Surveying
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
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