed for both fascia beams), more points may be needed if irregular, (e.g. Arch). ____ Obtain sufficient elevations along the profile of the channel (elevation spacing to be no more than 50 feet (15 m) apart) so that an average slope may be obtained. ____ Full cross-sections; hydraulic section perpendicular to stream flow; show angle off baseline, if a baseline is used. (a) Minimum 500 feet (150 m) upstream and 500 feet (150 m) downstream (b) At each face of structure (we need an elevation of the bottom of beam and the top of roadway for each point along the ground where an elevation is taken). ____ Locate the toe of a wingwall or any break point near the structure that shows a change from the main stream section to the face of structure section. ____ Locate any location where another stream joins the main stream channel (one immediately downstream; one immediately upstream from the tributary intersection). ____ Locate any change in typical section such as a narrowing of channel, change of slope, etc. ____ When possible, extend DTM or cross-sections to elevations approximately 10 feet (3 m) above the deck. ____ Stream cross-sections shall be at 90° to stream flow except for sections at face of structure. Sections at face of structure and at ends of wingwalls must be parallel to centerline of road.
APPENDIX D-6 ____ Note elevations of located physical features such as edge of road, edge of stream, wingwalls, woods, etc. ____ Note type of ground cover and changes in ground cover on hydraulic cross-sections such as dense brush, woods, lawn, goldenrod, and weed field, etc. ____ At bends in a stream outside of DTM, take one cross-section just above bend and one just below bend. ____ Always take one hydraulic cross-section located one span length upstream from upstream bridge opening. This section is required to perform scour estimates for proposed structure. ____ If a multi-span bridge, the upstream cross-section should be located upstream the total of span lengths. For example: two spans @ 60 feet (20 m) each, locate upstream cross-sections 120 feet (40 m) above bridge site.
Purpose of Hydraulic Survey
The quantity of water that will flow through a channel area is calculated based on historical data of the amount (in inches) of rain falling in a time period and the frequency (in years) of occurrences. The rate combined with the total drainage area allows us to calculate the amount of water that will flow through the channel and under/over the bridge. The slope of the channel is critical, since this will help determine the velocity of the water. The steeper the slope, the faster the water flows, allowing more water to flow through a channel section. This illustrates why we need the various sections. We do not want to raise water elevations when comparing existing and proposed bridges. The four cross-sections at the bridge, the profile of the road, and the pier shapes and sizes are needed to determine the effects the bridge has on the stream flow and water elevations. This information is entered into a computer model so that the water surface elevations for different storm frequencies can be computed. Our bridges are typically designed for a 50-year storm, a storm that occurs once every 50 years. The Department’s goal is to provide a new structure with the low chord elevation two feet higher than the design storm elevation, or one foot higher than the 100-year risk assessment storm, whenever possible. The information needed for the stream survey is just like that required for a road survey. Any change in alignment, size, shape, slope, or any obstruction that will impede the flow of water or that may change the water course or elevation must be recorded.
APPENDIX D-7
0 M 0 15
0 M 0 15
15 M 0
APPENDIX D-8 Attachment B
Survey Book & Field Note Format (Form D-428)
____ All field survey books should use a format and index consistent with our Form D-428.
____ Index should include all separate activities performed by stationing (e.g. alignment, control points, traverse and closure, benchmark level runs, segment/offset reference to project station, basis of bearing, and reference or ties to re-establish line).
____ Contents should include sketches for all alignments, sketches for preliminary ties, coordinates for control points and sketches of control traverses/baselines and/or GPS networks.
____ Recorded documentation should include sufficient data to establish all project horizontal and vertical control easily and accurately.
____ Establish control points in the field, occupy, record angles, and determine equalities where necessary, including references. “Paper Points” are not acceptable.
____ Page one should contain the surveyor’s report, list major items encountered during the survey (e.g. plans used, horizontal and vertical datums, combined factor, existing controls held to produce alignments/traverses, property corners or monuments used, bearing datum, State Plane or arbitrary coordinates, RMS stations and conversion to segment and offsets, and other pertinent information). This information may be of assistance to designers or surveyors during project site visits.
____ Comply with Part A, Chapter 1 of this manual.
____ Survey data collected via electronic data collectors files shall be referenced in the survey field books and the electronic data files will be considered a part of the survey field book and will be delivered with the survey field book.