What is Fore Bearing and Back Bearing in Surveying?

Do you know what is fore bearing and back bearing?

In this post, we are going to discuss about the difference between fore bearing and back bearing. The bearing of a line, whether expressed in W.C.B system or in Q.B system, differs according to as the observation is made from one end of the line or from other. If the bearing of a line AB is measured from A towards B, it is known as fore bearing or Fore bearing (F.B).

If the bearing of the line AB is measured from B towards A, it is known as backward bearing or Back bearing (B.B), since it is measured in the backward direction.

Considering first the W.C.B system and referring to the figure below, the back bearing of line AB is Φ. Evidently Φ=180° + θ. Similarly from the second figure, the back bearing of CD is Φ and fore bearing θ, hence  Φ=θ — 180 °. Thus, in general, it can be stated as B.B=F.B ± 180 °, using plus sign when F.B is less than 180° and minus sign when F.B is greater than 180 °.

fore bearing and back bearing

When considering the Q.B system and referring to Fig below the fore bearing of line AB is  NθE and therefore, the back bearing is equal to SθE. Similarly from the next figure, the fore bearing of line CD is SθW and back bearing is equal to NθE. Thus, it can be stated that to convert the fore bearing to back bearing. it is only necessary to change the cardinal points by substituting N for S, and E for W and vice versa, the numerical value of the bearing remains the same

fore bearing and back bearing

These are the difference between fore bearing and back bearing. Thanks for reading.

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