Azimuths in Surveying
Azimuths are angles measured from the north or south direction of a meridian. They are measured in degrees, minutes, and seconds. Azimuths are used to locate a line on the surface of the Earth, such as a survey line, in relation to the north direction.
Bearing in Surveying
Bearing is also a horizontal angle measured from the north or south direction of a meridian. It is used to indicate the direction of a line on the surface of the Earth, such as a survey line. Bearings are also measured in degrees, minutes, and seconds.
Comparison of Azimuths and Bearings
Azimuths and bearings are both angles used to represent the direction of a line with respect to a meridian. The main difference between them is that azimuths are used to locate a line on the surface of the Earth, while bearings are used to indicate the direction of a line.
What is Azimuth in Surveying?
What is an Azimuth?
Azimuths are horizontal angles measured from the reference meridian in a clockwise direction. They are also known as Whole Circle Bearings (WCB). Azimuths are used in compass and plane surveying, and are generally measured from the North. However, for astronomers and in the military, azimuths are measured from the South. Azimuths are expressed as values ranging from 0 to 360 degrees.
Types of Azimuths
Azimuths can be classified as geodetic, astronomic, assumed, record or magnetic depending on the meridian used. It is important to state the reference meridian before starting a surveying work to avoid confusion. The forward direction of the line is given by the forward azimuth, while the reverse direction of the line is given by the backward azimuth. The forward azimuth can be converted into back azimuth by adding or subtracting 180 degrees.
Uses of Azimuths
Azimuths are used in boundary, control survey, topographic survey and other types of surveys. For example, if the line AB has an azimuth of ?1= 70 degrees which is the forward azimuth then the backward azimuth is 70+180=250 degrees. Similarly, if the azimuth of the line AD is 230 degrees, then backward azimuth is 230-180=50 degrees.
What is Bearing in Surveying?
What is Bearing?
Bearing is an angle measured between a reference meridian and a given line. The angle is usually less than 360 degrees and is represented by N or S followed by an angle value and E or W direction, e.g. N60E.
Bearing of Line AB:
From the figure-2, the bearing of line AB is less than 90 degrees as it lies in the first quadrant NE.
Types of Bearing:
Bearing can be measured from different types of meridians such as magnetic, grid, assumed, geodetic, and astronomic. Magnetic meridian is obtained by observing the needle of the compass.
Difference between Azimuths and Bearings in Surveying
| SL.No | Azimuths | Bearings |
| 1 | The value varies from 0 to 3600 | The value varies from 0 to 90 degrees |
| 2 | Represented by a numerical value | Represented by two letters and the numerical value |
| 3 | The angles are measured clockwise only | The angles are measured both clockwise and anticlockwise |
| 4 | A single set of measurement is taken either from North or South | The angles can be measured either from north or south for a single survey |
Table.1. Comparison of Bearings and Azimuths in Surveying
Computation of Azimuths and Bearing
Given the quadrant in which the line lies and provided the value of azimuth or bearing can help determine the other value.
| Quadrant | Bearing to Azimuth Conversion |
| I (NE) | Bearing = Azimuth |
| II(SE) | Bearing = 1800 – Azimuth |
| III(SW) | Bearing = Azimuth – 1800 |
| IV (NW) | Bearing = 360 – Azimuth |
Table.1. Conversion of Bearing to Azimuth