BEARING AND ITS DIFFERENT PARTS    

 BEARING// TRUE BEARING AND MAGNETIC BEARING// WHOLE CIRCLE BEARING AND REDUCE BEARING 

 BEARING: A bearing is a method of indicating direction. It is the angle, measured in a clockwise direction, between North and a line joining two known points .

Types of Bearing 

As there are three different kinds of north points, there are three kinds of bearings, according to the north point from which they have been measured: 

A Magnetic bearing is one taken with a compass. (An accurate compass needle always points to magnetic north.) 

A Grid bearing is one measured on the map with the compass used as a protractor. 

A True bearing cannot be measured direct, but must be calculated from one of the other two. However, this can be ignored for practical map reading purposes. 

TRUE BEARING : 

True bearing and magnetic bearing in geography generally refer to true north and magnetic north. True north is the direction pointing to the North Pole. On the map, true north is represented by meridians or lines of longitudes.

MAGNETIC BEARING

 Magnetic north is the direction which points to the magnetic pole. Magnetic attraction in the earth 's core causes the needle of a compass to be pulled away from true north.

Calculate True Bearing From Magnetic Bearing

If the magnetic declination at a place at the time of observation is known, the true bearing of a line can be calculated from its magnetic bearing and vice-versa.

Determination of True Bearing From Magnetic Bearing Rules

The following rules are applied to determine the true bearing if the magnetic declination is known:

1. If Declination is East

True Bearing(T.B) = [Magnetic Bearing(M.B) + Declination]

2. If Declination is West

True Bearing = [Magnetic Bearing – Declination] 

Calculate True Bearing From Magnetic Bearing- Example

Example: The magnetic bearing of a line OP is 89°45՛. Determine the true bearing if – a) The magnetic declination is 5°30՛ E. b) The magnetic declination is 4°15՛ W.

Solution: a) In fig. (i) True Bearing = (Magnetic Bearing + Declination) = (89°45՛ + 5°30՛) = 95°15՛.  

b) In fig. (ii) True Bearing = (Magnetic Bearing – Declination) = (89°45՛ – 4°15՛) = 85°30՛.

Whole circle bearing(WCB) and Quadrantal bearing(QB) are the two types of bearing which is used in the field of surveying for the purpose of measurement of the bearings

WHAT IS WHOLE CIRCLE BEARING?

• The whole circle bearing (WCB) is defined as the bearing of the line at any point which is measured with respect to the Meridian is known as Whole circle bearing.
• The Whole Circle bearings values range from 0° to 360°.
• The Whole circle bearing is generally used in the Prismatic compass.
• The whole circle bearing is used to measure the angle in the clockwise direction from the magnetic North.
• The Prismatic compass is graduated by Whole circle bearing.

Example of Whole Circle Bearing (WCB)

• If the survey line falls between the first quadrant 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 of any line, can exceed up to 90°, it can be reduced to the corresponding angle which is less than 90°, and has the same numerical value to the trigonometrical functions.
• This type of angle is also known as a Reduced bearing.
• The examples of whole circle bearing are as follows.
• 30°,45°,80°,120°,230°, and 320°, etc

What Is Quadrantal Bearing?

The Quadrantal bearing is also known as a Reduced bearing. Quadrantal bearings are generally measured from the North or South direction towards the East or West direction.

The quadrantal bearing varies from 0° to 90°.

In the quadrantal bearing or reduced bearing system, the bearings are taken either from the magnetic North or the magnetic south direction. It will depend on which one is nearer to that line.

In the Quadrantal bearing system, magnetic North and magnetic South lines are considered as a reference line.

Example of Quadrantal Bearing

In the quadrantal bearing system, you can take both clockwise as well as the anticlockwise angle from the reference line.

It is necessary to state the particular quadrant in which that line lies. The letters N(north), S(south), E(east), and W( west) are used to represent the quadrant.

Reduced bearing is observed by the surveyor’s compass.

The quadrants are represented are as follows.

1st quadrant = N – E

2nd quadrant = S – E

3rd quadrant = S – W

4th quadrant = N – W

The example of the quadrantal bearing are as follows

N35°E,S49°E,N65°W,S25°W etc.

DIFFERENCE BETWEEN WHOLE CIRCLE BEARING AND REDUCED OR QUADRANTAL BEARNING 

Sr.No.	Whole Circle Bearing	Quadrantal Bearing
1	The horizontal angle which is made by the survey line, with the magnetic north in a clockwise direction is known as the Whole circle bearing.	The horizontal angle which is made by a survey line with the magnetic North or South whichever is near the line in the eastward or westward direction is known as quadrantal wearing or reduced bearing.
2	In the whole circle bearing, the magnetic North line is considered as the reference line.	In the quadrantal Bearing, both magnetic North as well as South lines are considered as a reference line.
3	In the whole circle bearing only clockwise angle is taken from the reference survey line	In the quadrantal bearing both clockwise, as well as the anticlockwise angle from the reference line, is taken
4	The value of the whole circle bearing ranges from 0°  to 360°	The value of the quadrantal wearing for reduced bearing ranges from 0° to 90°
5	The example of a whole circle bearing are 30°,45°,80°,120°,230°, and 320°, etc	Example of quadrantal bearing or reduced bearing are N35°E, S49°E, N65°W, S25°W, etc.

 

Fore Bearing And Back Bearing 

  

Bearing measured from one station to adjacent next station in the direction of traverse is called fore bearing. 

Bearing measured from one station to adjacent previous stations in the opposite direction to traverse is called back bearing.

That fore bearing and back bearing of a line have a difference of 180°.