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1. Subject: Surveying- I CE-226
Instructor: Engr. Haleema AttaUllah
1
Lecture # 7

2. 2
Theodolite
Because of its various uses, the theodolite is sometimes
known as “Universal Instrument”.

3. 3
Variety of Theodolites

4. 4
Purpose / Use of Theodolite
 The following are the different purpose for which the
theodolite can be used:
• Measuring Horizontal Angle
• Measuring Vertical Angles
• Measuring Deflection Angles
• Measuring Magnetic Bearing
• Ranging curves
• Finding difference of elevation between various points

5. 5
Classification of Theodolite
Video:
https://www.youtube.com/watch?v=MGGM90pSEdQ

8. https://www.youtube.com/watch?v=1qYvBb
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In advanced type of theodolite; An optical plummet is provided for
centering of an instrument.
Plate bubble: use to level the instrument by rotating the foot screws
until bubble in the plate bubble comes at the center.
https://www.youtube.com/watch?v=6yyMZ
SHCbCo&t=181s

9. Reading on a main plate from 0 to
360 degree known as a main scale.
Least count is 20’
Reading on a
vernier plate
from 0 to 20’
known as a
vernier scale.
Least count is
20’’
vernier plate has two vernier scales on opposite sides known as A and
B. Before taking readings, zero reading of vernier scale should concide
zero reading of a main scale.

10. 10
Important Terminology
 Centering
The setting of a theodolite exactly over a station mark is known as
centering.
 Transiting
• The method of turning the telescope about its horizontal axis in
a vertical plane through 180o is termed as transiting. In other
words transiting results in a change in face.
Swinging the telescope
This indicates turning the telescope in a horizontal plane. It is
called “right swing‟ when the telescope is turned clockwise
and “left swing‟ when the telescope is turned anticlockwise.

11. 11
Important Terminology
Face right
This refers to the situation when the vertical circle of the
instrument is on the right of the observer when the reading is
taken.
Face Left
Face left means that the vertical circle of the theodolite is on
the left of the observer at the time of taking reading
Changing face
The operation of bringing the vertical circle from one side of
the observer to the other is known as changing face.
https://www.youtube.com/watch?v=usjYy56hs9w

12. 12
Important Terminology
Axis of Telescope
The axis is an imaginary line passing through the optical centre of
the object glass and the optical centre of the eye-peace.
Vertical Axis
It is the axis of rotation of the telescope in the horizontal plane.
Horizontal Axis
It is the axis of rotation of the telescope in the vertical plane.

13. 13
Important Terminology
Temporary Adjustment
The setting of the theodolite over a station at the time of
taking any observation is called temporary adjustment.
Permanent Adjustment
When the desired relationship between the fundamental
lines of a theodolite is disturbed, then some procedures are
adopted to establish this relationship. This adjustment is
known as permanent adjustment.

16. 16
Direct Method of Measuring
Horizontal Angle by Ordinary method
https://www.youtube.com/watch?v=v7P0yaewxpk

18. 18
Direct Method of Measuring
Horizontal Angle
Repetition Method
 In this method, the angle is added a number of times. The total
is divided by the number of reading to get the angle.
 The angle should be measured clockwise in the face left and
face right positions, with three repetition at each face.
 The final reading of the first observation will be the initial
reading of the second observation, and so on.

19. 19
Direct Method of Measuring
Horizontal Angle
Repetition Method
 Follow the procedure of ordinary method to bisect ranging rods
at A and B. Let say it shows a reading of 30 degree at B.
 Now, tight the upper clamp and loose the lower clamp and
again turn the telescope towards ranging rod at A.
 Now, the reading on scale will remain 30 degree.
 Now bisect ranging rod at B. Say now it shows a value of 60
degree. Again follow the same procedure of bisecting ranging
rods at A and B. say it shows 90 degree. Take the average of
these readings to avoid any error.
 For more accurate work , readings can be checked by changing
the face.
 The mean of the two observation give accurate angle of AOB
shown in figure.

20. 20
Direct Method of Measuring
Horizontal Angle

21. 21
Direct Method of Measuring
Horizontal Angle
Reiteration Method
 This method is suitable when several angles are measured from
a single station.
 In this method all the angle are measured successively and
finally the horizon is closed
• Suppose it is required to measure < AOB, <BOC and <COD and
<DOA from O. The procedure is as follows.

22. 22
Direct Method of Measuring
Horizontal Angle
Reiteration Method
 The theodolite is perfectly centered over O and leveled properly
in the usual manner. Suppose, the observation is taken in the
face left position and the telescope is turned clockwise (right
Swing).
 The verniers are set to their initial readings say 0 or 360 degree.
 The upper clamp is fixed and the lower one is loosened.
 The ranging rod at A is perfectly bisected. Now, the lower clamp
is tightened.
 The upper clamp is loosened, and the ranging rod or object at B
is bisected properly by turning the telescope clockwise. The
reading on the vernier <AOB is noted.

23. 23
Direct Method of Measuring
Horizontal Angle
 Similarly, the object C is bisected properly, and the reading on
the vernier is noted BOC is recorded.
 Follow the same procedure to measure angle COD and DOA.
 The sum of the angles should be 360 degree.
 If error is small, the error is distributed among the angle. If the
discrepancy is large, the observation should be taken again.

24. 24
Direct Method of Measuring
Horizontal Angle
 The face of the instrument is changed. Again the vernier are set
at their initial positions. This time the angles are measured
anticlockwise (left Swing)

25. 25
Measuring Vertical Angle
 The vertical angle is the one between the horizontal line (i.e.line
of collimation) and the inclined line of sight. When it is above
the horizontal line, it is known as the angle of elevation.
 When this angle is below the horizontal line, it is called the
angle of depression.
 Consider Suppose the angle of elevation AOC and that of
depression BOC are to be measured. The following procedure
is adopted.
 The theodolite is set up, centered and leveled properly.
 The plate bubble is brought to the centre with the help of foot
screw. Then the altitude level is brought to the centre by means
of a clip screw.
 The zero of the vernier scale is set with the zero reading of
main scale by unclamping vertical tangent screw, the telescope
is then clamped.
https://www.youtube.com/watch?v=quaZ3rTHrvw

26. 26
Measuring
Vertical Angle
 To measure the angle of elevation, the telescope is raised
slowly to bisect the point A accurately by unclamping vertical
tangent screw. The readings on both the verniers are noted,
and the angle of elevation/ depression is recorded.

27. 27
Measuring
Vertical Angle
 The face of the instrument is changed and the point A is again
bisected. The reading on the vernier are noted. The mean of the
angle of the observed is assumed to be correct angle of
elevation.
 To measure the angle of depression, the telescope is lowered
slowly and observations (face left and face right)
 The mean angle of the observation is taken to be correct angle
of depression.

28. Deflection Angle Traversing by Theodolite
The traversing by the method of deflection angles is chiefly
used in railway, highway, canals etc.

30. Correction: consider (110 deg 6
min) this angle less than 90 deg