Linear Measurement Techniques in Surveying: Chain Surveying and Obstacle Measurement, Study notes of French

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There are 3 methods of making linear measurements

◦ Direct Method  Distances measured using a chain or tape ◦ Optical Method  observations are taken through a telescope  Eg: tacheometer ◦ Electro- magnetic Method  Distances measured using electromagnetic waves  Eg: total station

 Distance = No. of paces x average length of the pace

 Used for preliminary surveys

Pace

 A small instrument which counts the number of paces

 Distance = No. of paces x Average length of the pace

 A device similar to passometer adjusted to the length of the pace of the person carrying it

 Registers the total distance covered

 Chain surveying is the simplest method of surveying in

which only linear measurements are made and no

angular measurements are taken

Basic principle - Triangulation

 The area is divided into a network of triangles & the

sides of various triangles are measured directly in the

field with chain or tape

 Metric chain

 Gunter’s chain or surveyor’s chain

 Engineer’s chain

 Revenue chain

 Steel band or band chain

Laths

Plumb bob

Tapes

Ranging rod

Pegs

Arrows

Arrows

Check lines or proof lines

 Lines to check the accuracy of the work

 Length measured in field must agree with its length in the plan

Tie lines

 Line joining the subsidiary or tie stations on the main line

 Tie lines takes the details of nearby objects, also serve the purpose of a check line

D C

A

B

 Various obstacles or obstructions such as woods/trees,

hills, ponds, rivers, buildings, etc are continually met

with in chaining.

 Chaining should be continued in straight line.

 For that, special methods are therefore employed in

measuring distances across the obstructions

(i) Both ends of the line may be visible from intermediate points

on the line

(ii) Both ends of the line may not be visible from intermediate

points on the line

Eg: hill, forest etc

Reciprocal ranging