2. • Digital Theodolite
Theodolite may be defined as the
optical survey instrument that is used
to measure the angles between the
specified points both in the vertical
and horizontal plane.
In other words, theodolite may be
defined as the instrument fitted with a
small telescope that can move freely in
the horizontal and vertical plane to
measure the horizontal and vertical
angles in surveying.
3.
4. • Fundamental Axes of Theodolite
•1. Vertical axis
•2. Horizontal or trunnion axis
•3. Line of collimation
•4. Axis of plate levels
•5. Axis of altitude level
6. • Technical Terms Used in Theodolite
Vertical axis: The axis about which the theodolite rotates in a
horizontal plane.
Horizontal axis: The axis about which the theodolite rotates in a
vertical plane.
Centring: Process of setting up the theodolite exactly over the ground
station point.
Transiting: The process of turning the telescope in the vertical plane.
Swing: Continuous motion of the telescope about the vertical plane.
Face left observation: Vertical circle is on the left at the time of
observation.
Face right observation: Vertical circle is on the right at the time of
observation.
A set: It consists of two horizontal measures, one on the face left and
9. • Component parts of the theodolite
• A theodolite consists of a small telescope that is mounted on it.
The telescope consists of sight on the top of it that is used to
align the target.
• The theodolite also consists of a focusing knob that is used to
make the object clear.
• The telescope of the theodolite is fitted with an eyepiece that the
user looks through to find the target being sighted.
• An objective lens is also fitted on the telescope on the opposite
end of the eyepiece. The objective lens is provided to sight the
object, and also with the help of the mirrors inside the telescope,
allows the object to be magnified.
• The base of the theodolite is threaded for easy mounting on a
tripod.
10. • Applications of Theodolite in Surveying
The major application areas of theodolite can be listed as
follows:
1. Navigation
2. Surveying and its applications
3. Measurement as well as laying out the angles and
straight lines
4. Aligning of walls
5. Formation of Panels
6. Plumbing building corners, columns etc.
7. Tacheometric Surveying
8. Finding the difference in the level
9. Ranging Curves
11. • Uses of Theodolite in Surveying
Some of the uses of theodolite in surveying can be listed as
follows:
1. To determine the vertical and horizontal angles.
2. To determine the difference in elevation between the
points.
3. To locate the points on a line.
4. To prolong or extend the survey lines.
12. • Temporary Adjustment of Theodolite in Surveying
The temporary adjustment of the theodolite mainly includes
a set of operations that are carried out to make it ready for
taking the observations.
13. • Temporary Adjustment of Theodolite in Surveying
1. Setting up:
The first step of the temporary adjustment is the setting up of the theodolite.
It includes the process of fixing the theodolite onto a tripod along with
approximate levelling and centring over the station mark.
2. Centring:
Centring is the process of bringing the vertical axis of the theodolite exactly
over the station mark using a centring plate. The centring plate is also known
as a tribrach.
3. Levelling:
It is the process of levelling the base of the instrument to make the vertical
axis vertical usually with an in-built bubble level.
4. Focusing:
Focusing includes removing parallax error by proper focusing of the objective
and the eye-piece.
14. • Using of a Theodolite in Surveying
The theodolite can be used for reading the observations by following
the below-mentioned steps:
1. First of all the point at which the theodolite is to be set is marked with
a stake or surveyor’s nail. This point acts as the basis for measuring the
angles and the distances.
2. The tripod is then set up over the marked point. The height of the
tripod must be adjusted suitably. The centred hole of the mounting plate
should be over the marked point.
3. The legs of the tripod are driven into the ground using the brackets
present on the side of each leg.
4. The theodolite is then mounted on the tripod. It is done by placing the
theodolite on top of the tripod and screwing it in place with the help of
the mounting knob.
15. • Using of a Theodolite in Surveying
5. The height between the ground and the instrument is then
measured to use as the reference for other stations.
6. The theodolite is then duly adjusted.
7. The vertical plummets by using the knobs are then adjusted to
ensure that the instrument remains over the marked point.
8. The crosshairs are aimed in the main scope at the point to be
measured using the locking knobs present on the side of the
theodolite. The horizontal and the vertical angles are recorded using
the viewing scope found on the theodolite’s side.
