Plane and Applied Surveying -2 Theodolite Theoretical part -1 Prepared by Asst. Prof. Salar K. Hussein Asst. Lecturer Mr. Kamal Yaseen Overview v Introduction About Theodolite Instrument v Theodolite and its classification v Parts of Theodolite v Theodolite Axis and conditions v Setting up the Theodolite v Levelling & Centring - the Theodolite v Readings in the Theodolite v Theodolite – Instrument Checks v Sources of errors Erbil Polytechnic University Technical Engineering College Civil Engineering Department

1. Plane and Applied Surveying -2
Theodolite Theoretical part -1
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Prepared by
Asst. Prof. Salar K. Hussein
Asst. Lecturer Mr. Kamal Yaseen
Technical Engineering College
Civil Engineering Department

2. Overview
v Introduction About Theodolite Instrument
v Theodolite and its classification
v Parts of Theodolite
v Theodolite Axis and conditions
v Setting up the Theodolite
v Levelling & Centring - the Theodolite
v Readings in the Theodolite
v Theodolite – Instrument Checks
v Sources of errors
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3. Introduction About Theodolite Instrument
theodolite is a precise Surveying instrument used for
measuring angles both (horizontally and vertically). Theodolite
can rotate along their horizontal axis as well as their vertical
axis.
. Theodolites can also be used to mark out straight and curved
lines in the field. Determining the difference in elevation,
setting out curves… etc.
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4. The following are the different purposes for which the
theodolite can be used:
1- Measuring horizontal angles.
2- Measuring Vertical angles.
3- Measuring deflection angles.
4- Measuring magnetic bearing.
5- Measuring the horizontal distance between two points.
6- Finding the vertical height of an object.
7- Finding the difference in elevation between various points.
8- Ranging a line.
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5. Parts of a Theodolite
1 - Tripod
It should be of a rigid type capable of fixing the position of the instrument with a small
lateral movement on its top when required.
2 - Foot screws
These are provided for leveling the instruments.
3 - Plate level
Provided for checking the level of the instrument.
4 - Horizontal clamp
Provided to clamp the movement in horizontal plane.
5 - Vertical clamp
For clamping movement in vertical plane.
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6. 6 - Telescope
In a telescope vertical hair is used for horizontal angle measurement while horizontal hair is
used for vertical angle measurement. Focusing arrangement for the object glass is usually
provided in the body of the telescope. Collimator is provided to bring the object in the field
of view.
7 - Vertical axis
It is the axis around which the telescope rotates in horizontal plane.
8 - Horizontal axis
It is the axis around which telescope rotates in vertical plane.
9 - Angle reading arrangement
In screen display you can note angle measurements taken with Theodolite
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7. 10 - Optical plummet
It is provided for centering the instrument over a ground station.
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Optical plummet

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9. Theodolite Axis
1- V-V axis (Vertical axis or Rotation axis).
2- L-L axis (Plate Bubble axis).
3- Z-Z axis (Line of Sight axis).
4- H-H axis (Transit axis).
5- P.V.C. (Plan of Vertical Circle).
6- P.H.C. (Plan of Horizontal Circle).
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10. Components of theodolite
Trivet
vIt is a circular plate having a central, threaded hole for fixing the theodolite
on the tripod
vTribrach
It is a triangular plate carrying three foot screws at its ends.
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Trivet
Tribrach

11. Components of theodolite
Screws:
A theodolite instrument has number of screws as its component parts. These
are classified into different types depending on their functions.
Levelling Screws (Crosshairs by Theodolite)
Clamp Screws
Tangent Screws
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12. Components of theodolite
Leveling Screws:
These are present in the leveling head of a theodolite in between trivet and tribrach.
These screws are used for leveling the instrument; to make plate level axis
horizontal.
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Levelling screws

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14. 14

15. Hold Theodolite by its handle
Attach to tripod head
Do not leave the handle until the theodolite
is attached to the tripod

16. Temporary Adjustment
Temporary Adjustment
At each station point, before taking any observation, it is required to carry out some
operations in sequence. The set of operations those are required to be done on an
instrument in order to make it ready for taking observation is known as temporary
adjustment.
Temporary adjustment of a Vernier theodolite consists of following operations:
Ø Setting out,
Ø Centring,
Ø Levelling
Ø Focussing.
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17. Temporary Adjustment
Setting out
1-Before removing the theodolite from its box, it should be guaranteed that
• The tripod head is approximately level
• The tripod legs are firmly fixed in the ground
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18. Temporary Adjustment
Centring:
The operation involved in placing the vertical axis of the instrument exactly over
the station mark is known as centring.
1-The approximate centring of the
instrument is done by moving the
tripod legs radially.
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19. Temporary Adjustment
2. Next Place the instrument on the tripod head. Supporting
it with one hand, the centering screw on the bottom of the
unit to make sure it is secured to the tripod.
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20. Temporary Adjustment
3-Looking through the optical plummet eyepiece, turn the optical plummet eyepiece
to focus on the reticle.
Turn the optical plummet focussing ring to focus on the survey point
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21. Temporary Adjustment
Levelling
Levelling of an instrument is done to make the vertical axis of the instrument truly vertical. Generally,
there are three levelling screws and two plate levels are present in a theodolite instrument.
Step 1: Bring one of the level tube parallel to any two of the foot screws, by rotating the upper part of
the instrument.
Step 2: The bubble is brought to the centre of the
level tube by rotating both the foot screws either
inward or outward. The bubble moves in the same
direction as the left thumb.
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22. Temporary Adjustment
Step 3: The bubble of the other level tube is then brought to the centre of the level
tube by rotating the third foot screw either inward or outward. [In step 1 itself, the
other plate level will be parallel to the line joining the third foot screw and the centre
of the line joining the previous two foot screws.]
Step 4: Repeat Step 2 and step 3
in the same quadrant till both the
bubble remain central.
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23. Temporary Adjustment
Step 5: By rotating the upper part of the instrument through 180°, the level tube is
brought parallel to first two foot screws in reverse order. The bubble will remain in the
centre if the instrument is in permanent adjustment.
Otherwise, repeat the whole process starting from step1 to step5.
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24. 24

25. Position a
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26. 26

27. Temporary Adjustment
Focusing
To obtain the clear reading, the image formed by the objective lens should fall in the plane of
diaphragm and the focus of eye-piece should also be at the plane of diaphragm.
Thus, focusing operation involves two steps:
ØFocusing of the eye-piece lens.
ØFocusing of the objective lens.
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28. 2 - Permanent Adjustments
These are to be tested after a long interval or at the beginning of an important
project. The field party is only expected to carry out the test and adjustment, if
required will be done by the trained for this purpose in a workshop.
Permanent Adjustments for a theodolite .
First adjustment: - to make the axis of the plate levels perpendicular to the vertical
axis
Second adjustment: - to make the line collimation agree with the optical axis of the
telescope
Adjustment of Horizontal Hair:-
Adjustment of Vertical Hair:-
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29. Permanent Adjustments
Third adjustment:-
To make the horizontal axis perpendicular to the vertical axis
Forth adjustment:-
To make the bubble – tube axis of the telescope parallel to the line of collimation ,
to test this adjustment , the two – peg test
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30. Definitions
Face left:
Face left observation while taking the reading if the vertical circle is towards the left of the observer, it is
called face left observation.
Face Right:
Face right observation – while taking
readings if the vertical circle is towards the
right of the observer then it is called face
right observation (this condition is also
called telescope inverted condition)
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31. Sources of errors
1- Personal errors
2- Instrumental errors
3- Natural of errors
1- Personal errors :
Errors which result from the possibility of the observer the same for every observer the
potential of audio-visual and sensory and non-perfect in these senses cause this type of
errors
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32. 2- Instrumental errors: The errors resulting from devices used in the monitoring result of
not making devices and measuring instruments up to the degree of perfection.
3-Natural of errors:
The errors that a rise as a result of continuing changes in the factors of
1-wind
2- air temperature
3- pressure.
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