Calculation of Bearing from Angles:

If included angles measured clockwise between survey lines at stations and bearing of any one line are known, bearings of all other lines can be calculated as follows:

Bearing of a line = given bearing of adjacent line + Included angle (measured clockwise) between the lines.

If the sum is more than 360^o, then deduct 360^o to obtain the bearing of the line. The process is explained with the help of following examples.

(a) Let fore bearing of line AB, α and included angle θ between AB and BC are given.

Figure: Bearing from Included Angle

Then back bearing of line AB at B would be

α₁  = 150^o + 180^o = 330^o

Included angle θ = 70^o

Then fore bearing of line BC = 330^o + 70^o = 400^o > 360^o.

∴ Fore bearing of line BC = 400^o - 360^o = 40^o.

(b) Let fore bearing of line BC and included angle θ is given. Included angle θ measured from BC to BA = 70_o measured counterclockwise or will be 360_o - 70_o = 290_o measured clockwise. Hence the back bearing of line AB, i.e. WCB of line AB at B would be 40^o + 290^o = 330^o measured clock wise.