Methods of Ranging in Chain Surveying | Guide to Surveying and Levelling
In measuring a survey line, the chain has to be laid out on the ground between the stations.
If the line is short, the chain could be put in alignment easily but if it is long or the end station is not clearly visible, then intermediate points has to be established in line with end points to know the directions of the line by ranging.
Types of Ranging
There are two types of ranging:
- Direct ranging
- Indirect ranging
Direct ranging is possible when the stations are intervisible.
Ranging is done by eye-judgement. Ranging rods are erected vertically beyond each end of survey line.
The surveyor stands 2m beyond the ranging rod while the assistant folds the ranging rod vertically in the intermediate stations.
The ranging rod is held roughly in line by the thumb and fore-finger.
The surveyor directs the assistant to move the rod to the left or right until the three ranging rods appear to be in a straight line.
To avoid errors due to the ranging rods not being vertical, the lower end of the rod are cited for alignment.