Surveying is the art of making suitable measurements in horizontal or vertical planes. This is one of the important subjects of civil engineering. Without taking a survey of the plot where the construction is to be carried out, the work cannot begin.
Levelling is the art of representing relative positions in the vertical plane of different points on the earth’s surface.
It helps in determining the areas that are to be levelled to achieve a certain slope.
Principles of Surveying
All the surveys that are conducted are based on two fundamental principles. They are as follows:
- Working from whole to part
- Fixing a point with reference to two fixed points
Working from whole to part
In order to localize errors and prevent their accumulation, a set of control points is always established with great precision first for the whole area to be surveyed.
Later on, details or filled in between these control points to a relatively smaller precision.
This fundamental work principle is known as “Working from whole to part”.
Fixing a point with reference to two fixed points
Survey stations are fixed by atleast two measurements, either both linear or angular measurements or linear and angular measurements from two control points.
Let A and B be two control points. Another point C can be located by any of the following methods:
By two distances AC and BC
The point C is plotted by intersection of arc taking AC and BC as radius and with centres A and B.
By perpendicular distance CD and distance AD
By angle <CAB and distance AC
By the angles BAC and ABC
By the <ABC and distance AC
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