FOR 274: Forest Measurements and Inventory
Lecture 5: Principals of Surveying • An Introduction to Surveying • Horizontal Distances & Angles
An Introduction to Surveying: Social and Land
In Natural Resources we survey populations to gain representative information about something
We also conduct land surveys to record the fine-scale topographic detail of an area
We use both kinds of surveying in Natural Resources
An Introduction to Surveying: Why do we Survey?
To measure in the field the distance, bearing, and location of features on the Earth’s surface
Geodetic Surveying • Very large distances • Have to account for curvature of the Earth! Plane Surveying • What we do • Thankfully regular trig works just fine
1 An Introduction to Surveying: Why do we Survey?
Foresters as a rule do not conduct many new surveys BUT it is very common to: • Retrace old lines • Locate boundaries • Run cruise lines and transects • Analyze post treatments impacts on stream morphology, soils fuels,etc In addition to land survey equipment, Modern tools include the use of GIS and GPS Æ FOR 375 for more details
An Introduction to Surveying: Types of Survey
Construction Surveys: collect data essential for planning of new projects - constructing a new forest road - putting in a culvert Hydrological Surveys: collect data on stream channel morphology or impacts of treatments on erosion potential
An Introduction to Surveying: Types of Survey
Topographic Surveys: gather data on natural and man-made features on the Earth's surface to produce a 3D topographic map
Typical Steps include: - Establish horizontal & vertical controls - Locating features that may be wanted by the survey - Compute distances, angles, and elevations
2 An Introduction to Surveying: Types of Survey
Land Surveys: establish boundaries, locations, and tracts of land in a given area
Typical Steps include: - Establish markers or monuments in order to produce a historical reference for ownership boundaries in the future - Relocate previous legally established markers (visit survey records and retrace steps) - Subdivide estates into parcels of predetermined sizes and shapes - Calculates areas and prepare a deed
An Introduction to Surveying: The Main Points
Forestry surveying does not need engineering precision equipment - It is rare that 1/10” accuracy is needed However, although less $$$ the equipment we do use is still very accurate
An Introduction to Surveying: The Main Points
When surveying: - Carefully plan the Survey - It is difficult to find forgotten equipment A survey can be ruined by: 1 missing point 1 incorrectly recorded point Include in your plan ways to double check your data!!!
3 Land Surveying: Horizontal Distances & Angles
Typical Surveying Instruments • Chains and Pacing • The Transit • The Theodolite or Total Station • Laser Rangefinders
Measuring Horizontal Distance: The Chain
The chain (66 feet) is the fundamental unit of horizontal measurement used by foresters It is also called the surveyor’s or Gunter’s chain 1 Cha in = 100 Lin ks All distances in US Land surveys are in chains and links 1 sq mile = 80 x 80 chains
Measuring Horizontal Distance: The Chain
A Chain can be measured with: Pacing The Hip Chain Surveyor’s Chain or Rope Large tapes
4 Measuring Horizontal Distance: The Chain
Pacing out a chain is one of the simplest and most useful assets for a timber cruiser Expert pacers are accurate to 1 foot in 80 on level terrain A pace is commonly defined as two natural steps – i.e. each time the same foot touches the ground
Measuring Horizontal Distance: Traditional Chaining • Need head chainman and rear chainman • Head chainman places a starting pin • On level terrain the head chainman pulls out chain (or tape) - checks & maintain bearing!!! • When the end of the chain or tape is reached at the rear – the rear chainman shouts “chain”
Measuring Horizontal Distance: Traditional Chaining •The tape is held taught and the rear chainman shouts “stick” • The head chainman puts in a pin and shouts ”stuck” • The rear chainman picks up the 1st pin and walks to the 2nd pin
This process is repeated as necessary.
5 Measuring Horizontal Distance: Tape Graduation
Steel tapes are 1-2 chain long and graduated in links 1 chain and 84 links is reported as: 1.84 chains
Tapes with an additional link beyond the zero end are called “adding tapes”. This additional link allows 1/10 link measures:
9 8 7 6 5 4 3 2 1 |ZERO 1|LINK 8|7
87.5 links
Measuring Horizontal Distance: Tape Graduation
Tapes with an additional link beyond the last link are called “subtracting tapes”.
9 8 7 6 5 4 3 2 1 |LINK 8|8
87.5 links
Adding tapes are generally preferred as less people make errors
Measuring Horizontal Distance: Chaining
What do you think are the main sources of error in measuring distance by chaining?
• Not keeping the chain or tape taut • SihSnagging the tape on bhbranches • Not following the correct bearing • Mistakes in counting how many pins have been used • Reading and Recording the wrong numbers
6 Land Surveying Equipment: The Theodolite
A Theodolite measures both horizontal and vertical angles Transits are specialized Theodolites that have a telescope that can “flip over or transit the scope” to allow back-sighting
Land Surveying Equipment: It’s all Trigonometry
We know the angles and the X size of reference bar (via sight in telescope) Y From trig we can get X and Y: Remember SOH, CAH, TOA sin(angle) = bar/Y cos(angle) = X/Y tan(angle) = bar/X
Land Surveying Equipment: Laser Rangefinders
Laser rangefinders use this relationships to calculate distance:
Distance = speed of light * (time/2)
The time refers to time of pulse to go from the instrument to the tree and back again
7 Land Surveying Equipment: Total Stations
Total Stations are essentially a combination of a Theodolite and a laser rangefinder
Land Surveying: An Example
What types of surveys might you do here and how might you double check your data?
USGS Control Points Very high accuracy GPS Compare with topographic maps Double check bearing with respect to known features
8