Practical 4 - Object is to ray out a survey line when the stations are not intervisible. PDF

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Object is to ray out a survey line when the stations are not intervisible.
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Practical # 4 Object : a) To ray out a survey line when the stations are not intervisible. Instruments required : 1. Ranging rods Theory : Indirect Ranging is possible when the ends of a line are not inter-visible as in the case when a hill ground or when the distance between the stations are so large that they are not clearly inter-visible. In such a case, intermediate points can be fixed on the line by process known as indirect or reciprocal ranging.

Procedure:  Let A and B be the two end stations with rising ground or a hill between them.  Let the two chainmen with ranging rods take positions at P1 and Q1 as nearly in line as they can judge.  The chainman at P1 can see both the ranging rods at Q1 and B.  The chainman at Q1 can see both the ranging rods at P1 and A.  The chainman at Q1 directs P1 to move to P2 so that he comes in the line with A and Q1.  Then the chainman at P2 directs Q1 to move to Q2 such that he comes in line with B and P2.

 The two chainmen then repeatedly proceed to align each other alternately.  By successively directing each other into line, their positions will be changed until finally they are both in the line AB exactly, i.e. the four ranging rods (A,P,Q,B) are in same straight line.  The positions of these ranging rods (P and Q) serve as intermediate stations for ranging the line and then fix all ranging rods firmly. Observation in the field:

End station 1

Intermediate station 1

Intermediate station 2

End station 2

A

P

Q

B...