THEODOLITE SURVEYING
Q. 1. Name the fundamental lines of a transit theodolite. What do you mean by “face left” and “face right” observation?
Answer:
The fundamental lines of a transit theodolite are:
(i) The horizontal axis.
(ii) The vertical axis.
(111) Axis of level tube.
(iv) The line of collimation.
(v) The axis of plate levels. “Face left” means the vertical circle of the theodolite is on the left of the observer at the time of taking readings.
“Face right” means the vertical circle of the theodolite is on the right of the observer at the time of taking readings.
Q.2. A theodolite was set up at distance of 100 m from a chimney and the angle of elevation to its top was 16°42'. The staff on a BM of RL 50.750 with telescope horizontal was 1.250. Find the RL of the top of the chimney.
Answer:
From the above figure (figure 1),
H, = Height of the top of the chimney from the horizontal line passing through the staff reading = 1.250
RL of BM in which staff is held = 50.750
Then, RL of the top of the chimney = (RL of BM + H1 ) + H2
= (50.750 + 1.250 ) + 100 tan 16°42'
52 + 30 = 82 m (ans.)
Q.3. Briefly describe a method of traversing by theodolite. What do you mean by closing error of a closed traverse.
Answer:
Method of traversing a closed traverse with a theodolite:
1. Consider fig 1. The theodolite is set up and centered over A. The plate bubble is leveled. Vernier A is set at 0 ° and vernier B at 180°. The upper clamp is fixed.
2. The telescope is oriented along the north line with the help of the tubular compass fitted to the instrument. Then the magnetic bearing of AB is measured.
3. Again vernier A is set at 0 ° and the upper clamp is kept fixed.
4. The lower clamp is loosened and the ranging rod at E is bisected. Now, the clamp is tightened and the upper one opened. By turning the telescope clockwise, the ranging rod at B is bisected. The readings on the verniers are noted. ZA is obtained by this.
5. Similarly, the other angles are measured by centering the theodolite at B,C,D and E.
6. For plotting the traverse, latitudes and departures of the traverse legs are calculated.
In a closed traverse the algebraic sum of latitudes must be equal to zero and so should the algebraic sum of departures.
But due to the errors in field measurements of angles and lengths, sometimes the finishing point may not coincide with the starting point of a closed traverse as shown in fig 2. The distance by which a traverse fails to close is known as closing error.
Closing error = √(ΣL)²+(ΣD)²,
Where L = latitude and D = Departure.
Q.4
The following angles were measured in a closed traverse ABCD in a clockwise direction :
Station included angle
B 320⁰40'
C 285⁰20'
D 310⁰00'
If the observed bearing of line AB is 40⁰40' . Calculate the bearing of remaining sides .
Answer
Q.5 The following records are obtained in a traverse survey where the length and bearing of the last line were not recorded.
Line Length (m) bearing
PQ 75.50 30⁰24'
QR 180.50 110⁰36'
RS 60.25 210⁰30'
SP --------- --------
Compute the length and bearing of line SP.
ANSWER:
Q.6. What are the essential parts of a transit theodolite?
Answer:
The essential parts of a transit theodolite:
(i) Trivet
(ii) Foot screws
(iii) Tribrach
(iv) Leveling head
(v) Compass
(vi) Telescope
(vii) Attitude bubble
(viii) Plate bubble
(ix) Index bar
(x) Lower plate
(xi) Upper plate
(xii) Spindles
(xiii) Vertical circle
(xiv) A frame
Q7. What is a traverse? What are the different types of traverses?
Answer:
A traverse is a series of connected lines the length of which are measured by chain and the directions of which are fixed by compass or theodolite. There are two types of traverse - open and closed.
Q8. (a) What is a transit theodolite?
(b) What is a 12 cm theodolite?
(c) What are the functions of theodolite?
(d) Describe the location and function of the plate bubble and the altitude bubble?
(e) What is the function of the shifting head?
Answer:
(a) A transit theodolite is a type of theodolite in which the telescope of the instrument can be given a complete revolution about its horizontal axis in a vertical plane.
(b) A 12 cm theodolite indicates the size of the diameter of the graduated horizontal circle of the theodolite,
(c) The functions of a theodolite are:
(i) It measures the horizontal angles, vertical angles and deflection angles.
(ii) It measures the vertical height of an object.
(iii) It measures the magnetic bearings of lines.
(iv) It measures the horizontal distance between points.
(v) It finds the difference of elevation between points:
(vi) Ranging a line:
(d) The plate bubble is fixed over the horizontal graduated circle and its function is to level at the time of measuring the horizontal angle. Again, the altitude bubble is fixed on the top of the vertical vernier scale and is leveled at the time of measuring the vertical angle.
(e) The function of shifting head I to centre the theodolite exactly over the station mark, and it can work within a small range
Q9. Describe briefly the method of measuring vertical angles by thcodolite.
Answer:
Method of measuring vertical angles by theodolite:
Suppose the angle of elevation AOC and that of depression BOC are to be measured. The following procedure is adopted:
(i) The theodolite is set up at O. It is centered and leveled properly. The zeros of the vērniers (generally C and D) are set at the 0°- 0° mark of the vertical circle. The telescope is then clamped.
(ii) The plate bubble is brought to the centre with the help of foot screws. Then the altitude bubble is brought to the centre by means of a clip screw. At this position the line of collimation is exactly horizontal.
(iii) To measure the angle of elevation, the telescope is raised slowly to bisect the point A accurately. The readings on both the verniers are noted and the angle of elevation recorded.
(iv) The face of the instrument is changed and the point A is again bisected. The readings on the verniers are noted. The mean of the angles of the observed is assumed to be the correct angle of elevation.
(v) To measure the angle of depression, the telescope is lowered slowly and the point B is bisected. The readings on the verniers are noted for two observations (face left and face right). The mean angle of the observation is taken to be correct angle of depression
Q10.Describe briefly the different parts of a theodolite. Sketch not necessary. CHAP: Theodolite Surveying
Answer
Different parts of a theodolite:
1. Trivet: A circular plate having a central, treaded hole for fixing the theodolie on the tripod stand by a wing nut. It is also called the base plate.
2. Foot screws: There are meant for leveling the instrument.
3. Tri bach: A triangular plate carrying three foot screws at its ends. 4. Levelling head: The trivet, foot screws and the tribach constitute a body which is known as the leveling head.
5. Spindles: Consists of two spindles are axes - (i) inner (ii) outer. The two spindles are coaxial.
6. Lower-plate: Lower plate is attached to the outer axis, and also known as the scale plate. It is leveled and the scale is graduated from 0° to 360° in a clockwise direction. The size of the theodolite is designated according to the diameter of the lower plate.
7. Upper – plate: It contains the vernier scales A and B. It is attached to the inner axis. Its motion is controlled by the upper clamp screw and the upper tangent screw.
8. Plate - bubble: Two plate bubbles are mounted at right angles to each other or the surface of the vernier plate. The bubbles are meant for leveling the instrument upper at the time of measuring the horizontal.
9. Standard or “A” Frame: Two frames are provided or the upper plate to support the telescope, the vertical circle and the vernier scales. These frames are known as standards or A-frames.
10. The telescope: It is pivoted between the standards at right angles to the horizontal axis. It is provided with a focusing screw, clamping screw and tangent screw.
11. Vertical Circle: Rigidly fixed with the telescope and moves with it. Divided into four quadrants. Each quadrant is graduated from 0 to 90° in opposite directions, with the 'zero' mark at the ends of the horizontal diameter of the vertical circle.
12. Indexs bar on T frame: It is provided on the standard in front of the vertical circle. It carries two verniers (Card D) at the two ends of the horizontal arm.
13. Altitude bubble: Long sensitive bubble tube is provided on the top of index bar. The bubble it contains is known as the altitude bubble. This is brought to the centre by the clip screw at the time of measuring the vertical angle.
14. Compass: Sometimes a circular box compass is mounted or the vernier scale between the standards. In modern theodolites, an adjustable through compass or tubular compass can be fitted with a screw to the standard. The compass is provided for taking the magnetic bearing of a line.
From matrix
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