PRINCIPLE OF TRIANGULATION

• In triangulation, the whole area under consideration is covered with a framework of triangles. It is based on the principle that:
  “If the length and direction of one side and all the three angles of the triangle are measured precisely then the lengths and directions of the remaining two sides can be determined. The precisely measured first line is called as base line.”
• Furthermore, the other two sides of the triangle (whose lengths and directions are now known) act as base lines of the other interconnected triangles. This process goes on further which gives rise to a network of triangles throughout the area to be surveyed.
• Check base: When the whole area has been covered with triangles, then at last, as a check, the length of one of the sides of the last triangle is also measured directly and compared with the computed This side is called as check base.

Note:

This traditional method of triangulation in which the base lines and the check base are measured by invar tapes has now become out of vogue. Now we have more advanced methods like EDM which not only measures the base line but, now we can have more check bases in the network.

Scale error: The difference between measured and computed check bases is called as scale error.

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