Surveying is a scientific method which determines the three-dimensional positions and angles of relative points on the surface of the earth. Different types of surveying methods are used in construction which is described below.
Types Of Surveying:
Surveying may be divided into two general categories.
1. Geodetic Surveying and
2. Plane Surveying.
1. Geodetic Surveying:
Geodetic surveying is a particular type of surveying where the curvature of the earth is taken into account. Since the earth has a spherical shape, the line connecting any two points on the earth’s surface is curved or is an arc. Hence it involves spherical trigonometry. In geodetic surveying, large distances and areas are measured and its degree of accuracy is comparatively high.
2. Plane Surveying:
Plane surveying is a specific type of surveying where the surface of the earth is considered as plane and the curvature of the earth is not taken into account. The line connecting any two points is a straight line and the angles of polygons are plane angles. This type of surveying is suitable for small and flat areas, and its degree of accuracy is comparatively low. In America, the limit for treating a surface as a plane is about to 250 km2.
Note: The difference in length between the arc and the subtended chord on the surface of the earth is only about 0.1 m in 18.2 km, 0.3 m in 54.3 km and 0.5 m in 91 km respectively.
Classification Of Surveying:
A. Classification based on the nature of the field:
1. Land Surveying.
2. Marine Surveying.
3. Astronomical Surveying.
Land surveying can be sub-divided into following categories:
Land surveying mainly deals with the natural and artificial features of a country such as hills, rivers, buildings, towns, villages etc.
B. Classification based on the object of the survey:
1. Archaeological survey.
2. Geological Survey.
3. Mine Survey.
4. Military Survey.
C. Classification based on the instruments :
1. Chain Surveying:
Chain surveying is the simplest method of surveying in which the linear measurements are directly taken in the field and the angular measurements are not taken. This type of surveying is used over small and leveled area.
2. Plane Table Surveying:
In plane table surveying the field work and plotting is done using a graphical method. It is mostly adapted for small and medium scale mapping where great accuracy is not required.
3. Compass surveying:
In this surveying, a compass is used to determine the direction of survey lines, and the length of survey lines are measured by a chain or tape.
4. Tacheometric Surveying:
Tacheometric surveying is a method of surveying in which the horizontal and vertical distances of relative points are determined without using any sophisticated instruments such as chain , tape etc.
5. Theodolite Surveying:
In this surveying, a theodolite is used to measure the horizontal and vertical angles.
6. Photographic and Aerial Surveying:
This types of surveying are done by taking photographs from elevated ground stations.