MEASUREMENT OF HORIZONTAL ANGLE BY REITERATION METHOD

Aim: To measure the horizontal angles between the given stations about the instrument station as the vertex by the method of reiteration.

Instruments and Accessories Required:

            Theodolite, Pegs, Arrows,Ranging rod, 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 the plate bubble is brought to the centre of the run.
3. The theodolite is set on the face right mode on the vernier A  and the horizontal circle is initially set at 0°00’00” and the station A is sighted .
4. The upper clamp screw is unclamped and the theodolite is swung to the right and the station B,C,D and A are sighted in sequence and the central vertical cross hair is made to bisect these stations and the horizontal angles on both the vernier A and B are observed and recorded. The observations are closed on the first station A.
5. 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” and the station A is sighted.
6. The upper clamp screw is unclamped and the theodolite is swung to the left and the stations D,C,B and A are sighted in sequence and the central vertical cross hair is made to bisect these stations and the horizontal angles on both the vernier A and B are observed and recorded. The observations are closed on the first station A.
7. The observations are recorded in the field book.
8. The mean values of the horizontal angles on vernier A and B are computed for every sighting and the horizontal included angles are determined as the difference in successive mean values.
9. The average of the two sets of horizontal included angles observed one set each for the two initial settings of vernier A is determined as the result.

Tabulation

Inst at

Sighted to

Horizontal Circle Reading

Included Angle

Average Included Angle

Remarks

Vernier A

Vernier A

Mean

°

‘

“

‘

“

°

‘

“

°

‘

“

°

‘

“

FACE RIGHT

P

A

B

C

D

A

FACE LEFT

P

A

D

C

B

A

Result: The horizontal angles between the given stations about the instrument station as the vertex are determined by the method of reiteration

                                i.            Angle APB =

                              ii.            Angle BPC =

                            iii.            Angle CPD =

                            iv.            Angle DPA =