Surveying
Surveying is the art of making suitable measurements in horizontal or
vertical planes. This is one of the important subjects of civil engineering.
Without taking a survey of the plot where the construction is to be carried
out, the work cannot begin.
Surveying Chart
Levelling
Levelling is the art of representing relative positions in the vertical plane of
different points on the earth’s surface.
It helps in determining the areas that are to be levelled to achieve a certain
slope.
Principles of Surveying
All the surveys that are conducted are based on two fundamental principles.
They are as follows:
1. Working from whole to part
2. Fixing a point with reference to two fixed points
Working from whole to part
In order to localize errors and prevent their accumulation, a set of control
points is always established with great precision first for the whole area to
be surveyed.
Later on, details or filled in between these control points to a relatively
smaller precision.This fundamental work principle is known as “Working
from whole to part”.
Fixing a point with reference to two fixed points
Survey stations are fixed by at least two measurements, either both linear or
angular measurements or linear and angular measurements from two control
points.
Let A and B be two control points. Another point C can be located by any of the
following methods:
By two distances AC and BC
The point C is plotted by intersection of arc taking AC and BC as radius and
with centres A and B.
Two Distances Method
By perpendicular distance CD and distance AD
Perpendicular distances Method
By angle <CAB and distance AC
Angle Method
By the angles BAC and ABC
Two Angles Method
By the <ABC and distance AC
Arc and Angle Method
Chain Surveying or Linear Surveying
It is the method of land surveying in which only linear measurements are
made.
Chain surveying requires chain, tape and ranging rods.
Chain surveying is not suitable for large areas having many details.
(The term “details” means a natural or manmade features at or near the
ground surface).
Chain Surveying
It consists of the following:
Hard details
Hard details include buildings, roads, walls etc.
Soft Details
Soft details include river, vegetation, trees etc.
Overhead details
Overhead details include power and telephone lines.
Underground details
Underground details include survey of water mains, sewer etc.
Principles of Chain Survey
A triangle is a simple figure which can be plotted from the lengths of three
sides even if the angles are not known.
In chain survey, the area to be surveyed is divided into a framework
consisting of triangles.
Selection of survey station and Survey lines

The main station should be mutually intervisible so that ranging can be
done easily.

Survey lines should be as few as possible so that framework of triangles
can be plotted easily.

Survey lines should pass through a level open ground as far as possible
so that chaining can be done easily.

The frame should have atleast one long baseline that runs through the
middle of the area.

The main survey lines should form well conditioned triangles with no
angles less than 30 degrees or more than 120degrees.

The survey lines should be selected such that there are no obstacles in
chaining and ranging.

The survey lines will be close to the details to avoid long offsets.

If required, number of subsidiary stations should be selected and
subsidiary lines run to avoid long offsets.

Each triangle should have a check line to detect mistakes in
measurements and plotting.

While selecting main stations and survey lines, the basic principles of
surveying of working from whole to the part should be followed.
Field work in Chain surveying | Surveying and Levelling
Earlier, we discussed “Principles of Chain Surveying” and the considerations
that are taken for carrying out Chain Surveying… In this article, we will
discuss various instruments that are essential for carrying out Chain
Surveying.
Here are the steps to be followed for carrying out Chain Surveying:
1. Reconnaissance Survey
2. Marking stations
3. Running survey lines
4. Taking offsets
Instruments used in Chain Survey
1. Chain, 20m or 30m long
2. Tape
3. Arrows
4. Ranging rods
5. Wooden or Iron Pegs
6. Plumb bob
7. Cross staff
Chain used for Surveying
20m chain – 100 links
30m chain – 150 links
1 links – 20cm
Links of chain are made by mild steel wire – 4mm diameter.
Chain used for Chain Surveying
Each link at the end is bent into a loop and is connected to adjoiningly by
means of three oval rings which offers flexibility to the chain. Ends of chains
carry brass handle.
The length of chain is the distance between the outside of handles.
Brass Tags in Chains
Brass tags are fixed at every 5m length.
Tape used for Chain Surveying
Metallic Tape
Cloth tapes reinforced with brass, copper and bronze wires to prevent it
from stretching.
They are available in lengths 10, 15, 20 and 30m.
Tape is provided in leather case fitted with winding device.
It is used for small linear measurements and for taking offsets.
Steel Tapes
Outer end of the tape carries better links for its easy handling and the length
of tape is inclusive of this ring.
It is provided in a leather case or a rust-proof metal case with a suitable
winding device.
Steel tapes are light, delicate and are used for measurements of distance
with high degree of accuracy.
Arrows
Arrows or marking pins or chaining pins are used to mark the end of each
chain during the process of chaining.
400mm in length are pointed at one end for intersecting into the ground and
bend into a ring at the other end for facility of carrying.
A piece of white or red tape tied to the ring so that they can be made easily
visible at a distance.
Ranging Rods
2m to 3m length and 2.5m diameter painted alternately with black or white.
An iron shoe provided at its bottom enable it to the fixed at a required point
in the ground.
Ranging rods
A coloured flag is provided at its tops so that it can be easily seen from a
long distance.
They are used for ranging intermediate points along a given survey line and
are also used to mark the positions of survey stations clearly.
Wooden or iron pegs
15cm long and 25mm to 30mm square cross-section prevail into the ground
by wooden or steel hammer.
Iron peg – 15cm long (1cm diameter)
Wooden or Iron Pegs
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
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
Indirect Method of Chain Surveying
In this method, the sloping side is measured on the ground and later it is converted into the
horizontal equivalent using geometrical condition.
The following methods are adopted for calculating horizontal distance indirectly:

By measuring angle of inclination

By measuring difference of levels

By hypotenusal allowance
Methods of Ranging in Chain Surveying | Guide to Surveying and Levelling
In measuring a survey line, the chain has to be laid out on the ground between the stations.
If the line is short, the chain could be put in alignment easily but if it is long or the end station is
not clearly visible, then intermediate points has to be established in line with end points to know
the directions of the line by ranging.
Types of Ranging
There are two types of ranging:
1. Direct ranging
2. Indirect ranging
Direct ranging
Direct ranging is possible when the stations are intervisible.
Ranging is done by eye-judgement. Ranging rods are erected vertically beyond each end of
survey line.
The surveyor stands 2m beyond the ranging rod while the assistant folds the ranging rod
vertically in the intermediate stations.
The ranging rod is held roughly in line by the thumb and fore-finger.
The surveyor directs the assistant to move the rod to the left or right until the three ranging rods
appear to be in a straight line.
To avoid errors due to the ranging rods not being vertical, the lower end of the rod are cited for
alignment.
Indirect Ranging
1. Indirect Ranging is possible when the ends of a line are not inter-visible as in the case when a
hill ground or when the distance between the stations are so large that they are not clearly intervisible.
Indirect Ranging
Intermediate points are fixed by the process of reciprocal ranging as explained below.
Let A and B be the ends of a survey line to be measured as a rising ground between them.
Two chain men with ranging rods take the positions M1 and N1 such that they are as nearly in
line with A and B as they could judge the chain men at M1 could N1 and B.
And the chain men at N1 could see M1 and A.
First chain men at N1 directs M1 to M2 so that he comes in the line with A and N.
Then the chain man at M2 directs N1 to N2 such that he comes in line with B and M2.
The process is repeated so that they align each other successively directing each other until they
are both finally in the line AB.
Types of Errors occurring in Chain Surveying
There are two types of Errors that are commonly seen to occur in Chain Surveying. For students
studying the concept of Chain Surveying, study of the occurrence of different types of Errors in
Chain Surveying is important. In this article, we will briefly discuss different types of Errors in
Chain Surveying and the situations in which they occur.
Types of Errors:
1. Cumulative error
2. Compensative error
Cumulative error
These errors always accumulate in one direction and are serious in nature. They affect the survey
work considerably.
They make measurements too long or too short.
These errors are of two types and are known as systematic errors.
They are classified as follows:
1. Positive error
2. Negative error
Positive error
These errors make the measured length more than the actual length which results into wrong
calculations by the Surveyor.
The following are some of the positive errors:

The length of chain is shorter than the standard length due to bending of links, removal of
connecting rings and knots in links.

The temperature is lower than at which the tape was calibrated.

Not applying sag correction.

Sag takes place due to self weight of the chain.

Incorrect alignment
Negative errors
These errors make the measured length less than the actual length.
Following are some of the negative errors:
Length of chain or tape greater than its standard length due to flattening of rings, opening of
ring joints and temperature being higher than at which it was standardised.
Compensative errors
These errors occur in either direction and are likely to compensate.
These occur in following situations:

Incorrect holding of chain

Displacement of arrows

Adding or omitting a full length of chain

Reading wrongly

Booking wrongly
ape Correction, Sag Correction, Pull Correction and Temperature Correction
In this article, I will list out different formulas for the respective corrections…
Tape Correction
The following corrections are to be made for measurements taken with a tape because tape can
never be practically used under specified standard conditions.
Correction for absolute length
Absolute length of tape is its actual length under specified condition
Ca = Lc/L
Where, Ca = correction to be applied to the tape in ‘m’
Lc = measured length in ‘m’
L = nominal length of tape in ‘m’
Correction for temperature
Length of tape is increased with the increase of temperature and decrease with decrease of
temperature.
Ct = A (Tm – Ts)
Where,
A = coefficient of thermal expansion per one degree Kelvin
Tm = temperature during the measurement in Kelvin
Ts = temperature at which the tape standardised in Kelvin
Correction for Sag
When the tape is suspended from two ends in air
Sag correction, Cs = L/24(W/P)2
Where, L = horizontal distance between supports in meters
W = weight of tape in Newtons
P = Pull applied in Newtons
Correction for Pull
If the pull during measurement in not the same at which the tape is standardised then the
correction for pull is necessary.
Cp = [(P – P0)/AE) * L]
Where,
P = pull in Newtons
L = length of measured line in ‘m’
P0 = standard pull in Newtons
E = Young’s Modulus in N/mm2
Correction due to incorrect length of chain
This is like a formula list which is to be kept in mind while making Calculations:
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 length of a line measured with 20m chain was found to be 500m. It was subsequently found
that the chain was 0.04m too long. What is the length of line?
Correct length of chain, L’ = 20 + 0.04 = 20.04m
Length, L = 20m
Measured length, = 500m
True length = (L’/L) * measured length
= (20.04/20) * 500
= 501m
Related posts:
Scales | Engineering Surveying
Scale is a fixed ratio that every distance on the plan bears with corresponding distance on the
ground.
Rulers bearing a certain specific scale for measurement
Scale can be represented by the following method
One centimetre on the plan represents some whole number of the metres on the ground.
1cm = 10m
This type of scale is called engineering scale.
1 unit of length on the plan represents some number of same units of length on the ground.
1/1000 etc…
This ratio of map distance to the corresponding ground distance independent of units of
measurement is called Representative Factor (RF).
For example,
1cm = 50m
RF = 1/(50×100) = 1/5000
Above two types of scales are also known as numerical scales.
There are four main types of scales which are used for different purposes for measurements:
1. Plain Scale
2. Diagonal Scale
3. Vernier Scale
4. Scale of chords
Scales | Engineering Surveying
Scale is a fixed ratio that every distance on the plan bears with corresponding distance on the
ground.
Rulers bearing a certain specific scale for measurement
Scale can be represented by the following method
One centimetre on the plan represents some whole number of the metres on the ground.
1cm = 10m
This type of scale is called engineering scale.
1 unit of length on the plan represents some number of same units of length on the ground.
1/1000 etc…
This ratio of map distance to the corresponding ground distance independent of units of
measurement is called Representative Factor (RF).
For example,
1cm = 50m
RF = 1/(50×100) = 1/5000
Above two types of scales are also known as numerical scales.
There are four main types of scales which are used for different purposes for measurements:
1. Plain Scale
2. Diagonal Scale
3. Vernier Scale
4. Scale of chords
Importance of Contouring in the field of Surveying
Contouring is an imaginary line on the ground obtained by joining points having same elevation.
Characteristics of Contours
Contour lines are closed, however they may be close on the map itself or outside the map
depending upon the topography.
The spacing between contour lines depends upon the slope of the ground.
In steep slopes, the spacing is small, for gentle slopes the spacing is large.
If the contour lines are equally spaced, they indicate uniform slope.
Contour Analysis
If the contour lines are parallel, straight or equally placed, they represent plane surface.
In a series of contour lines on the plan or map indicates either a hill or depression.
In case of the hill, the values of the elevation go on increasing towards the centre whereas in case
of depression, the values go on decreasing towards the centre.