Chain surveying

UNIT – II

Chapter  - 3 (A)

CHAIN SURVEYING

SURVEYING MEASUREMENTS

The measurements used in surveying to obtain a plan or map of the area surveyed are:

1. Linear Measurement: Linear measurement deals with the distance between the points on horizontal or vertical plane. When the distance is measured in horizontal plane, it is called Horizontal Distance. If measured in the vertical plane, it is called Vertical Distance.

2. Angular Measurement: Angular measurement deals with the direction of a line with reference to any known direction or line. It is simply called as Angle. The angle when measured in horizontal plane, it is called Horizontal Angle. When measured in vertical plane, it is called Vertical Angle. Unit of measurement of angles is degrees or radians (it radians = 180°).

1. INSTRUMENTS USED IN SURVEYING

1. Tape and Chain are used for the direct measurement of length of a survey line in the horizontal plane.

2. Instruments like Cross Staff, Optical Square, Ranging Rods and Line Ranger are used for ranging and laying out a survey line.

3. Level and Hand Level are used for the measurement of distances in the vertical plane.

4. Theodolite, Prismatic Compass and Box Sextant are used for the angular measurements (i.e., direction) of a survey line.

5. Plane Table is used for making measurements and plotting of a survey line simultaneously."

2. METHODS OF MEASUREMENT OF DISTANCES

Measurement of distances between two points on the Earth's surface is done by two methods:

1. Direct Method: In Direct Method, distances are measured using Tapes, Chains, etc.

2. Computative Method: In Computative Method, the distances are obtained by computation (calculation) using Triangulation, Tachometry, etc.