The whole bearing system (WBS) and Quadrantal Bearing system (QBS) are two notations of bearings that are used in compass surveying. The WCB system can be converted to QBS or vice versa by a simple calculation.
Different bearings used in surveying and designation of bearings (WCB and QB system) are briefly explained in the article.
Bearing and Angles
A survey line can be measured with relation to another survey line or with relation to the meridian. The first method gives the angle between the line. The second gives the bearing. Hence, the bearing can be defined as the direction of the line with respect to the given meridian.
There are mainly three types of meridian:
- True meridian
- Magnetic meridian
- Arbitrary meridian
1. True Meridian
A line that passes through a point, with a plane passing through the point and the North-south poles form the true meridian. In other words, it forms the line that passes through the true north and the south poles.
The true bearing of a given line is the horizontal angle made with the true meridian through one of the extremities of the line.
2. Magnetic Meridian
The direction that is shown by a freely suspended and floating balanced magnetic needle is the magnetic meridian. A magnetic compass can be used to determine the magnetic meridian. The magnetic compass used for this purpose must be free from other attractive forces.
The magnetic bearing of a given line is the horizontal angle that it makes with the magnetic meridian that is passing through one of the extremities of the line.
3. Arbitrary Meridian
In certain situations, a convenient direction is established with respect to a permanent or a common mark or a signal in the area, during the survey. These are called arbitrary meridians which helps to determine the relative positions of the survey line.
The horizontal angle made by a line with the arbitrary meridian passing through one of its extremities is called as an arbitrary bearing.
Whole Bearing and Quadrantal Bearing Systems
The common bearing designations used in surveying are:
- Whole Circle Bearing System or Azimuthal System (W.C.B)
- The Quadrantal Bearing or Reduced Bearing System (QB)
1. Whole Circle Bearing System or Azimuthal System (W.C.B)
A WCB bearing method measures angles from the magnetic north or with the south in the clockwise direction as shown in figure-1 below.
Hence, the value of the bearing varies from 0 degrees to 360 degrees. A prismatic compass is graduated by a WCB system. As shown in the figure above, the WCB of AB, AC, AD, and AF are Q1, Q2, Q3, and Q4.
2. The Quadrantal Bearing or Reduced Bearing System (QB)
In the QB system, the bearing angle is measured either from North or South whichever is nearer. This can be measured either in clockwise or anti-clockwise. Here, the quadrant at which the line lies has to be mentioned.
As shown in figure-2, 'B' is the bearing of line AC with the south, which is lying in S-E Quadrant. Hence, it is represented as S B E. The Q.B lines vary from 0 to 90 degrees.
Also Read: Magnetic Compass in Surveying