MEASUREMENT OF VERTICAL ANGLE

Aim: To measure the vertical angle between the given stations and the horizontal instrument axis about the instrument station as the vertex.

Instrument and Accessories Required:

            Theodolite, Pegs,Arrows, Tape,etc.

Procedure:

1. The theodolite is mounted on the tripod stand.
2. The theodolite is centered over an arbitrarily selected station P from where the given stations can be sighted without any obstruction and the instrument is levelled using the foot screws and booth the plate bubble and the altitude bubble are brought to the centre of their run.
3. The theodolite is set on the face right mode and the vernier A on the horizontal circle is initially set at 0°00’00” .
4. The line of sight is made horizontal by setting both the vernier C and D on the vertical circle at 0°00’00” .
5. The vertical clamp screw is unclamped and the telescope is raised or lowered in a vertical plane and the given station is sighted and the central horizontal cross hair is made tangential to a specific mark on the given station and the vertical angles on both the vernier C and D are observed.
6. The vernier A is then initially set at 90°00’00” and the same vertical angle is observed by repeating the above procedure.
7. The theodolite is then set on the face left mode and the vernier A on the horizontal circle is initially set at 180°00’00” .
8. The line of sight is made horizontal by setting both the vernier C and D on the circle at 0°00’00” and the vertical angle to the given station is observed by repeating the above procedure.
9. The vernier A is then initially set at 270°00’00” and the same vertical angle is observed by repeating the above procedure.
10. The observations are recorded in the field book.
11. The actual vertical angle which is mean of vertical angles on the verniers C and D is computed for each initial setting of vernier A.
12. The average of the four mean values of the vertical angles observed one each for the four initial setting of vernier A is determined as the result.

Tabulation

Inst Station

Object

Face

Angle

Readings on Vernier

Mean

Mean Angle Observed

Remark

C

D

°

‘

“

°

‘

“

°

‘

“

°

‘

“

P

A

Left

APC

Elevation

Right

APC

P

B

Left

BPC

Depression

Right

BPC

Result: The vertical angle between the given station and the horizontal instrument axis about the instrument station as the vertex is determined

1. Angle APC =
2. Angle BPC =