2.5 Classification of ranging

We can classify various types of ranging as follows:

i. Direct ranging

• This method is used if the first and last points are intervisible. 
• The number of ranging rods required for this method is three. 

Steps for direct ranging: 

• Two points A and B are inter visible and points/stations C is the intermediate point.
• Ranging rods are fixed at point A and B. 
• Another ranging rod is hold at C.
• Surveyor stays 2m away from either A or B and looks along line AB. 
• S/he directs assistant to move at right angle to line AB until all 3 ranging rods are aligned. 
  

ⅱ. Indirect ranging

• This method is used if ranging rod at B is not visible due to intervening ground.
• It is also called reciprocal ranging. 
• The number of ranging rod required for indirect ranging is four.

Steps for indirect ranging 

• Two points A and B are not visible and Mand N are the intermediate points.
• Ranging rods are fixed at A and B 
• Points A & B are visible from M and N.
• Surveyor at A directs assistant at M to move such that A, M & N are aligned in a line.
• Similarly surveyor at B directs assistant at N to move such that B, M and N are aligned in a line.
• This process is repeated until A,M,N,B are in a line.