•  CLASSIFICATION OF SURVEY

                                                            An attempt has been made here to group the types of survey. However, it is not that significant or satisfactory as there are differences in objectives and dissimilarities in the procedures employed to distinguish between them.

  •  Based on Accuracy Desired
  • Plane survey- Survey in which the mean surface of earth is regarded as plane surface and not curved as it really is, is known as plane surveying. The following assumptions are made:

(a) A level line is considered a straight line and thus the plumb line at a point is parallel to the plumb line at any other point.

(b) The angle between two such lines that intersect is a plane angle and not a spherical angle.

(c) The meridians through any two points are parallel.

      When we deal with only a small portion of earth's surface, the above assumptions can be justified. The error introduced for a length of an arc of 18.5 km is only 0.0152 m greater than the subtended chord and the difference between the sum of the angles of spherical triangle and that of plane triangle is only one second at the earth's mean surface for an area of 195.5 km². Therefore, for the limits of the provisions stated above, the survey may be regarded as a plane survey.

        Plane surveys are done for engineering projects on large scale such as factories, bridges, dams, location and construction of canals, highways, railways, etc., and also for establishing boundaries.

  • Geodetic survey- Survey in which the shape (curvature) of the earth's surface is taken into account and a higher degree of precision is exercised in linear and angular measurements is termed as geodetic surveying. Such surveys extend over large areas. The measurements must be made to the highest possible standard.

       A line connecting two points is regarded as an arc. The distance between two points is corrected for the curvature and is then plotted on the plan. The angles between the intersecting lines are spherical angles. All this necessitates elaborate field work and considerable mathematical computations.

      The geodetic surveying deals in fixing widely spaced control points, which may afterwards be used as necessary control points for fixing minor control points for plane survey. This is carried out by the Department of National Survey of India.


 

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