Fore Bearing And Back Bearing In Surveying Pdf

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fore bearing and back bearing in surveying pdf

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The bearing we end up with represents the angle between a line from magnetic north to our location, and a line from our. Surveying is a very important part of civil engineering.

SURVEY FORE BEARINGS(FB) & BACK BEARINGS(BB)

Bearings of lines may be calculated if bearing of one of the lines and the included angles measured clockwise between the various lines are given. In a closed traverse, where local attraction is not suspected i. The ordinary compass cannot read directly the angle between two lines.

The angles can be determined by observing the bearings of the two lines from their point of convergence. When the two lines meet at a point, two angles interior and exterior and formed.

The following rules may be employed to find the angles between the lines whose bearings are given. Subtract the smaller bearing from the greater one.

Express both the bearings as if they are measured from the point where the lines intersect and then apply the above rule. The angle BAC can then be obtained by the application of the above rule.

In this case, to avoid unnecessary labour, firstly draw a rough sketch showing the directions of the lines and then proceed as follows. Since the lines are meeting at the same point O, the included angle will be the difference of the two bearings.

What is the bearing of BC?

Bearing (angle)

Bearings of lines may be calculated if bearing of one of the lines and the included angles measured clockwise between the various lines are given. In a closed traverse, where local attraction is not suspected i. The ordinary compass cannot read directly the angle between two lines. The angles can be determined by observing the bearings of the two lines from their point of convergence. When the two lines meet at a point, two angles interior and exterior and formed.

Local attraction is the phenomenon by which the magnetic needle is constantly prevented to point towards the magnetic north at a place. This is because that these magnetic compass is influenced by other magnetic objects at that locality such as wires carrying electric current, rails, steel and iron structures, steel tapes etc. The occurrence of local attraction can be detected by observing the difference between the fore and back bearings. If there is no influence of local attraction and other error, this difference will be So we can then conclude that both stations are free from local attraction. Due to local attraction significant amount of error can be occur in compass surveying observations and they will be same on all the bearings. Local attraction can be minimized using following methods:.

In navigation , bearing is the horizontal angle between the direction of an object and another object, or between it and that of true north. In nautical navigation the absolute bearing is the clockwise angle between north and an object observed from the vessel. If the north used as reference is the true geographical north then the bearing is a true bearing whereas if the reference used is magnetic north then the bearing is a magnetic bearing. An absolute bearing is measured with a bearing compass. The measurement of absolute bearings of fixed landmarks and other navigation aids is useful for the navigator because this information can be used on the nautical chart together with simple geometrical techniques to aid in determining the position of the vessel.


The bearings obtained in surveyor's compass are the quadrantal bearings. Fore and back Bearing. The bearings of a survey line in the direction of the survey is.


Calculation of Angles from Bearings | Compass Surveying | Surveying

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Taking a forward bearing. The first compass bearing we need to take is from our known location to our cabin on the far shore. The bearing we end up with represents the angle between a line from Magnetic North to our location, and a line from our location to the cabin. These bearings in the opposite direction are called back bearings or reciprocal bearings. How to determine a back bearing.

Bearings measured in the direction of progress of the survey are known as fore bearing and bearings measured opposite to the direction of the survey are known as back bearing. The bearing of a line is the direction with respect to a given meridian; Meridian is a fixed reference line. While setting out a survey line, the bearing readings are necessary. Fore Bearing - Bearing measured in the direction of progress of the survey. Back Bearing - Bearing measured opposite to the direction of survey. Hope you are pretty familiar with bearing, types of bearing and some of the related terms. In the figure below, OA is the survey line to be set out.

Taking a forward bearing. The first compass bearing we need to take at the lake is from our unknown location to our cabin on the far shore. The bearing we end up with represents the angle between a line from Magnetic North to our location, and a line from our location to the cabin. How to determine a back bearing One technique is to do the math. Forward and back bearings as seen through a sighting compass. There are also lots of tricks that avoid doing the arithmetic entirely…. Most sighting compasses show the back bearing in a smaller font size above or below the forward bearing.

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