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Chapter:
1. Define Trignometric levelling. Write down it's types.
Trignometric levelling is the indirect method of levelling in which the relative elevation of various points are computed from the vertical angles measured with a theodolite and the horizontal distances measured with a tape or computed trignometrically.
It is generally used in topographic work and in very rugged terrain where direct levelling is not possible.It is not accurate as direct levelling.
Trignometric levelling are of two types:
- Plane Trignometric levelling
- Geodatic Trignometric levelling
Plane Trignometric levelling:
It is based on the principle of plane surveying.Here, the distance between the points are assumed to be small so that the effect of either refraction and curvature can be neglected or proper correction may be applied linearly.
Geodatic Trignometric levelling:
It is based on the principle of geodatic surveying.Here, the distance between the points are assumed to be very large so that the correction for curvature and refraction are applied in angular measure directly to the observed angles.