Surveying – Principle and classification of surveying

Definition

In this article, we are going to learn about the basic definition of surveying, Principle of surveying and classification of surveying. Surveying is the art of determining the relative positions of points on, above, or beneath the earth’s surface using direct or indirect measurements of distance, direction, and elevation. The application of surveying requires knowledge of mathematics, physics, and to some extent, astronomy.

The knowledge of surveying is advantageous in every field of engineering such as water supply schemes, irrigation projects, transmission lines, bridges, buildings etc. There are also various classification of surveying based on the field of survey, the object of survey, and the instrument used.

Primary divisions of surveying

Primarily, surveying can be divided into two types,

• Plane surveying
• Geodetic surveying

1) Plane surveying

It is the type of surveying in which the surface of the earth is considered as a flat plane i.e., the curvature of the earth is not considered. All triangles formed by survey lines are considered as plane triangles. The above assumption is reasonable for smaller areas, hence plane surveying can be adopted if the surveying area is less than or equal to 250 km².

2) Geodetic surveying

It is the type of surveying in which the curvature of the earth is taken into an account. All lines lying on the surface are curved lines and the triangles are spherical triangles. It has a higher degree of precision and it can be adopted if the surveying area is greater than 250 Km².

Principles of surveying

The main two fundamental principles of surveying are,

1.Working from whole to part

It is very important to establish the control points at higher precision. Minor control points can be established further from it by less precise methods. And the details are established from minor control points by minor traverse. The idea of working in this way is to prevent the accumulation of minor errors in the end.

2.Location of a point by measurement from two points of reference

To locate the position of a point at least we need two measurements. It may be both linear, 1 linear 1 angular, or both angular measurements.

Classification of surveying

There are several classification of surveying and they are,

1) Based upon the Nature of the field survey

1) Land surveying

a) Topographical surveys

This classification of survey is made to determine the natural features of the country such as rivers, streams, lakes and artificial features such as roads, railways, canals, etc.

b) Cadastral surveys

These surveys are made to fix the boundary line of the property.

c) City surveying

They are made in connection with the construction of streets, water supply systems, sewers and other works.

2) Marine or Hydrographic survey

This classification of survey deals with the water bodies for purpose of navigation, water supply, or for the determination of mean sea level. It also consists of works like measurement of discharge of the streams and observing the fluctuations of an ocean tide.

3) Astronomical survey

This classification of survey enables the surveyor to determine the absolute location of any point and the direction of any line on the surface of the earth. It also consists of observations of heavenly bodies such as the sun or star.

2) Based on the object of the survey

1. Engineering survey – It is undertaken to determine the quantities for engineering works such as roads, sewers, etc.
2. Military survey – Used for determining points of strategic importance.
3. Mine survey – Used for exploring the mineral wealth of the nation.
4. Geological survey – Used for determining different strata in the earth’s crust.
5. Archaeological survey – Used for unearthing antiques.

3) Based on the instruments used

1. Chain survey
2. Theodolite survey
3. Transverse survey
4. Triangulation survey
5. Tacheometric survey
6. Plane table survey
7. Aerial survey
8. Photogrammetric survey