Surveyors Level - Different Methods

The following three methods are mostly found for finding out the variations in elevation:

1. Barometric leveling
2. Trigonometric leveling and
3. Spirit leveling

Barometric leveling: Barometric leveling is based on the perception that variation in elevation among two points is reciprocal to the variation in atmospheric pressures at these points. So, a barometer can be applied and the readings detected at various points would provide a measure of the relevant elevation of those points.

At a specified point, the atmospheric pressure is inconstant in the course of the day, as well in the course of an hour. So, the method is relevantly inappropriate and less utilized in surveying work apart from on reconnaissance or exploratory survey.

Trigonometric Leveling (Indirect Leveling): Trigonometric alias Indirect leveling is the method of leveling in which the elevations of points are measured from the vertical angles and horizontal distances are calculated in the construction site similar to the method applied for working out the length of any side in any triangle from exact trigonometric relations.

In a reformed form it is defined as stadia leveling that is normally found in mapping, both the variation in elevation and the horizontal distance among the points are directly measured from the calculated vertical angles and staff readings.

Also Read: Surveying and Leveling – An exclusive e-book written by N.N. Basak

Spirit Leveling (Direct Leveling): Under this leveling method, the vertical distances relating to a horizontal line (perpendicular to the direction of gravity) should be applied to find out the relative differentiation in elevation among two adjoining points. A horizontal plane of sight tangent to level surface at any point is quickly set up with a spirit level or a level vial.

In spirit leveling, a spirit level and a sighting device (telescope) are amalgamated and vertical distances are calculated by looking on graduated rods which are arranged on the points. The method is also called direct leveling. It is the most accurate method for finding out the elevations. Generally, the engineers mostly utilize this method.