Whole Circle Bearing (WCB) | Concept and Problems | Surveying

The horizontal angle made by the survey line with the magnetic north in the clockwise direction is the whole circle bearing (WCB) of that line. This system is also known as the azimuthal system.

In this system, only the north direction is used as reference meridian as in this system the angles/bearings are measured clockwise from the magnetic north direction.

Whole circle bearing

While aligning a survey line, the bearing is very important. Without knowing the bearing, we can not achieve accurate traverse. The whole circle bearing (WCB) is a basic representation system of bearings. In this article, I will let you know the MUST of this bearing system.

The bearing system is of two types - Whole circle bearing and reduced bearing. First, let us understand what is meant by bearing and meridians.

Bearing and Meridians

• The bearing of a line is the direction with respect to a given meridian.

• Meridian is a fixed reference line and generally, the North-South line is taken as a meridian.

Types of meridian and bearing

The meridians can be of the following types-

1. True Meridian - This meridian line is through true north and south poles, and this remains constant throughout. To find out this line, we need astronomical observations. The bearing with respect to true meridian is known as a true bearing

2. Magnetic Meridian - This meridian line lies in the direction indicated by a freely suspended magnetic needle, and this magnetic North-South line changes with location and time as they are affected by earth’s magnetism. Bearing with respect to magnetic meridian is known as the magnetic bearing.

3. Arbitrary Meridian - Well defined reference object like a tower whose position is not going to change, directions are measured with respect to it and they are known as arbitrary bearings.

Whole Circle Bearing (WCB) / Azimuthal System

Whole circle bearings(WCB) are measured clockwise from north of reference meridian. Some of the important characteristics of this bearing are:

• It varies from 0 degrees to 360 degrees in the clockwise direction.

• The WCB of Magnetic North will be zero degrees; Magentic East will be 90 degrees; Magnetic South will be 180 degrees and Magnetic West will be 270 degrees.

• This bearing system is fundamentally used in the prismatic compass.

Nature of Whole Circle Bearing in Four Quadrants

The whole circle bearing of a survey line can be as less as 0 degree and as more as 360 degrees. This bearing completely depends upon the orientation of the survey line.

• If the survey line lies in the first quadrant(Q1 in the 4 Quadrant Systems) then the Whole Circle Bearing lies between the 0° to 90.

• If it lies between the second quadrant then the Whole Circle Bearing of that survey line lies between 90° to 180°.

• If it lies in the third quadrant then the Whole circle bearing will be between the 180° to 270°.

• And in the fourth quadrant, the Whole Circle Bearing values range between 270° to 360°.

The whole circle bearing can also be reduced to a range of 0 to 90 degrees with the help of reduced bearing. The reduced bearing system lies from 0 degrees to 90 degrees. But in reduced bearing system the direction of the survey line has also to be mentioned.

The whole circle bearing can also be converted to reduced bearing system as per our requirement.

Try this simple question!

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