Description

Theodolite :

It is the most precise instrument for the measurement of horizontal and vertical angles. It is popular in various surveying applications.

There are two types of theodolite– transit, and non-transit. non-transit theodolites have become obsolete these days.

Transit theodolite is such theodolite in which the telescope can be revolved by 180° in the vertical plane

Parts of transit theodolite include

1. Telescope
2. Vertical circle
3. Index/Vernier frame
4. Standards/A frame
5. Leveling head
6. Two Spindles
7. Lower/Scale Plate
8. Upper/Vernier Plate
9. Plate levels
10. Tripod
11. Plumb bob
12. Compass
13. Striding level

Temporary adjustments of a theodolite include setting over the station, leveling, and elimination of parallax. Setting up includes centering with a plumb bob and approximate leveling. Leveling up is done by the screw head- it is either three screw head or four screw head. Parallax is eliminated by focusing on the eyepiece as well as the objective.

A theodolite can be used to,

• Measure the magnetic bearing of a line
• Measure direct angles
• Measure deflection angles
• Extend a straight line
• Establish a straight line between two points
• Locating point of intersection between two straight lines
• Setting out a horizontal angle
• Setting out an angle by repetition
• Establish grade
• Measure the difference in elevation
• Setting out curves

Repetition method or Reiteration methods can be employed for setting out horizontal angles to obtain more precise results.