Chapter 2 Linear measurement

1. Chapter 2
Linear Measurement

2. Classification of surveying:
According to the instruments used, the surveying is classifieds follows
1. Chain Surveying
2. Compass Surveying
3. Theodolite Surveying
4. Plane Table Surveying
5. Tachometric Surveying

3. Instruments used for chain surveying:
The following instruments are used while chaining
1. Chain
2. Arrows
3. Ranging Rod
4. offset
5. Pegs
6. Plumb bob
7. Tape

4. Chain:- Chains are used to measure horizontal distances. Chains are
formed of straight links of galvanized mild steel wire called links. The
ends of each link are bent into a loop hand connected together by means
of three oval rings which afford flexibility to the chain.

5. Arrows: Arrows or making pins are made of tempered steel wire 4mm in diameter
and generally 10 arrows are supplied with a chain. An arrow is inserted into the
ground after the chain length is measured on the ground. Usually, the length of an
arrow is 40cm and one end of it is made sharp and the other end is bent into a circle
for facility of carrying.
Ranging Rods: The ranging rods are used for making the positions of stations and
for ranging the lines. They are made of ell seasoned straight grained timber teak.
They circular in cross section of 3cm diameter and have a length of either 2 or 3cm,
length being more common. They are shod at the bottom with a heavy iron point. In
order to make them visible at a distance, they are pained alternatively black and
white or red and white.
Offset: Offset rod is similar to that of ranging rod. They are should with pointed
iron shoe at one end, ad provided with a notch or a hook at the other for pulling or
pushing the chain through a hedges or other obstructions.

6. Pegs: Wooden pegs are used to make the positions of the station’s terminal point of
a survey line. They are made of hard timber, generally 2.5cm or 3 cm square and 15
cm long tapered at the end.
Plumb Bob: while chaining along sloping ground a plump bob is required to
transfer the point of a ground. It is also used for accurate centering of the theodolite
compass, Plane table etc. over a station mark and for testing the vertically of
ranging pole.
Tapes: The measuring tapes are usually found in the following four different kinds
according to the materials from which they are manufactured
1. Lenten or cloth tapes
2. Metallic Tape
3. Steel Tape
4. Invar tape

7. Error in Length due to incorrect chain
It May be noted that distance measured with the chain or tape of incorrect or Erroneous
length will not be correct. The correct distance can be calculated from the following formula:
Correct or T.D = M.D x L’/L
Where T.D = True Distances
M.D = Measuring Distance
L’ = Incorrect Length of chain or tape
L = Correct Length of chain or tape
Error in Area due to incorrect chain
It May be noted that distance measured with the chain or tape of incorrect or Erroneous
length will not be correct. The correct distance can be calculated from the following formula:
Correct or T.D = M.D x (L’/L)2
Where T.D = True Distances
M.D = Measuring Distance
L’ = Incorrect Length of chain or tape
L = Correct Length of chain or tape

8. Error in Volume due to incorrect chain
It May be noted that distance measured with the chain or tape of incorrect or
Erroneous length will not be correct. The correct distance can be calculated from t
he following formula:
Correct or T.D = M.D x (L’/L)3
Where T.D = True Distances
M.D = Measuring Distance
L’ = Incorrect Length of chain or tape
L = Correct Length of chain or tape
ERRORS IN SURVEYING
Surveying is a process that involves observations and measurements with a
wide range of electronic, optical and mechanical equipment some of which are
very So hesitated.
Despite the best equipment's and methods used, it is still impossible to take
observations that are completely free of small variations caused by errors which
must be guided against or their effects corrected.

9. TYPE OF ERROR
Gross Error
A blunder (or gross error) is a significant, unpredictable mistake caused by
human error that often leads to large discrepancies. Blunders are typically the result
of carelessness, miscommunication, fatigue, or poor judgment.
Systematic or Cumulative Error
A systematic error always follows some definite mathematical or physical
law, and a correction can be determined and applied. Such errors are of constant
character and are regarded as positive or negative according as they make the result
too great or too small.
Random or Compensating Error
The error that occurs during the chaining process in the same direction is
called as cumulative error. This type of error accumulates with the process of
chaining. An error that occurs in either directions during the chaining process is
called as compensating error.