SURVEYING USING THEODOLITE, Essays (university) of Survey Sampling Techniques

Measurement of Direction using Theodolite

The different ways by which the direction of a line is depicted in surveyig are computed either

from horizontal angles or from vertical angles or both. Thus, primary elements of observation

during surveying are the horizontal angles and the vertical angles . These quantities can be

observed directly in the field using theodolite.

Measurement of Horizontal Angle (Figure 22.1)

To represent the direction of a line, the horizontal angle of the line from a reference line is to be

measured. The steps required to be adopted are as follows:

1. Two points one on each of the lines, say P and Q, are to be marked.

tangent screw.

4. At this stage the reading of the vernier B should be 180°.

5. Swing the telescope in the horizontal plane and point it to the left station, say P. Tighten

the lower plate clamp screw, and bisect the signal at P exactly using the lower plate

tangent screw. Record the readings in the form of Table 22.1.

6. Loosen the upper plate main screw and turn the telescope the signal at Q is sighted.

Tighten the upper clamp screw and bisect the ranging pole at Q exactly using the upper

plate tangent screw.

7. Read both the verniers A and B and record the readings. The reading of the vernier A is

the angle POQ. The vernier B gives the value of angle POQ after deducting from it 180°.