Procedure for Tacheometric Surveying

 

Procedure for Tacheometric Surveying:

(1) Set up the instrument over the station selected by the chief of the party and accurately level the instrument with reference to the altitude level.

(2) Set the vernier of the vertical circle to zero. With the altitude level at the centre of its run, measure the height of the instrument (the vertical distance from the top of the peg to the centre of the objective) with a measuring tape accurately.

Alternatively, the height may be found out by keeping the stadia rod first in front of the telescope and reading through the object-glass.

(3) Now, orient the instrument. This is done as follows.

The reference meridian may be the magnetic meridian or the true meridian.

When the reference meridian is a magnetic meridian, set one of the vernier to zero and revolve the telescope about the vertical axis loosening the lower clamp till the compass needle points towards the north.

For orienting the instrument with reference to the true meridian, the true bearing of a reference point or some other station of the traverse with reference to the first station should be known.

Then, set up the vernier to read this bearing and revolve the telescope about the outer axis until the station or the reference object is bisected.

(4) Hold the staff on the benchmark and take the bearing, read the vertical angle and the top, bottom, and axial hair readings, (the line of sight may be horizontal or inclined).

If any benchmark is not nearby the area of traversing, the fly level may be carried out from the available Bench Mark (BM), and a temporary BM may be established near the area.

(5) All the representative points under the command of the instrument station are located by taking the bearings, the vertical angles and the staff reading (to the top, bottom and the axial hairs). These observations are termed as “side shots.”

(6) After all the representative points are located from the first station, take a foresight at the second station and note down the bearings. Vertical angle and the staff readings corresponding to the top, bottom and axial hairs.

(7) Shift the instrument to the second station. Set up, centre and level the instrument and measure the height of the instrument as before.

(8) Take a back a sight to the first station. Also observe the bearings, vertical angle, and the staff reading to the top, bottom and axial hairs.

(9) As each station is sighted twice two Values for the distances and elevations of the stations are obtained which should be within the permissible limits; otherwise, the work should be repeated.