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Indirect ranging
Indirect ranging or Reciprocal ranging
Indirect ranging is resorted to when both the ends of the survey line are not intervisible either due to high intervening ground or due to long distance between them. In such a case, ranging is done indirectly by selecting two intermediate points M1 and N1 very near to the chain line in such a way that from M1 both N1 and B are visible, while from N1 both M1 and A are visible.
Two surveyors station themselves at M1 and N1 with ranging rods. The person at M1 then directs the person at N1 to move to a new position N2 in line with M1B. The person at N2 then directs the person at M1 to move to a new position M2 in line with N2 A. Thus the two persons are now at M2 and N2 which are near to the chain line than the positions M1 and N1. This process is repeated till the points M and N are located in such a way that the person at M finds the person at N in line with MB and the person at N finds the person at M in line with NA. After having established M and N other points can be fixed by direct ranging.
Two surveyors station themselves at M1 and N1 with ranging rods. The person at M1 then directs the person at N1 to move to a new position N2 in line with M1B. The person at N2 then directs the person at M1 to move to a new position M2 in line with N2 A. Thus the two persons are now at M2 and N2 which are near to the chain line than the positions M1 and N1. This process is repeated till the points M and N are located in such a way that the person at M finds the person at N in line with MB and the person at N finds the person at M in line with NA. After having established M and N other points can be fixed by direct ranging.
Last modified: Thursday, 21 April 2011, 10:30 AM