The
approximate shape of the earth can best be defined as
an oblate tri-axial ovaloid. But, most of the civil engineering
works, concern only with a small portion of the earth which seems to be a plane
surface. Thus, based upon the consideration of the shape of the earth,
surveying is broadly divided into two types:
Geodetic
Surveying-
In this branch of surveying, the true shape of the earth is taken into
consideration. This type of surveying is being carried out for highly precise
work and is adopted for surveying of large
area.
Plane-Surveying-
In this method of surveying, the mean surface of the earth is considered to be
a plane surface. This type of survey is applicable for small area (less than
200 square kilometer). Thus for most of the Civil Engineering projects, methods
of plane surveying is valid.
Fundamentals assumptions in Plane Surveying:
All distances and directions
are horizontal;
The direction of the plumb line is same at all points within the
limits of the survey;
All angles (both horizontal and vertical) are plane angles;
Elevations are with reference to a datum.
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