Numerical Examples for Errors in Chain Surveying

A practical Example for Calculation of the True Area of the field | Errors in Chain Surveying

In my previous article, we studied how to measure true distance considering the Errors occurring in Surveying.

Correction formulas to be kept in mind (for incorrect length of Chain)

True distance = L’/L*measured distance

True area = (L’/L)2*measured area

True Volume = (L’/L)3 * measured volume

Where, L’ = incorrect length of chain

L = correct length of chain

The chain was tested before starting the surveying and was found to be 20m. At the end of surveying, it was tested again and was found to be 20.12m. The area of the plan of the field drawn to a scale 1cm = 6m was 50.4sqm. Find the true area of the field in sqcm.

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Chaining on Sloping Ground | Guide to Surveying and Levelling

Chaining on Sloping Ground | Surveying and Levelling

There are two methods for determining horizontal distance on sloping ground.

  1. Direct Method
  2. Indirect Method

Direct Method of Chain Surveying

This method is also known as “Stepping Method”.

The horizontal distances are directly measured by the process of stepping.

Procedure

A path of chain or tape is stretched out from ‘P’.

The path length of chain or tape depends on the steepness of the ground.

The follower holds the zero end of the chain at ‘P’ and directs the leader at P1 to be in the line of PQ and stretch the chain or tape above the ground in horizontal line.

Direct Method | Chain Surveying
Direct Method | Chain Surveying

The leader then transfers the point ‘P1’ to P2 on the ground by means of plumb bob or dropping a pebble or an arrow,

Now the followers take the new position ‘P2’ and directs the leader to move forward and stretch the tape or chain in a line of PQ.

Now the followers take the new position ‘P2’ and directs the leader to move forward and stretch the tape or chain in a line of PQ and the new position is P3.

Again the leader transfers the point P3 to P4 on the ground as done earlier.

This process is repeated till the point Q is reached.

Horizontal distance PQ = S1 + S2 + S3 + S4 + S5

Read moreChaining on Sloping Ground | Guide to Surveying and Levelling

Types of Levelling Instruments | Definitions in Levelling

Various types of Levelling Instruments and Important Definitions | Surveying

  1. Dumpy level
  2. Y-level
  3. Modern Tilting level
  4. Automatic level

The levelling instruments essentially consist of the following:

A levelling head with three foot screws which enables to bring the bubble at its centre.

Telescope that provides line of sight to bisect distinct objects.

A bubble tube to make the line of sight horizontal either mounted on top or side of the telescope.

A tripod for supporting the levelling instrument.

Important Definitions in Levelling

Line of Collimation or line of sight

The line joining the point of intersection of the cross wires of the diaphragm to the optical centre of the objective and its imaginary continuation.

Reduced Level

The vertical distance measured above or below the mean sea level or benchmark is called as reduced level.

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Sources of Errors in Surveying | Civil Engineering

Sources of Errors in Surveying

In this article, we will discuss three major types of errors that are found to be very common in Surveying.

Types of Errors
Types of Errors

Types of Errors

  1. Instrumental errors
  2. Personal errors
  3. Natural errors

Instrumental errors

Error may arise due to imperfection or faulty adjustment of the instrument with which measurement is being taken.

For example:

A tape may be too long or an angle measuring instrument maybe out of adjustment. Such errors are known as Instrumental erros.

Read moreSources of Errors in Surveying | Civil Engineering