Reduced Bearing (RB) / Quadrantal Bearing (QB) | Surveying

In Quadrantal bearing (QB) / Reduced bearing (RB) - Bearings are measured either clockwise/anti-clockwise from north/south whichever is close to the line.

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

  • Bearing of line : ​Direction with respect to a given meridian 

  • Meridian is a fixed reference line

Types of meridian and bearing

True Meridian - Line through true north and south poles, and this remains constant throughout. To find out this line, we need astronomical observations.

  • Bearing with respect to true meridian is known as true bearing

Magnetic Meridian - Direction indicated by freely suspended magnetic needle, and this magnetic N-S line changes with location and time as they are affected by earth’s magnetism.

 

  • Bearing with respect to magnetic meridian is known as  magnetic bearing.


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

Reduced Bearing (RB) / Quadrantal Bearing (QB)

Bearings are measured either clockwise/anti-clockwise from north/south whichever is close to the line.

  • Angles vary from 0 degrees to 90 degrees

  • It is measured from either clockwise/anti-clockwise from north/south (If the line is closer to south and going towards west, it is read as Sβ°W)

  • Four quadrants are possible namely NE, SE, SW and NW 

  • Surveyor's compass used RB system

In the figure below, the line lies closer to south line (and towards west) - in the third quadrant. 

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