Aquaculture Engineering

Compass surveying - Fore bearing and Back bearing

Unit 1- Surveying

Compass surveying

Fore bearing, back bearing, conversion one bearing to other bearing

Fore bearing and Back bearing
The bearing of a line, whether expressed in WCB system or in Q.B system, differs according as the observation is made from one end of the line or from the other. If the bearing of line AB is measured from A towards B, it is known as forward bearing or Fore bearing. If the bearing of the line AB is measured B towards A is known as Backward bearing or back bearing. Since it is measured from backward direction.

Considering W. C .B system, From fig 1 Fore bearing of the line AB is θ, back bearing of line AB = Φ, evidently of Φ= θ +180° and From fig 2 the back bearing of CD is Φ and fore bearing is θ . Hence Φ = θ – 180°. In general it can be stated that 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°.

Consider the Reduced Bearing system. From Fig 3 the fore bearing of the line AB is N θ E and the back bearing of the line is S θ W. Similarly from the fig 4, the fore bearing is of the line CD is S θ W and back bearing is called to N θ E .Thus it can be staled 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 remaining same.