Bearing in Surveying

In this post, we are going to discuss about the bearing in surveying and its designation. The direction of a survey line can either be established with relation to each other or with relation to any meridian. The first will give the angle between two while the second will give the bearing of the line.

Bearing in surveying

Bearing of a line is its direction relative to a given meridian. A meridian is any direction such as true meridian, magnetic meridian and arbitrary meridian.

1.True meridian

True meridian through a point is the line in which a plane, thus passes through the true north and south poles, intersects with the surface of the earth. It thus passes through the true north and south. The direction of the true meridian through a point can be established by astronomical observations.

True Bearing: True bearing 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 the true meridian through a point remains fixed, the true bearing of a line is a constant quantity.

2. Magnetic Meridian

The magnetic bearing 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 be established with the help of a magnetic compass.

Magnetic bearing: The magnetic bearing of a line is the horizontal angle which it makes with 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 signals, such as a church spire or top of a chimney. Such meridians are used to determine the relative positions of lines in a small area

Arbitrary bearing: Arbitrary bearing of a line is the horizontal angle which it makes with any arbitrary meridian passing through one of the extremities. A theodolite or sextant is used to measure it. These are the bearings in surveying. Now we are going through designations of bearings.

Designations of bearings( Whole circle bearing system or Azimuthal and Quadrantal Bearing}

The common systems of notation fo bearings in surveying are whole circle bearing system or Azimuthal bearing system and Quadrantal bearing

Whole Circle Bearing and Quadrantal Bearing

1.Whole circle bearing system

In this system, the bearing of a line is measured with magnetic north in a clockwise direction. The value of the bearing thus varies from 0 degrees to 360 degrees. Prismatic compass is graduated in this system

2. Quadrantal bearing system

In this system, the bearing of a line is measured eastward or westward from north or south, whichever is neared. Thus, both north and south are used as reference meridians and the direction can be either clockwise of anticlockwise depending upon the position of the line. In a quadrantal bearing system, the quadrant in which lines lies will have to be mentioned. These bearings are observed by surveyors compass.