The observation angles are a fundamental component of field surveying. In the determination of a bearing (or azimuth) the angle must be measured from a reference direction- generally north. The reference direction may have been determined in a previous survey, GPS observations or other method.

In the above illustration it can be seen that the ÐAOB is the difference between the bearings of the lines O®B and O®A. Thus to determine O®B the bearing , the bearing O®A must have been known.

Symbols

Ð = subtended angle

® = line between two points.

Calculate angles between bearings.