Classification of Surveying

What is Surveying:-

Surveying is the art of determining the relative position of different objects on the surface of the earth by measuring the horizontal distance between them, and by preparing a map to any suitable scale. It shows the natural features of a country as well different engineering works such as towns, villages, roads, railways, rivers etc. In this, measurements are taken only in the horizontal plane.

Primary Classification of Surveying :-

Surveying is primarily classified as under:

1. Plane Surveying

2. Geodetic Surveying

1. Plane Surveying :-

As all of us know, shape of the earth is spheroidal. Means, its surface is curved. But in plane surveying, the curvature of the earth is not taken into considerations. It means in this type of surveying earth surface is considered as flat surface. This is because plane surveying is carried out over a small area. In such surveying, a line joining any two point is considered to be straight. The triangle formed by any three points is considered a a plane triangle and the angles of the triangle are assumed to be plane angles. 

Plane surveying is conducted by state agencies like the Irrigation Department, Railway Department for small area of work. Plane surveying is done on an area of less then 250 sqkm.

2. Geodetic Surveying :-

In geodetic surveying, the curvature of the earth is taken into consideration. It is extended over a large area. The line joining any two points is considered as a curved line. The triangle formed by any three points is consider to be spherical and the angles of the triangle are assumed to be spherical angles. Geodetic surveying is conducted by the Survey of India department and is carried out over an area exceeding 250 sqkm.

Secondary Classification of Surveying :-

Some Secondary classification of Surveying are also there based upon its purpose, instrument to be used etc.

1. Classification Based on Purpose :-

a. Topographical Survey :-

It is a survey conducted to obtain data and to make a map indicating inequalities of land surface by measuring elevations and locating the natural and man made features of the earth such as, Rivers, Hill, Buildings, Railway lines, Roads, etc.

b. Engineering Survey :-

These are survey work required before, during and after any engineering works. Before any work is started, large scale topographical maps or plans are required as a basis for design. It is especially used for the design and construction of new routes such as roads, railways. It is also used to calculate the area and volumes of land and data for setting out curves for route alignment.

c. Cadastral Survey:-

These are undertaken to produce plans of property boundaries for legal purposes. These are also known as public land survey.

 d. Hydro-graphic Survey:-

These surveys are conducted on or near the water body, such as lakes, rivers, bays, harbors. Marine surveys are special type of hydrographic surveys, covers a broader area near sea for offshore structures, navigation, tides etc. Hydro-graphic survey consists of locating shore lines, water flow measurements and determination of the shape of the area under the water surface, determination of channel depth, location of locks, sand bars, buoys etc.

e. Astronomic Survey:-

These surveys are conducted for determination of latitudes, longitudes, azimuths, local time etc. at various places on the earth by observing heavenly bodies like the sun or stars. The absolute locations of a point on the earth surface is obtained by astronomic surveys.

f. Geological Survey:-

These surveys are conducted to obtain information about different strata of the earth`s surface for the purpose geological studies. Geological maps are prepared depicting the details of the strata.

2. Classification Based on Instruments Used  :-

Based on the instruments used for survey work it can be classified as follows,

a. Chain Surveying:-

It is the simplest type of surveying in which only linear measurements are taken either with a chain or a tape. No angular measurements are considered.

b. Compass Surveying:-

In compass surveying, horizontal angles are measured with the help of a magnetic compass, in addition to this linear measurements are taken with chain or tape.

c. Levelling:-

In this type of surveying, a levelling instrument is used for determination of relative elevations or levels of various points in the vertical plane.

d. Plane Table Surveys:-

In this type of survey, a map or plan is prepared in the field while viewing the terrain after determining the directions of various lines and measuring the linear distances with a chain or tape. The accuracy of plane table survey is very low so it can be used only at locations where magnetic disturbances are available. Its main advantage is that the measurements and plotting are done simultaneously on the field.

e. Theodolite Surveys:-

In this type of survey horizontal and vertical angles are measured with the help of theodolite. A theodolite is a very precise instrument used for measuring horizontal  and vertical angles.

f. Photogrammetric Surveys:-

Photogrammety is the science of taking measurements with the help of photographs. This survey is mainly used for Topographic mapping of larger area because these are extremely useful for obtaining Topographical details of areas which are difficult to access. Photographs are generally taken from an aeroplane. However, for certain areas suitable sites exist, photographs can be taken from ground based cameras.

 

 g. EDM Surveys:-

Trilateration is a type of triangulation in which all the three sides of each triangle are measured accurately with the help of EDM instruments. Then angles are computed indirectly from the known sides of the triangles. This way all the sides and angles are determined.