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THEODOLITE SURVEYING

THEODOLITE SURVEYING. S.N. Nanaware Lecturer Civil Engg. P.C. Polytechnic, Pune. THEODOLITE SURVEYING. 1.

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THEODOLITE SURVEYING

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  1. THEODOLITE SURVEYING S.N. Nanaware Lecturer Civil Engg. P.C. Polytechnic, Pune THEODOLITE SURVEYING 1

  2. So far we have been measuring horizontal angles by using a Compass with respect to meridian, which is less accurate and also it is not possible to measure vertical angles with a Compass. So when the objects are at a considerable distance or situated at a considerable elevation or depression ,it becomes necessary to measure horizontal and vertical angles more precisely. So these measurements are taken by an instrument known as a theodolite. THEODOLITE SURVEYING 2

  3. Uses or Purpose of Theodolite • Measuring horizontal and vertical angles. • Measuring the deflection angles. • Measuring the magnetic bearing. • Locating points on a line. • Prolonging survey lines. • Finding difference of level. • Setting out grades • Ranging curves • Tacheometric Survey THEODOLITE SURVEYING 4

  4. CLASSIFICATION OF THEODOLITES • A. • Transit Theodolite. • Non Transit Theodolite. • B. • i) Vernier Theodolites. • ii) Micrometer Theodolites. THEODOLITE SURVEYING 5

  5. CLASSIFICATION OF THEODOLITES A. Transit Theodolite: A theodolite is called a transit theodolite when its telescope can be transited i.e revolved through a complete revolution about its horizontal axis in the vertical plane. Non-Transit type, the telescope cannot be transited. They are inferior in utility and have now become obsolete. THEODOLITE SURVEYING 6

  6. TRANSIT VERNIER THEODOLITE THEODOLITE SURVEYING THEODOLITE SURVEYING 8

  7. DESCRIPTION OF A TRANSIT VERNIER THEODOLITE A Transit vernier theodolite essentially consist of the following : 1. Levelling Head. 6. T- Frame. 2. Lower Circular Plate. 7. Plumb –bob. 3. Upper Plate. 8. Tripod Stand. 4. Telescope. 5. Vernier Scale. THEODOLITE SURVEYING 11

  8. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. • Centering :- Centering means setting the theodolite exactly over an instrument- station so that its vertical axis lies immediately above the station- mark. It can be done by means of plumb bob suspended from a small hook attached to the vertical axis of the theodolite. • 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. THEODOLITE SURVEYING 12

  9. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 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. THEODOLITE SURVEYING 13

  10. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 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 in the face left position, is known astheface left observation THEODOLITE SURVEYING 14

  11. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 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 in the face right position, is known astheface right observation. THEODOLITE SURVEYING 15

  12. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 6. Changing Face the operation of brining the vertical circle from one side of the observer to the other is known as chaining face. It is done in two steps; Firstly revolve the telescope through 1800 in a vertical plane and then rotate it through 1800 in the horizontal plane i.e first transit the telescope and then swing it through 1800. THEODOLITE SURVEYING 16

  13. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 7. Line of Collimation DIAPHRAGM LINE OF COLLIMATION TELESCOPE It is also known as the line of sight .It is an imaginary line joining the intersection of the cross- hairs of the diaphragm to the optical centre of the object- glass and its continuation. THEODOLITE SURVEYING 17

  14. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 8. Axis of the telescope OBJECT GLASS AXIS OF THE TELESCOPE . TELESCOPE It is an imaginary line joining the optical centre of the object- glass to the centre of eye piece. THEODOLITE SURVEYING 18

  15. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 9. Axis of the Level Tube It is also called the bubble line. It is a straight line tangential to the longitudinal curve of the level tube at the centre of the tube. It is horizontal when the bubble is in the centre. THEODOLITE SURVEYING 19

  16. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 10. Vertical Axis It is the axis about which the telescope can be rotated in the horizontal plane. 11. Horizontal Axis It is the axis about which the telescope can be rotated in the vertical plane. It is also called the trunion axis. THEODOLITE SURVEYING 20

  17. TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE. 12. Telescope normal :- The face left position is known as ‘Telescope normal’ or ‘Telescope direct’ or ‘Bubble up’. 13. Telescope Inverted :- The face right position is known as ‘Telescope Inverted’ or ‘Telescope reversed’ or ‘Bubble down’. 14. Transit station :- A point over which the transit stands and is centered when in use. 15.Transit line :- It is a straight line between two transit stations. THEODOLITE SURVEYING 21

  18. ADJUSTMENT OF A THEODOLITE The adjustments of a theodolite are of two kinds :- 1. Permanent Adjustments. 2. Temporary Adjustments. Temporary Adjustment The adjustments are made at each set up of the instrument before we start the observations with the instrument is known as Temporary adjustment. THEODOLITE SURVEYING 24

  19. TEMPORARY OF A THEODOLITE • Setting the theodolite over the station. • Approximate levelling by tripod stand. • Centering • Levelling • Focussing the eye-piece • Focussing the object glass • Setting the vernier THEODOLITE SURVEYING 25

  20. TEMPORARY OF A THEODOLITE • Setting the theodolite over the station :- The tripod stand is placed over the required station. The theodolite is then fixed on top of the stand by wing nut. • Approximate levelling by tripod stand :- The legs of the tripod are placed well apart and firmly fixed on the ground, then approximate levelling is done using this stand. THEODOLITE SURVEYING 26

  21. TEMPORARY OF A THEODOLITE 3. Centering :- Centering is the process of setting the instrument exactly over a station. At the time of approximate levelling by means of the tripod stand it should be ensured that the plumb bob suspended from the hook under the vertical axis lies approximately over the station peg, then with the help of shifting head, the centering is done accurately. THEODOLITE SURVEYING 27

  22. TEMPORARY OF A THEODOLITE 4. Levelling :- Before starting the levelling operation, all the foot screws are brought to the centre of their run. i) The plate bubble is placed parallel to any pair of foot screws by turning both screws equally inwards or outwards the bubble is brought to the centre. ii) The plate bubble is placed perpendicular to the third screw, then turning the third screw clockwise or anti-clockwise the bubble is brought to the centre. iii) The process is repeated several times, so that the bubble remains in the central position both the directions. THEODOLITE SURVEYING 28

  23. TEMPORARY OF A THEODOLITE 5. Focussing the eye-piece :- The eye-piece is focussed so that the cross-hairs can be seen clearly. To do this, the telescope is directed towards the sky or a piece of water paper is held in front of the object glass, and eye-piece is moved in or out by turning it clockwise or anti-clockwise until the cross-hairs appear distinct and sharp. THEODOLITE SURVEYING 29

  24. TEMPORARY OF A THEODOLITE 6. Focussing the object glass :- This is done to bring a sharp image of the object in the plane of cross-hairs and to eliminate parallax. To do this, the telescope is directed towards the object and focussing screw is turned clockwise or anti-clockwise until the image appears clear and sharp. 7. Setting the vernier :- The vernier A is set to 00 & vernier B to 1800 by turning upper clamp & lower clamp. THEODOLITE SURVEYING 30

  25. Meaurement the reading THEODOLITE SURVEYING 30

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