Fore Bearing and Back Bearing | Surveying

Bearings measured in the direction of progress of survey are known as fore bearing and bearings measured opposite to the direction of survey are known as back bearing.

Bearing of a line is direction with respect to a given meridian; Meridian is a fixed reference line. While setting out a survey line, the bearing readings are necessary

  • Fore Bearing - Bearing measured in the direction of progress of survey

  • Back Bearing - Bearing measured opposite to the direction of survey 

In the figure below, OA is the survey line to be set out. 
 

  • Fore Bearing (FB) of OA = θ1

  • Back Bearing (BB) of OA = θ2

Fore Bearing to Back Bearing

BB = FB ± 180°

  • Use positive sign of FB < 180°

  • Use negative sign of FB > 180°

In reduced bearing system, the angle remains same for FB and BB; Only the quadrants are opposite. 

Example: What is the BB if FB = 250°

BB = FB - 180° (FB > 180°)

BB = 250° - 180° = 70°

In reduced bearing system, FB = S70°W and BB = N70°E

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