Aquaculture Engineering

Experiment No 1 - Obstacle to chaining and ranging

Practical - 2
Obstacle to chaining and ranging

In chain surveying, sometimes the chainman is unable to measure the distance between two points directly, due to obstacles. Hence it has to be found out by indirect measurements. Basically there are three types of obstacles

• Obstacle to ranging but not chaining
• Obstacle to chaining but not ranging
• Obstacle to both chaining and ranging

Experiment 1: Obstacle to ranging but not chaining
In this type of obstacle the ends are not intervisible and it is quite common, except in a flat country.

AB is the line in which A and B are not visible from intermediate point on it. Through A, draw a random line AB1 in any convenient direction but as nearly towards B as possible. The point B1 should be chosen in such a way that B1 is visible from B and BB1 is perpendicular to the random line. Measure BB1. Select C1 and D1 on the random line and erect perpendicular C1C and D1D on it. Join CD and prolong.