Primary Division Of Surveying:
Introduction to the primary division of surveying:
The earth is an oblate spheroid of revolutions, the length of iiS polar axis _{12,713.800 meters) being somewhat less than that of its equatorial axis (12, 756.750 meters. Thus, the polar axis is shorter than the equatorial axis by 42.95 km.
This is less than 0.34 percent of the Earth’s diameter. If we ignore the iniquities on earth. The imaginary spherical surface is a curved surface, and each aspect of it is normal to the plumb line.
The ejection of such a surface with a plane passing through the center of the earth forms a continuous line around the earth. Part of such a line is called the ‘level line’ and the circle defined by the by is called the ‘Great Circle’.
Thus in Fig. the distance between two points, P and Q is the length 0f the arc of the great circle passing through obese points and is evidently somewhat more than the chord intercepted by the arc.
Consider three points P, Q, and R (Fig.) and three-level lines passing through ti1ese points. The surface within the triangle
PQR so formed is a curved surface and the line forming that’s sides are arcs of great circles. The figure is a spherical triangle.
TI1e angles p, q, and r of the spherical FIG. angle is somewhat more than correspond SURVEYING ing angles p’, q’ and r’ of the plane triangle.
If the points are so far, the difference will be considerable. If the points are near, the difference will be negligible.
Whether the surveyor should consider. Everyone’s surface can be curved or considered, because the plane depends on the character and magnitude of the survey and the accuracy required.
Thus, primarily, surveying can be divided into two classes:
- Plane Surveying
2.Geodetic Surveying
1.Plane Surveying:
The plane survey is a type of survey in which the surface of the earth is considered horizontal and the spherical shape is ignored.
All triangles formed by survey lines are considered to be horizontal triangles.
The level line is considered straight and all plumb lines are to be considered parallel.
Normally, we are concerned with small portions of the earth’s surface and the above assumptions seem to be reasonable in light of the fact that the length of an arc 12 km long lying in the earth’s surface is only 1cm greater than subtended chord and further that the difference between the sum of the angles in a plane triangle and the sum of those in a spherical triangle is only one second for a tringle at the earth’s surface having an area of 195 sq. km.
2.Geodetic Surveying:
The geodetic survey is a type of survey in which the shape of the earth is taken into account.
All lines lying on the surface are curved lines and the tringles are spherical triangles.
It, therefore, involves spherical trigonometry. All geodetic surveys including work of larger magnitude and a high degree of precision.
The purpose of a geodetic survey is to determine the exact position of the Earth’s surface, a system of widely spaced points that form control points and can refer to a low-accuracy survey.
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