CHAIN SURVEYING

CHAIN SURVEYING

  PRINCIPLE 0F CHAIN SURVEYING

The principle of chain surveying is triangulation must. The area to be surveyed is divided into a number of small triangles which should be well conditioned. In this surveying the sides of the triangles are measured directly on the field by chain or tape, and no angular measurements are taken. Here the tie lines and check lines control the accuracy of work.

  It should be noted that plotting triangles requires no angular measurements to be made, if the three sides are known.


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WELL CONDITIONED AND ILL CONDITIONED TRIANGLES 

When no angle in it is less than 30° or greater than 120° is said well-conditioned triangle (Fig. 7.a). An equilateral triangle is ideal triangle (Fig. 7.b). Well-conditioned triangles are preferred because their apex points are very sharp and can be located by a single ‘dot’. There are no possibility of relative displacement of the plotted point.

  A triangle in which an angle is less than 30° or more than 120° is said to be ill-conditioned (Fig. 7.c). Ill-conditioned triangles are not used in chain surveying because their apex points are not sharp and well defined, which is why a slight displacement of these point may cause considerable error in plotting.

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