S. N. PATEL INSTITUTE OF TECHNOLOGY & RESEARCH CENTRE, Umrakh (A Vidyabharti Trust Institution) ESSENTIAL NOTES ON: * Theodolite Surveying * Computation of Area * Setting out of works By: Prof. H. A. Rathod Civil Engineering Department SNPIT & RC, UMRAKH | This work is licensed under the creative commons attribution-noncommercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/ or send a letter to creative commons, PO box 1866, Mountain View, CA 94042, USA. S. N. PATEL INSTITUTE OF TECHNOLOGY & RESEARCH CENTRE, Umrakh (A Vidyabharti Trust Institution) THEODOLITE SURVEYING By: Prof. H. A. Rathod Civil Engineering Department SNPIT & RC, UMRAKH | This work is licensed under the creative commons attribution-noncommercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/ or send a letter to creative commons, PO box 1866, Mountain View, CA 94042, USA. Contents • Definition & Introduction to SURVEYING • Introduction to theodolite • Uses / Purpose of theodolite • Classification of theodolite • Components / Description of theodolite with sketch • Terminologies / Definition • Setting up the theodolite (Temporary Adjustment) • Measuring Horizontal Angle with theodolite i. General Method ii. Repetition Method iii. Reiteration Method • Measuring Vertical Angle with theodolite • Measuring Deflection Angle with theodolite • Measuring Direct Angle with theodolite • Measuring Magnetic Bearing with theodolite • Prolongation of line with theodolite i. Fore sight method ii. Back Sight Method, and iii. Double reversing Method • Errors in theodolite i. Instrumental ii. Personal, and iii. Natural • Theodolite Traversing i. Fast Angle (OR Magnetic Bearing) ii. Loose Needle Method iii. Included Angle Method iv. Direct Angle Method v. Deflection Angle Method • Closing Error • Latitude & Departure • Balancing the Traverse i. Bowditch’s Rule ii. Transit Rule • Gale’s Traverse Table • Omitted Measurements SURVEYING Surveying or land surveying is the technique, profession, and science of determining the terrestrial or three-dimensional position of points and the distances and angles between them. Examine and record the area and features of an area of land so as to construct a map, plan, or description. THEODOLITE SURVEYING The system of surveying in which the angles are measured with the help of a theodolite , is called Theodolite surveying. The Theodolite is a most accurate surveying instrument mainly used for: (Uses of theodolite) . Measuring horizontal and vertical angles. Locating points on a line. Prolonging survey lines. Finding difference of level. Establishing grades. Setting out curves. Measure height & depths. Measure distance. Alignment of various civil works. Measure slope. & etc. CLASSIFICATION OF THEODOLITES Theodolites may be classified as ; A. Based on movement of telescope: i) Transit Theodolite ii) Non Transit Theodolite • Transit Theodolite • Non-Transit type • The telescope can be transited • The telescope cannot be i.e. revolved through a transited. ○ complete revolution (180 ) • The position of theodolite can about its horizontal axis in the not be changed from face left vertical plane. to face right. • The position of theodolite can • Ranging of line can not be be changed from face left to done by back sighting. face right. • Deflection angles can not be • Ranging of line can be done by measured easily. back sighting. • These are now become • Deflection angles can be obsolete. measured easily. • These are widely used in surveying. B. Based on arrangement to measure angles: i) Vernier Theodolite ii) Micrometer Theodolite iii) Electronic Theodolite Vernier Theodolite: For reading the graduated circle if Vernier are used, the theodolite is called as a Vernier Theodolite. It can measure an angle up-to 20”. This theodolites are commonly used. Micrometer Theodolite: If Micrometer is provided to read the graduated circle then it is called as a Micrometer Theodolite. It can measure an angle up-to 1”. Electronic Theodolite: In Electronic Theodolite, the readings of angle is obtained in digital form. When EDM instrument is attached with Electronic Theodolite it becomes Total Station. SIZE OF THEODOLITE . A theodolite is designated by diameter of the graduated circle on the lower plate. The common sizes are 8cm to 12 cm while 14 cm to 25 cm instrument are used for triangulation work. Greater accuracy is achieved with larger theodolites as they have bigger graduated circle with larger divisions hence used where the survey works require high degree of accuracy. TYPE OF THEODOLITE TRANSIT VERNIER THEODOLITE DESCRIPTION OF TRANSIT VERNIER THEODOLITE Transit vernier theodolite essentially consist of the following essential parts: • Telescope • Vertical circle • A-Frame • Levelling Head • Two spindles OR Axes • Lower Circular Plate • Upper Plate • Upper & Lower clamp screw • Upper & Lower tangential screw • Plumb –bob • Tripod Stand • Vernier Scale • Shifting head • Clip screw • Level tubes OR Plate levels • Altitude level tube FUNDAMENTAL AXES OF THEODOLITE & THEIR RELATIONSHIP FUNDAMENTAL AXES / LINES OF THEODOLITE : 1. Vertical axis 2. Horizontal axis OR trunion axis 3. Line of collimation OR Line of sight 4. Axis of plate level 5. Axis of altitude level THEIR RELATIONSHIP a. The axis of the plate level must lie in a plane perpendicular to the vertical axis. b. The line of collimation must be perpendicular to the horizontal axis. Vertical axis, Horizontal axis and Line of collimation must intersect at a point. c. The Horizontal axis must be perpendicular to the Vertical axis. d. The Axis of altitude level must be parallel to the line of collimation. TERMS USED IN TRANSIT VERNIER THEODOLITE 1. Centering: Centering means setting the theodolite exactly over an instrument station so that its vertical axis lies immediately above the station mark. 2. Transiting: Transiting is also known as plunging or reversing. It is the process of turning the telescope about its horizontal axis through 1800 in the vertical plane. 3. Swinging the telescope: It means turning the telescope about its vertical axis in the horizontal plane. A swing is called right or left according as the telescope is rotated clockwise or counter clockwise. 4. Face Left: If the vertical circle of the instrument is on the left side of the observer while taking a reading ,the position is called the face left; and the observation taken on the horizontal or vertical circle in this position, is known as the face left observation. 5. Face Right: If the vertical circle of the instrument is on the right side of the observer while taking a reading ,the position is called the face right; and the observation taken on the horizontal or vertical circle in this position, is known as the face right observation. 6. Changing Face: It is the operation of bringing the vertical circle to the right of the observer ,if originally it is to the left , and vice – versa. 7. Axis of the Level Tube / Bubble Line: It is a straight line tangential to the longitudinal curve of the level tube at the center of the tube. It is horizontal when the bubble is in the center. 8. Vertical Axis: It is the axis about which the telescope can be rotated in the horizontal plane. 9. Horizontal Axis / Trunnion Axis: It is the axis about which the telescope can be rotated in the vertical plane. 10. Line of Collimation (LOC) / Line Of Sight (LOS): It is an imaginary line joining the intersection of the cross- hairs of the diaphragm to the optical center of the object- glass and its continuation. DIAPHRAGM LINE OF COLLIMATION TELESCOPE 11. Axis Of The Telescope: It is also known an imaginary line joining the optical center of the object- glass to the center of eye piece. OBJECT GLASS AXIS OF THE TELESCOPE . TELESCOPE ADJUSTMENT OF A THEODOLITE The adjustments of a theodolite are of two kinds :- 1. Permanent Adjustments. 2. Temporary Adjustments. 1) Permanent adjustments: The permanent adjustments are made to establish the relationship between the fundamental lines of the theodolite and , once made , they last for a long time. They are essential for the accuracy of observations. 1) Permanent adjustments: The permanent adjustments are made to establish the relationship between the fundamental lines of the theodolite and , once made , they last for a long time. They are essential for the accuracy of observations. The permanent adjustments in case of a transit theodolites are :- . Adjustment of Horizontal Plate Levels. The axis of the plate levels must be perpendicular to the vertical axis. Horizontal axis adjustment. The horizontal axis must be perpendicular to the vertical axis. Collimation Adjustment. The line of collimation should coincide with the axis of the telescope and the axis of the objective slide and should be at right angles to the horizontal axis. Adjustment of Telescope Level or the Altitude Level Plate Levels. The axis of the telescope levels or the altitude level must be parallel to the line of collimation. Vertical Circle Index Adjustment. The vertical circle vernier must read zero when the line of collimation is horizontal. 2) Temporary Adjustment The temporary adjustments are made at each set up of the instrument before we start taking observations with the instrument. There are three temporary adjustments of a theodolite:- i) Setting up and Centering ii) Levelling iii) Elimination of parallax MEASUREMENT OF HORIZONTAL ANGLES: There are three methods of measuring horizontal angles:- i) Ordinary Method. ii) Repetition Method. iii) Reiteration Method. 1. Ordinary Method: To measure horizontal angle AOB:- A B 1. Set up the theodolite at station point O and level it accurately. 2. Set the vernier A to the zero of the horizontal circle. Tighten the upper clamp. 3. Loosen the lower clamp. Turn the instrument and direct the telescope towards A to bisect it accurately with the use of tangent screw. After o bisecting accurately check the reading which HORIZONTAL ANGLE must still read zero. Read the vernier B and AOB record both the readings. 4. Loosen the upper clamp and turn the telescope clockwise until line of sight bisects point B on the right hand side.