To range out a survey line when the two ends of a line are inter-visible from each end.

Object: To ray out a survey line when the stations are intervisible.

Instruments required:

1. Ranging rods

Theory:

Ranging is the process of fixing intermediate stations between two fixed end stations in order to make the line straight and to find accurate horizontal distance. In measuring the length of a survey line, it is necessary that the tape should be laid out on the ground in a straight line between the end stations.

Thus it is necessary to place intermediate ranging rods to maintain the direction of line in straight path. Ranging is of two types, It is called direct ranging, when the two end stations are intervisible to each other and It is called indirect ranging, when the two end stations are not intervisible to each other.

Procedure :

• To begin with, the ranging rods should be fixed vertically behind each end of the line. The two end stations are called terminal stations.
• Hold the rod firmly in the hand with its lower end about 30 cm above the ground and then drive it firmly into the ground by a quick downward blow.
• If not driven sufficiently, remove it and enlarge the hole with the help of ranging rod and drive it a second time.
• In case of hard surface, it should be supported by a pile of stones.
• To range a line, the surveyor stands about 2m behind the ranging rod at the beginning of line, while the assistant holds the ranging rod vertically at arm’s length at the point where it is desired to establish the intermediate station.
• The surveyor then directs the assistant to move his rod to right or left until the three ranging rods appear to be exactly in a straight line.
• The surveyor then signals the assistant to fix the rod.
• In this way a line can be ranged by eye when two end stations are intervisible to each other.

Note: There may be more than one intermediate station established.

Observation:

The observed readings of direct ranging involve four intermediate ranged stations C, D, E and F between two end stations A and B and use of six ranging rods, all in line with each other.

Chaining a survey line:

In all surveying operations, two men called Chainmen are required. The chainman at forward end of the chain is called the surveyor, while the chainman at rare end of the chain is known as follower.

Duties of surveyor are:

1. To place the follower in line with the ranging rod at the forward station.
   
2. To call out instructions to the follower.
   
3. Always to carry the rare handle in his hand and not to allow it to drag on the ground.
   
4. To pick up the arrows inserted by the follower.
   

Duties of follower are:

1. To drag the chain forward.
   
2. To insert arrows at the end of every chain.
   
3. To obey instructions of the surveyor.
   

Note: The chainman who is more intelligent and experienced should be selected as the surveyor, as upon his care and judgment depends upon the accuracy of measurements.