SURVEY STATIONS

 SURVEY STATIONS

Survey stations are the points at the beginning and the end of a chain line. They may also occur at any convenient points on the chain line. Such station may be:

 1.   Main stations.

 2.   Subsidiary stations. And

 3.   Tie stations.

Main Stations.

Which stations taken along the boundary of an area as controlling points are known as ‘main stations’. The lines joining the main stations are called ‘main survey lines’. The main survey lines should cover the whole area to be surveyed. The main stations are denoted by (Reff. Fig. 8.a) with letters A, B, C, D, etc. The chain lines are denoted by (Reff. Fig. 8.b).

Subsidiary Stations.

Which stations are on the main survey lines or any other survey lines are known as “subsidiary station”. These stations are taken to run subsidiary lines for dividing the area into triangles, for checking the accuracy of triangles and for locating interior details. These stations are denoted by (Reff. Fig. 8.c) with letters S1, S2, S3, etc.

Tie Stations.

Tie stations are also subsidiary stations taken on the main survey lines. Lines joining the tie stations are called tie lines. Tie lines are mainly taken to fix the directions of the adjacent sides of the chain survey map. These are also taken to form ‘chain angles’ in chain traversing, when triangulation is not possible. Sometimes tie lines are taken to locate interior details. Tie stations are denoted by (Reff. Fig. 8.d) with letters T1, T2, T3, etc.

Base Line.

The line on which the framework of survey is built is known as the ‘base line’. It is most important line of the survey. The longest of the main survey lines is considered the base line. This line should be taken through fairly level ground, and should be measured very carefully and accurately. The magnetic bearing of base line are taken to fix the north line of the map.

Check Line.

Which line joining the apex points of triangle to some fixed point on its base is known as the ‘check line’. It is taken to check the accuracy of the triangle.