Explain Orientation of plane table by Back-sighting Method.

Explain Orientation of plane table by Back-sighting Method.
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Ans:- The method of setting up the plane table at each of the successive stations parallel to the position it occupied at the starting station is known as an Orientation. Orientation must be done when the plane table is set up at more than one station.

Procedure of back sighting Method: a)Suppose A and B are two stations. The plane table is set up over A. The table is levelled by spirit level and centered by U- fork so that point ‘a’ is just over the station A. The North line is marked on the right hand top corner of the sheet by trough compass. b)With the alidade touching ‘a’, the ranging at ‘B’ is bisected and ray is drawn. The distance AB is measured and plotted to any suitable scale. So the point ‘b’ represents station B. 

c) The table is shifted and set up over ‘B’. It is levelled and centered so that ‘b’ is just over ‘B’. Now the alidade is placed along the line ‘ba’ and the ranging rod at ‘A’ is bisected by turning the table clockwise or Anti clockwise. At the same time the centering may be disturbed and should be adjusted immediately if required. Then the centering, levelling and bisection of the ranging rod at a are perfect then orientation is said to perfect.

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Explain the process of chaining on sloping ground by stepping method with neat sketch.

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Define- 1. Whole circle bearing 2. Reduced bearing 3. Fore bearing 4. Back bearing

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Define ‘ Fore bearing ’ & ‘ back bearing ’ of line with a neat sketch

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Define the terms - Foresight, back sight, intermediate sight and change point.

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Define the terms - dip of needle, magnetic bearing, fore bearing and back bearing.

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