INTRODUCTION
Chain surveyn;g can be used when the area to be surveyed is comparatively small and is fairly flat. However, when large areas are involved, methods of chain surveying a/one are not sufficient and convenient.
Instruments for the direct measurement of directions
(1) True Meridian. True meridian through a point is the line in which a plane, passing that point and the north and south poles, intersects with surface of the earth. It, this passes through the true north and south. The direction of true meridian through a point can he established by astronomical observations.
True Bearing :- True hearing of a line is the horizontal angle which it makes with the true meridian through one of the extremities of the line. Since the direction of- true meridian through a point remain fixed, the true bearing of a line is a constant quantity.
(2) Magnetic Meridian. Magnetic meridian through a point is the direction shown by a freely floating and balanced magnetic needle free from all other attractive forces. The direction of magnetic meridian can he established with the help of a magnetic compass.
Magnetic Bearing. The magnetic bearing of a line is the horizontal angle which it makes wrth the magnetic meridian. passing through One of the extremities of the line. A magnetic compass is used to measure it.
3) Arbitrary Meridian. Arbitrary meridian is any convenient direction towards a permanent and prominent mark or signal, such as a church spire or top of a chimney. Such meridian are used to determine the relative position of line in small area.
- Surveyor's Compass
- Prismatic Compass
Instrument for measurement of angles
- Sextant
- Theodolite
Traverse Survey:- Traversing is that type of survey in which a number of connected survey line form the framework and the direction and length of the survey line are measured with the help of an angle measuring instrument and tape respectively.
BEARINGS AND ANGLES
The direction of a survey line can either be established (a) with relation to each other, or (b) with relation to any meridian. The first will give the angle between two lines while the second will give the bearing of the line:-
Bearing. Bearing of a line is its direction relative to a given . A meridian is any direction· such as (I) True Meridian (2) Magnetic Meridian (3) Arbitrary Meridian.
(1) True Meridian. True meridian through a point is the line in which a plane, passing that point and the north and south poles, intersects with surface of the earth. It, this passes through the true north and south. The direction of true meridian through a point can he established by astronomical observations.
True Bearing :- True hearing of a line is the horizontal angle which it makes with the true meridian through one of the extremities of the line. Since the direction of- true meridian through a point remain fixed, the true bearing of a line is a constant quantity.
(2) Magnetic Meridian. Magnetic meridian through a point is the direction shown by a freely floating and balanced magnetic needle free from all other attractive forces. The direction of magnetic meridian can he established with the help of a magnetic compass.
Magnetic Bearing. The magnetic bearing of a line is the horizontal angle which it makes wrth the magnetic meridian. passing through One of the extremities of the line. A magnetic compass is used to measure it.
3) Arbitrary Meridian. Arbitrary meridian is any convenient direction towards a permanent and prominent mark or signal, such as a church spire or top of a chimney. Such meridian are used to determine the relative position of line in small area.
Arbitrary Bearing. Arbilrary bearing of a line is horizontal angle which it make with any arbitrary· meridian passtng through one of the extremities. A theodolite or Sextant is used to measure it.
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