Surveying

Surveying

1. SURVEYING

UNIT I INTRODUCTION AND COMPASS SURVEYING

Definition of surveying – Principles of surveying – Classification of surveying – field and
office work – Types of chain – Methods of Ranging.
COMPASS: Prismatic compass – Surveyor’s compass – Bearing systems and
conversions – Local attraction – Magnetic declination – dip.

Definition for Surveying
Surveying is an art of determining the relative positions of various points on,
above or below the surface of the earth by means of direct or indirect measurement of
distance, direction and elevation.
The object or purpose of surveying
The primary object of surveying is to prepare a plan or map to show the relative
position of the objects on the surface of the earth. It is also used to determine the areas,
volumes and other related quantities.
Principle of Surveying
General principles of surveying comprises of the following:
i) To work from the whole to the part
ii) To locate a new station by at least two measurements (angular, linear) from fixed
reference points
(i)To work from the whole to the part
 In any extensive survey it is necessary to establish a system of control points
with high precision.
 These points may be horizontal or vertical control points.
 Generally horizontal points are routinely needed, which are established by
triangulation or precise traversing.
 In order to attain the horizontal control points by triangulation, the area to be
surveyed is divided into large triangles.

2.  These triangles are established with great accuracy for which the triangles
should be nearly equilateral.
 These triangles are subdivided into small triangles which are surveyed with less
accuracy.
 Such type of working is to prevent the accumulation of error and to control and
locate minor errors.
 This process of working from whole to part is effective and accurate. On the
other hand, if the survey is done from part to whole the errors will be magnified
and uncontrollable at the end.
ii) To locate a new station by at least two measurements (angular, linear) from fixed
reference points
 New station should always be fixed by at least two measurements.
 These measurements may be linear or angular or both.
 Linear measurements are the horizontal distances measured by chain or tape.
 Angular measurements are the magnetic bearing or horizontal angle taken using
a prismatic compass or theodolite.
Classifications of Surveying

3. According to the purpose of surveying, instruments and methods employed etc., the
survey is classified as follows.

Classification of surveys based on,
(i) Purpose of surveying
(ii) Nature of the field
(iii) Methods employed
(iv) Instruments used
The above chart explains the various types of surveying.
Classification Based on the Purpose of Surveying
Surveying can be classified based on the uses and purposes which is as follows
1. Engineering Surveys
2. Military (or) Defence Surveys
3. Mine Surveys
4. Geological and Geographical Surveying
5. Archaeological Surveys
6. Route and Location Surveys
1. Engineering Surveys
 Engineering surveys are defined as the surveys, which are carried out to
implement the various engineering projects such as railways, roads, canals, dams,
industries, etc. and to calculate the quantities of work done.
2. Military or Defence Surveys
 The surveys carried out for the military and defence purposes in order to locate the
strategic positions in the enemy area are called Military (or) Defence Surveys.
 These surveys are conducted generally by aerial surveys.
3. Mine Surveys
 The surveys carried out for the presence of various minerals on (or) below the
ground surface are called Mine surveys and various special techniques are
involved in this mine surveying.

4. 4. Geological and Geographical Surveying
 The surveys carried out to ascertain the composition of earth crust are called
Geological surveys.
 The surveys carried out for the collection of data for preparing the geographical
map are called Geographical surveying.
 The geographical surveying is employed to serve different purposes such as
specifying national boundaries land use contours, etc.
5. Archaeological Surveys
 The surveys carried out to prepare the maps and to locate the relics of antiquities
and civilizations etc., are called Archaeological surveys.
6. Route and Location Surveys
 Route surveys are defined as the surveys, carried out for locating road (or) railway
networks.
 Location surveys are defined as the surveys, carried out to locate points on the
ground, based on the plans prepared.
Classification Based on the Nature of the Field
Based on the Nature of the Field (or Place of survey), the surveying can be classified as
follows.
1. Land Surveying
2. Hydrographic Surveying
3. Aerial Surveying
4. Underground Surveying
1. Land Surveying
 Land surveying are generally carried out, on land to prepare plans and maps of a
given area. Land surveys are also done for the purpose of partitioning the land,
calculation of (land) areas, location of boundaries of the properties etc.
Land surveys include the following:
(a) Topographical Surveys

5. (b) Cadastral Surveys
(c) City Surveys
(a) Topographical Survey
 The surveys carried out to prepare (or) to draw the topography of the mountainous
terrain, rivers, water bodies and other details of roads, railways, etc. are called
topographical surveys.
(b) Cadastral Surveys
 Cadastral surveys are defined as the, land surveys, carried out in a larger scale than
the topographical surveys for fixing the property lines, calculation of quantities of
areas and volumes etc.
(c) City Surveys
 The surveys carried out for the construction of roads, water supply system, sewage
system, parks, etc., for developing the township are called City Surveys.
 The city maps, prepared for the tourists are called Guide Maps.
 Guide Maps, for every important city Of India, are available from the offices of
the Department of Tourism.
2. Hydrographic Surveying
 Hydrographic surveys are defined as the surveys carried out for the purpose of
mapping of large water bodies for navigation, construction of harbours,
determination of shorelines, determination of Mean Sea Level (M.S.L), etc.
 Hydrographic survey includes the sounding techniques and some advanced
techniques.
3. Aerial Surveying
 The surveys carried out for determining the latitudes of different places on the
earth's surface and the direction of any line on the earth's surface by making
observations to heavenly bodies (such as Stars, Sun, Moon, etc.) are called
Astronomical surveys (or) Aerial surveys.
 An aerial survey is carried out from aircraft, which takes photographs of the
surface of the earth and wide areas can be covered by aerial surveys.

6. 4. Underground Surveying
 Underground surveys are carried out in the case of mines and tunnels.
 These are done by transferring the ground points to the underground level and
conducting surveys of tunnels, mines, caves, etc.
Classification Based on the Methods Adopted
These are the different methods of surveying depending on the instruments
available and the purpose of the survey. The general methods are as follows.
1. Triangulation Survey
2. Traversing Survey
3. Levelling Survey
4. Tacheometnc Survey
1. Triangulation Survey
 It is the basic method of surveying and in which, the measurement of one side of
the triangle (called base line) and the three angles is carried out.
 The other sides are calculated by using anyone of the suitable formulae available.
 If the three sides of the triangle are measured, then the method is called tri-
lateration.
2. Traversing Survey
 Traverse is defined as the survey work consisting continued survey lines either
closed or opened.
 The directions and the lengths are measured with a compass (or a theodolite) and a
chain (or a tape) respectively.
3. Levelling
 Levelling is the surveying method used to determine the elevations of the points.
 Level (or) levelling instruments is used for this survey, with a levelling staff.
 Contouring is the method of levelling surveying, in which the location of
horizontal points is determined.

7. 4. Tacheometric Surveying
 Tacheometric (or Tachometric) Surveying is the technique or method of surveying
in which, the horizontal distance can be calculated by using a special type of
theodolite (called Tacheometer), without the direct measurement of distances.
 It is based on the principle of Stadia Surveying.
5. Trigonometrical Levelling
 In this method, the distances and elevations are determined, by measuring the
vertical angles and by using the trigonometrical formulae.
Classification Based on the Instruments Used
Based on the instruments used and method of surveying, it can be classified as follows.
1. Chain Surveying
2. Compass Surveying
3. Plain Table Surveying
4. Level Surveying (or) Levelling
5. Theodolite Surveying
6. Tacheometric Surveying
7. Total Station Surveying etc.
1. Chain Surveying
 Chain surveying is defined as the type of surveying in which, only linear
measurements are taken with the help of chain (or) tape, without any angle
measuring instruments.
 Chain triangulation for a small area IS carried out by dividing the area into number
of triangles, whose sides should be easily measurable by using the chains.
2. Compass Surveying
 Compass survey is defined as the angle measuring technique with the help of a
compass, works on the principle that, a freely suspended magnetic needle points in
the magnetic north-south the direction.
 With the help of the chains (or) tapes, compass surveys are used to survey the
given area by various methods such as triangulation, traversing, etc.

8. 3. Plane Table Surveying
 Plane table surveying is a surveying method, in which a drawing board (plane
table) with accessories is used to survey and plot the ground instantaneously.
4. Level Surveying (or) Levelling
 The process of measuring the heights and relative heights of the points on (or)
above (or) below the surface earth is called levelling.
 This type of surveying deals with the measurements in the vertical plane.
5. Theodolite Surveying
 Theodolite is an instrument used to measure both horizontal and vertical angles
and theodolite surveying is defined as the surveying technique in which the
horizontal angles, vertical angles and their relative heights are measured by using
theodolites.
 Theodolite surveying is a very common method for all kinds of survey work
6. Tacheometric Surveying
 Tacheometric (or Tachometric) Surveying is the technique or method of surveying
in which, the horizontal distance can be calculated by using a special type of
theodolite (called tacheometer), without the direct measurement of distances.
 It is based on the principle of Stadia Surveying.
7. Total Station Surveying etc.
 Total station is a modem surveying instrument and it is a combination of an
electronics theodolite and an Electromagnetic Distance Meter (EDM).
 A total Station eliminates all other surveying instruments, having the advantages
of all other surveying instruments.

9. Types of Surveying Operations:

The practice of surveying actually boils down to fieldwork and office work. The
FIELDWORK consists of taking measurements, collecting engineering data, and testing
materials. The OFFICE WORK includes taking care of the computation and drawing
the necessary information for the purpose of the survey.

FIELDWORK

FIELDWORK is of primary importance in all types of surveys. To be a skilled surveyor,
you must spend a certain amount of time in the field to acquire needed experience. A
high degree of proficiency in actual surveying, as in other professions, depends largely
upon the duration, extent, and variation of the actual experience.

The Fieldwork consists of the following operational skills
 STUDYING the problem thoroughly before going into the field. The Surveyor
should know exactly what is to be done, how to do it and what instruments and
materials are needed to accomplish the project.
 It is essential that the surveyor should develop SPEED and CONSISTENT
ACCURACY in all fieldwork. This means that the surveyor needs practice in
handling the instruments, taking observations and keeping field notes, and
planning systematic moves.
 It is important that the surveyor also develop the habit of CORRECTNESS.
Surveyor should not accept any measurement as correct without verification.
Verification, as much as possible, should be different from the original method
used in measurement.
 Fieldwork also includes adjusting the instruments and caring for field equipment.
Do not attempt to adjust any instrument unless you understand the workings or
functions of its parts.

Factors Affecting Fieldwork
 The surveyor must constantly be alert to the different conditions encountered in
the field. Physical factors, such as TERRAIN AND WEATHER CONDITIONS,
affect each field survey in varying degrees.
 Measurements using telescopes can be stopped by fog or mist. Swamps and flood
plains under high water can impede taping surveys. Sights over open water or
fields of flat, unbroken terrain create ambiguities in measurements using
microwave equipment. The lengths of light-wave distance in measurements are
reduced in bright sunlight
 The STATE OF PERSONNEL TECHNICAL READINESS is another factor
affecting field-work. As the surveyor gain experience in handling various
surveying instruments, it can shorten survey time and avoid errors that would
require resurvey.

10.  The PURPOSE AND TYPE OF SURVEY are primary factors in determining the
accuracy requirements. In some construction surveys, normally inaccessible
distances must be computed. The distance is computed by means of trigonometry,
using the angles and the one distance that can be measured. The measurements
must be made to a high degree of precision to maintain accuracy in the computed
distance.
Survey speed is not the result of hurrying; it is the result of saving time through the
following factors:
1. The skill of the surveyor in handling the instruments
2. The intelligent planning and preparation of the work
3. The process of making only those measurements that is consistent with the accuracy.

Office Work
OFFICE WORK in surveying consists of converting the field measurements into a usable
format. The conversion of computed, often mathematical, values may be required
immediately to continue the work, or it may be delayed until a series of field
measurements is completed. Although these operations are performed in the field during
lapses between measurements, they can also be considered office work. Such operations
are normally done to save time. Special equipment, such as calculators, conversion tables,
and some drafting equipment, are used in most office work. In office work, converting
field measurements (also called reducing) involves the process of computing, adjusting,
and applying a standard rule to numerical values.

(a) Computation
In any field survey operation, measurements are derived by the application of some form
of mathematical computation. It may be simple addition of several full lengths and a
partial tape length to record a total linear distance between two points.
Office computing converts these distances, elevations, and angles into a more usable
form. In general, office computing reduces the field notes to either a tabular or graphic
form for a permanent record or for continuation of fieldwork.

(b) Adjustment
Some survey processes are not complete until measurements are within usable limits or
until corrections have been applied to these measurements to distribute accumulated
errors. Small errors that are not apparent in individual measurements can accumulate to a
sizeable amount.
Adjusting is the process used to distribute these errors among the many points or stations
until the effect on each point has been reduced to the degree that all measurements are
within usable limits.

(c) Significant Figures
In a measured quantity, the number of significant figures is determined by the accuracy
of the measurement. In surveying, the significant figures should reflect the allowable

11. error or tolerance in the measurements. The number of significant figures in a number
ending in one or more zeros is unknown unless more information is given.
When decimals are used, the number of significant figures is not always the number of
digits. A zero may or may not be significant, depending on its position with respect to the
decimal and the digits. As mentioned above, zeros may have been added to show the
position of the decimal point. Study the following examples:
0.000047 .................. two significant figures
0.0100470 .................. six significant figures
0.1000470 .................. seven significant figures
2.0100470 .................. eight significant figures
In long computations, the values are carried out to one more digit than required in the
result. The number is rounded off to the required numbers of digits as a final step.

(d) Rounding Off Numbers
Rounding off is the process of dropping one or more digits and replacing them with
zeros, if necessary, to indicate the number of significant figures. Numbers used in
surveying are rounded off according to the following rules:
1. When the digit to be dropped is less than 5, the number is written without the digit or
any others that follow it.
(Example: 0.054 becomes 0.05.)
2. When the digit is equal to 5, the nearest EVEN number is substituted for the preceding
digit. (Examples: 0.055
becomes 0.06; 0.045 becomes 0.04.)
3. When the digit to be dropped is greater than 5, the preceding digit is increased by one.
(Example: 0.047 becomes 0.05.)
4. Dropped digits to the left of the decimal point are replaced by zeros.
5. Dropped digits to the right of the decimal points are never replaced.

(e) Checking Computations
Most mathematical problems can be solved by more than one method. To check a set of
computations, we should use a method that differs from the original method, if possible.
An inverse solution, starting with the computed value and solving for the field data, is
one possibility. The planimeter and the protractor are also used for approximate checking.
A graphical solution can be used, when feasible, especially if it takes less time than a
mathematical or logarithmic solution.

Chains
The most common and accurate method is the method, of measuring linear
distance with, a chain or tape, called chaining. For a routine work and accuracy a metallic
chain is used. Where a more accurate work has to be carried out a steel tape is used. The
term chaining is used for distance measurement both by chain or tape.

12. Chains are formed of straight links of galvanized mild steel wire bent into rings.
Brass handles are provided at each end. These handles are connected through a swivel
joint so that the chain can be turned round without twisting. The length of each link is
from the centre of the middle ring on either side of it. The length of the first link is
inclusive of the length of the handle.
Metric chain
 Metric chains are available in lengths of 20m and 30 m.
 The 20 m chain is divided into 100 links (each of 0.2 m) with tallies connected at
every 10 links (i.e., at 2 m intervals).
 This chain can be used on fairly level ground.
 The 30 m chain is divided into 150 links with each link of 0.2 m length.
 Tallies are provided after every 25 links (i.e., 5 m length).
 After every meter a brass ring is attached.
 The chain is heavy and suitable for Use on level ground.

Engineer's chain
 This chain is 100 ft in length and divided into J 00 links.
 The details of construction are the same as that of the metric chain.
 For every ten links brass tags are provided.
 This type of chain is used in countries where FPS system is still used.
Gunter's chain
 This chain is 66 ft of length with 100 links of 0.66 ft long.

13.  It is very convenient to measure distances in miles and furlongs.
 Also it is used for measuring land where the unit of area is an acre.



Band chain
Band chain, also called as steel band, is a ribbon of steel with brass swivel at each end.
It is 20 to 30 m in length and 16 mm wide.
It is wound on an open steel cross or in a metal real in a closed case.
The graduations are marked on the steel ribbon as follows: (i) brass studs divide the band
at every 0.2 m and numbered at every I m. (ii) the first and the last links are subdivided
into mm and mm, (iii) etched graduation are provided in meters, decimeters and
centimeters on one side and 0.2 m links on the other, (iv) brass tallies are provided at
every 5 m length of the band.

14. Tapes
Tapes are made of different materials and used for accurate measurements. They are
divided into five classes. Viz.,
i. Cloth or linen tape
ii. Metallic tape
iii. Hi- steel tape
iv. Invar tape and
v. Synthetic material tape
(i) Linen (or) Cloth tape
 Linen tapes are closely woven linen and varnished to resist the moisture.
 The width of the linen tape varies from 12 mm to 15, mm.
 The length of the tape varies from 10 m to 30 m.
 One of the tapes is fitted with a ring and the ring length is included in the total
length.
 It is not suitable for accurate survey work and can only be used for ordinary
works.
(ii) Metallic tape
 The tape, reinforced with brass (or) copper wires in order to prevent the stretching
or twisting of the fibres of the tape is called the metallic tape.
 Metallic tapes are available in 10 m, 20 m, 30 m, 50 m and 100 m.
 Generally metallic and steel tapes are used for measuring the accurate
measurements.
(iii)Steel tapes
 It consist of a light strip of width 6 mm to 10 mm are accurately graduated.
 Steel tapes are available in 1 m, 2 m, 3 m, 5 m, 10 m, 15 m, 20 m, 30 m and 50 m
lengths. Steel tapes are not suitable for terrain with vegetation (or) rocky grounds.
(iv)Invar tape
 Invar tapes are made of an alloy of Nickel and Steel of 36% and 64% respectively,
having very low coefficient of thermal expansion.

15.  The width of the invar tapes is 6 mm. It is available in 10m, 50 m and 100 m.
 Invar tapes are suitable for the survey works with highest accuracy.
Disadvantages of Invar Tapes
Following are the disadvantages of invar tapes
1. It develops creep with time
2. It requires more persons to stretch and handle
3. More expensive, easily get deformed etc.

Ranging

When a survey line is longer than a chain length, it is necessary to align
intermediate points on chain line so that the measurements are along the line. The
process of locating intermediate points on survey line is known as ranging. There
are two methods of ranging viz., direct ranging and reciprocal ranging.

Direct Ranging

If the first and last points are intervisible this method is possible. Figure shows the
intervisible stations A and B in which an intermediate point C is to be located.
Point C is selected at a distance slightly less than a chain length. At points A and B
ranging rods are fixed. The assistant holds another ranging rod near C. Surveyor
positions himself approximately 2 m behind station A and looking along line AB
directs the assistant to move at right angles to the line AB till he aligns the ranging
rod along AB. Then surveyor instructs the assistant to mark that point and stretch
the chain along AC.

Indirect or Reciprocal Ranging

Due to intervening ground, if the ranging rod at B is not visible from station A,
reciprocal ranging may be resorted. Figure shows this scheme of ranging. It needs
two assistants one at point M and another at point N, where from those points both
station A and station B are visible. It needs one surveyor at A and another at B. To
start with M and N are approximately selected, say M1 and N1. Then surveyor
near end A ranges person near M to position M2 such that AM2N1 are in a line.
Then surveyor at B directs person at N, to move to N2 such that BN2M2 are in a
line. The process is repeated till.

16. AMNB are in a line.
Fig. 1.6 Direct & Indirect Ranging