Surveying

Keywords: Levelling, principle, differential levelling, station, backsight, foresight, intermediate sight, change point, turning point, balancing

Let’s now move on to the basic principle of levelling. If you want to refresh the basic concepts of levelling, you can read them here.

Simple levelling
When the levelling instrument is properly leveled, the bubble tube axis and the line of sight will be horizontal and the vertical axis of the instrument will be vertical. The bubble must be central and traverse. The line of sight will remain in a horizontal plane when the telescope is rotated. Thus if the telescope is sighted towards a staff kept on a point of known elevation, the height or elevation of the line of sight can be determined. If the telescope is now directed to staff kept on points of unknown elevation, the staff readings can be read. From which the reduced levels of the unknown points can be determined.

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Keywords: Levelling, dumpy level, level, levelling staff, telescope

In the previous articles we have seen that what is levelling and what are the major types of levelling employed in different circumstances. Let’s move on to the next topic in this section, which is levelling instruments and accessories.

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Keywords: Levelling, Direct levelling, Trigonometric levelling, Barometric levelling, Hypsometric levelling, Simple levelling, Differential levelling/Compound levelling, Check levelling, Profile levelling, Cross-section levelling, Precise levelling, Reciprocal levelling

We have already discussed what is mean by levelling and which are the main terminologies used in the levelling. If you want to refresh this concept, you can read them here.
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Keywords: Levelling, Surveying, Dumpy level, benchmark, Mean Sea Level, M.S.L, Elevation, G.T.S benchmarks, arbitrary benchmarks, datum, Bombay port, Reduced level, Survey of India

What is Levelling?
Levelling is defined as the process of determining the relative heights or elevations of points or objects on the earth’s surface. The elevation of a point is defined as its vertical distance measured above or below a reference level which is called datum. The most widely used datum surface is the Mean Sea Level, M.S.L

Levelling instrument: Dumpy level (Source: Wikimedia Commons)

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Contouring is the science of representing the vertical dimension of the terrain on a two dimensional map. We can understand contouring by considering a simple example.

Let us assume that a right circular cone of base 5m diameter and vertical height 5m is standing upright on its base. Let the base be resting on a horizontal plane at zero level as shown in Figure 1.

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