Surveying

Introduction
A dumpy level, also known as an automatic level or builder’s level, is a tool used to determine the elevation of landmasses. Though they may appear intimidating or confusing, dumpy levels are relatively simple to use once you understand how to set them up and what types of measurements they provide.

Dumpy levels are also known as builder levels, Y levels, and so on. Willian Gravatt invented it in 1832. The dumpy level’s operation establishes the relationship between two or more points on a horizontal surface using an inbuilt telescope and a bubble level. The primary advantage of using the Dumpy level over other leveling instruments is its greater accuracy. For most Tacheometric methods, a dumpy level is known for high precision values. A dumpy level’s accuracy can be as high as 1:4000 for every 100 meters.
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Keywords: Levelling, precautions, errors in leveling

Since you have acquired a good understanding about leveling, let’s now move on to the last topic in this section.

Levelling has to be done with utmost care to obtain accurate and precise readings. Any error in the readings could possibly harm all the calculation and subsequent surveying processes.

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Keywords: Levelling, difficulties in levelling, errors in levelling

The last two topics in leveling are the difficulties and precautions to be taken for an error-free levelling process. Let’s jump into the first section, difficulties in levelling.

Some of the difficulties that are commonly encountered in levelling are:

When the staff station is more than 3metres above the line of sight
Solution: Measure the distance (d) from line of sight to the staff placed at the station accurately with a tape.
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Keywords: Levelling examples, levelling, rise and fall method, missing entries problem

Since we have already studied about levelling, now let’s move on to a specific problem in this section. The problem of missing entries in the field book is an application level problem, often asked in question papers. An example on this type of problem is illustrated as follows:

Problem: The following level readings have been taken from a page of a level book. Some of the readings are missing. It is required to fill all the entries in the page. Fill up the missing readings and apply the arithmetic checks.
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Keywords: Levelling, reduction of levels, rise and fall methods, height of instrument

In the previous posts we have learned about the leveling, its principles and methods. Now we can move on to a practical illustration of this leveling process.

A level filed book or a level book is used for booking and reducing the levels of various points in a systematic way. There are two methods for reducing the levels namely

• The height of the instrument method
• The rise and fall method

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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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