Aquaculture Engineering

Levelling - Types of spirit levelling

Unit 1- Surveying

Levelling

Types of spirit levelling

Differential levelling
It is the method of direct leveling, the object of which is solely to determine the difference in elevations of two points regardless of the horizontal positions of the points with respect to each other. When the points are apart, it may be necessary to set up the instrument several times. This type of levelling is also known as fly- levelling.

Profile levelling
It is the method of direct levelling, the object of which is to determine the elevations of points at measured intervals along a given line in order to obtain a profile of the surface along that line.

Cross–sectioning
Cross-sectioning or cross–levelling is the process of taking levels on each side of a main line at right angles to that line in order to determine a vertical cross – section of the surface of the ground.

Reciprocal levelling
It is the method of levelling in which the difference in elevation between two points is accurately determined by two sets of reciprocal observation when it is not possible to set up the level between two points.

Precise levelling
It is the levelling in which the degree of precision required is too great, is attained by ordinary methods and in which, therefore special equipment or precautions or both are necessary to eliminate as far as possible all sources of error.