Surveying is the art of determining the relative position of points on above or beneath the surface of the earth by means of direct or indirect measurements of distances, direction and elevation.
object of surveying
The primary object of a survey is the preparation of a plan map. the results of surveys when plotted and drawn on paper, constitute a plan. Therefore a plan is a representation of the ground and the objects upon it some scale as projected on a horizontal plane. If the scale is large, then it is called a plan. if the scale is small, then it is called a map. Example: a plan of a building, a map of India.
Purposes of survey
Following are some of the purposes of survey:
ü To prepare archeological maps, geological maps, military maps etc.
ü To establish boundary points of properties with reference to the available records and demarcate ownership.
ü To measure quantities in cutting or in embankments using contour maps.
ü To lay out th alignment of engineering structures such as roads, railways etc.
ü To plot profile of a structure(eg. irrigation canal) for ascertaining the carrying capacity of canal, capacity of reservoir etc
ü To determine the relative position of desired points with reference to a known bench mark (eg. position of hill stations with reference to mean sea level).
ü To measure distance between various points (eg. distance between two cities).
Primary divisions of surveying
Survey may be primarily divided into following two divisions.
ü Plane surveying: in plane surveying, the mean surface of the earth is considered as a plane and the spheroid shape is neglected as the surveys extend over small areas.
ü Geodetic surveying: in geodetic surveying, the curvature of earth is taken into account and all lying in the surface are curved lines and the triangles are spherical triangles, since large distances and areas are covered.
Principle of surveying
All surveys are based on two fundamental principles they are:
ü Working from whole to part: in order to prevent accumulation of errors and to localize the minor errors, a set of primary central points are established first with higher precision in and around the area to be surveyed. Later on, in between those primary control points, inner control points are established with less precision method. The details are surveyed with the help of these inner control points, adopting any one method of surveying. This principles is known as working from whole to part.
ü Fixing a point with reference to two fixed points: suppose points 'A'and'B'are known on the distance between them is measured
ü . Let it be required to locate or mark a point 'C'. The relative position of the point C is located with reference to the two fixed points A and B by one of the following methods.
a) Liner measurement
b) Angular measurement
c) Both liner and angular measurements