Definition of Surveying

Surveying is defined as the science of making measurements of the

earth specifically the surface of the earth. This is being carried out by

finding the spatial location (relative / absolute) of points on or near the

surface of the earth.

Different methods and instruments are being used TO facilitate the

work of surveying.

The primary aims of field surveying are :

• To measure the Horizontal Distance between points.

• To measure the Vertical elevation between points.

• To find out the Relative direction of lines by measuring horizontal

angles with reference To any arbitrary direction and

• To find out Absolute direction by measuring horizontal

angles with reference To a fixed direction.

These parameters are utilized To find out the relative or absolute

coordinates of a point / location.

Importance of Surveying TO Civil Engineers

The planning and design of all Civil Engineering projects such as

construction of highways, bridges, tunnels, dams etc are based upon

surveying measurements.

Moreover, during execution, project of any magnitude is

constructed along the lines and points established by surveying.

Thus, surveying is a basic requirement for all Civil Engineering

projects.

Other principal works in which surveying is primarily utilised are

• To fix the national and state boundaries;

• To chart coastlines, navigable streams and lakes;

• To establish control points;

• To execute hydrographic and oceanographic charting and

mapping; and

• To prepare Topographic map of land surface of the earth.

Objectives of Surveying

• To collect field data;

• To prepare plan or map of the area surveyed;

• To analyse and To calculate the field parameters for setting out

operation of actual engineering works.

• To set out field parameters at the site for further engineering

works.

Plan: Orthographic representation of features on or near the

surface of the earth in Large Scale on a horizontal plane.

Map: Graphical representation of features on or near the surface of

the earth in small scale on a horizontal plane and is constructed using

a projection system other than orthographic.

Divisions of Surveying

The approximate shape of the earth can best be defined as

an oblate tri-axial ovaloid. But, most of the civil engineering works,

concern only with a small portion of the earth which seems TO be a

plane surface. Thus, based upon the consideration of the shape of the

earth, surveying is broadly divided into two types.

Geodetic Surveying

Plane Surveying

Oblate (spheroid): An oblate (spheroid) is a surface of revolution

obtained by rotating an ellipse about its minor axis i.e., having

equatorial radius greater than the polar radius.

Ovaloid: A pear shaped figure having dimension of one hemisphere

larger than the other for earth, southern hemisphere is larger than the

northern.

Geodetic Surveying

In this branch of surveying, the true shape of the earth is taken

into consideration.

This type of surveying is being carried out for highly precise work

and is adopted for surveying of large area.

Plane Surveying

In this method of surveying, the mean surface of the earth is

considered to be a plane surface. This type of survey is applicable

for small area (less than 200 square kilometer). Thus for most of the

Civil Engineering projects, methods of plane surveying are valid.

This course is restricted to the different aspects of plane

surveying. Henceforth, in this course work, the word surveying

implies plane surveying.

Fundamental assumptions in Plane surveying

• All distances and directions are horizontal;

• The direction of the plumb line is same at all points within the

limits of the survey;

• All angles (both horizontal and vertical) are plane angles;

• Elevations are with reference to a datum.

Plumb line: The direction of the lines of force of earth's gravity

field. In field surveying, it is defined by the direction of a freely

suspended plumb-bob

Elevation: The vertical distance of a point from a datum.

Datum: A leveled surface taken as reference for the determination

of elevations of points.

Classifications of Surveying

Based on the purpose (for which surveying is being conducted),

Surveying has been classified into:

• Control surveying: To establish horizontal and vertical positions

of control points.

• Land surveying: To determine the boundaries and areas of

parcels of land, also known as property survey, boundary survey or

cadastral survey.

• Topographic survey: To prepare a plan/ map of a region which

includes natural as well as and man-made features including

elevation?

• Engineering survey: To collect requisite data for planning,

design and execution of engineering projects. Three broad steps are

1) Reconnaissance survey: To explore site conditions and

availability of infrastructures.

2) Preliminary survey: To collect adequate data To prepare

plan / map of area To be used for planning and design.

3) Location survey: To set out work on the ground for actual

construction / execution of the project.

• Route survey: To plan, design, and laying out of route such as

highways, railways, canals, pipelines, and other linear projects.

• Construction surveys: Surveys which are required for

establishment of points, lines, grades, and for staking out

engineering works (after the plans have been prepared and the

structural design has been done).

• Astronomic surveys: To determine the latitude, longitude (of the

observation station) and azimuth (of a line through observation

station) from astronomical observation.

• Mine surveys: To carry out surveying specific for opencast and

underground mining purposes.

Principles of Surveying

The fundamental principles upon which the surveying is being

carried out are

Working from whole To part.

After deciding the position of any point, its reference must

be kept from at least two permanent objects or stations whose

positions have already been well defined.

The purpose of working from whole To part is

To localize the errors and

To control the accumulation of errors.

This is being achieved by establishing a hierarchy of networks

of control points. The less precise networks are established within

the higher precise network and thus restrict the errors. To minimize

the error limit, highest precise network (primary network) Figure

1.1 of control are established using the most accurate / precise

instruments for collection of data and rigorous methods of analysis

are employed To find network parameters. This also involves most

skilled manpower and costly resources which are rare and cost

intensive. Further elaboration has been done in Lesson 3 under

"Overview of Land Surveying".

Control points: Stations having known position.

.

he reference of any point, say X, has TO kept with respect TO, at

least, two permanent objects or well defined points, say Y and Z.

Generally, this has been achieved by taking measurement of two

parameters. The location of a point, say X can be done as shown in

the figure below.

(a) Distances YX and ZX (Figure 1.2)

(b) Perpendicular distance OX and distance OY or OZ (Figure 1.3)

(c) Distance YX or ZX and angle YZX or ZYX (Figure 1.4(a))and

(Figure 1.4(b))

(d) Angles YZX and ZYX. (Figure 1.5)

The point of intersection of the two measured parameters defines

the position of the point.

Operations in Surveying

Operations in surveying consists of :

Planning

Field Observation

Office Works

Setting out Works

Planning

To decide

• the methods To be adopted for surveying;

• the resources (instruments & personnel) To be used;

• The control points / stations To be used (those already available

and/ or To set up).

The planning operation needs a-priori field visit and this is known

as reconnaissance.

Field Observation

It involves

• Collection of field data by making necessary measurements;

• Recording of observed data in a systematic manner.

Before starting any field observation, the permanent adjustments of

all the instruments need TO be checked thoroughly by trained

personnel and if required, it must be adjusted.

Office Work

It involves

• Processing, analysing and calculation of observed data;

• Preparation of necessary data (for making plan or map of the

area);

• Making of a plan or map of the area;

• Computation of relevant field parameters as per design for setting

out engineering works at site.

Setting out Works

To locate and establish different parameters / dimensions at the

site as per design for further engineering works.

Mapping Fundamentals

The data collected through field surveying are presented in the

form of a plan or a map.

Since, the actual surface of the earth is curved, and the surface of

the map is flat, a method of projection is usually used To fit a curved

surface of earth into a plane surface of paper. However, no map can

represent a terrain without some distortion. To minimize the effect of

distortion, conformal projections are generally employed.

To prepare a map, first a grid of meridians and parallels of latitude

is being prepared To provide a framework of map. Control points are

then plotted by their spherical coordinates (latitude, longitude). A

plane coordinate system is then used To plot other points accurately

in orthogonal coordinate system obviating direct use of spherical

coordinates.

In case of plane surveying, the earth's surface is regarded as plane

and thus, a map is constructed by orthographic projection. Points are

being plotted by their rectangular coordinates, angles and distances

as horizontal.

During the preparation of maps, the factors which need important

considerations are:

• Scales

• Conventional symbols

• Generalization of details

• Plotting accuracy

• Rectangular Coordinates

Scales

The selection of scale is one of the most important considerations

during mapping. It is decided on the basis of :

• purpose of the map;

• nature of terrain To be mapped;

• the size of the final sheet;

• Availability of resources To get it prepared and printed.

Some of these factors are of opposite and conflicting in nature.

Therefore, in selecting the scale, the map-maker has To make a

judicious decision and To make a compromise.

Table 2.1 Suggested scales for different types of survey

Serial No Purpose of Survey Scale R.F.

1. Land Survey 1 cm = 5 m TO 50 m 1:500 TO 1:5000

2. Topographical Survey 1 cm = 0.25 km TO 2.5 km 1:25,000 TO 1:250,000

3. Building Site 1 cm = 10 m 1:1000

4. Route Survey 1 cm = 100 m 1:10,000

5. Town Planning 1 cm = 100 m 1:10,000

Conventional Symbols

After the selection of scale of plotting, the map preparation should

be carried out in such a way that it becomes intelligible. It conveys

useful meaning TO the reader only when one can identify the ground

features identical with those shown on the map. In India, conventional

symbols, proposed by Survey of India, are used To depict objects on

map. Symbols generally used for preparation of Topographical map are

shown in Figure 2.1.

Figure 2.1 Standard (Survey of India) Conventional Signs of Salient

objects for Topographic Map

Symbol Description Symbol Description

Village (open)

Telephone Line

Church

Electric Power Line

Temple

Railway,Broad Gauge

Double Line

Mosque

Bridge carrying Railway

over Road

Idgah

Metalled Road

Burial-Ground

National Highway

Boundary pillar

UN-Metalled Road

Aerodrome

Level Crossing

Well

Foot Path with

Bridge,Culvert

Swamp or Marsh with Cultivation

( Road or Railway )

Embankment

Lake with

a)Defined Limit

b)Fluctuating Limit

c)Embankment

Orchard / Garden /

Plantation

Single Line Stream

a) Perennial

b) Non-Perennial

Trees

a) Scattered

b) Surveyed

Canal with Navigation Lock and

Road

Bench Mark

Aqueduct with Road Alongside

Triangulation Station

Earthwork Dam

Broken or Rocky Ground

Masonry dam with Road

ConTOurs

Map Generalization

Since a map represents earth's surface in a small scale, it cannot

depict all the objects present on the surface of earth. However, it is

essential To show the important details and weed out the trivials.

The process involved in selecting the essential details from the

multitude of Topographical objects and representing them in a

specified manner is called ‘generalization'. It serves the purpose of

facilitating the production of a legible homogenous map.

Moreover, when the representation of an important object / feature

is done by its conventional sign, it occupies more space on the map

sheet than what the scale permits. This space occupied by the

conventional sign may require cutting down of some other details

known as “generalization of details” on maps. A Topographical map or

even a large scale engineering survey map therefore may not contain

all the details as actually present on the surface of the earth, as its

scale does not permit the same.

The salient points required for generalization are:

• Choice of object / features in connection with its purpose and the

scale of map.

• Elimination of terrain details that cannot be maintained because

of legibility and clarity in the map.

• Simplification of the form of terrain details that cannot be omitted

but of which a detailed representation would interfere with the image

of the map.

Plotting Accuracy

The precision of a map / plan depends on the fineness and

accuracy with which the details are plotted. Moreover, the plotting

accuracy on paper, varies between 0. 1 mm TO 0.4 mm, of which the

mean value of 0.25 mm is usually adopted as plotting accuracy. This,

therefore, imposes limit on linear measurements that can be

represented on the map at a given scale and thus accuracy. The

measurements TO be made on the ground. For example, if the

plotting scale is 1: 1000, than the maximum possible distance on

ground that can be represented as map is 0.25 x 1,000 mm i.e., 0.25

meter. Thus, any detail having length less than 0.25 meter cannot be

plotted and thus, field measurement for objects having dimensioned

less than 0.25 meter are not needed. If the scale is still smaller say

1: 50,000, then maximum plottable ground distance is 0.25 x

50,000mm i.e., 12.5 meter. Thus any object having length or width

less than 12.5 meter, such as roads, railway track, etc. cannot be

plotted on map. However, if the features are important and cannot be

ignored, these are represented on map by proper conventional signs

and colours adopting the ‘Principles of Generalization' of Details.

Rectangular Coordinates

Large scale maps of plane surveying are generally prepared by

means of a system of rectangular coordinates with two reference

axes representing the east-west and north-south directions

respectively in horizontal and vertical directions. In order TO make

the individual surveys related TO common system and make the data

useful for multi-purpose cadastral survey, at least one station

(Control point) within the area of survey should be designated by a

pair of coordinates in the National coordinate system. This is

significant as the point such described is unique within the system.

For India, Survey of India defined the National rectangular coordinate

system with origin at Kalianpur (24°07', 77°39'), Madhya Pradesh.

Examples

Ex2-1 In a plan, a 10 cm scale drawn shrunks TO 9.7 cm. If the

scale of the given plan is written as 1:250, determine the actual

length of a line which at present shows 10 cm.

Solution :

Present representative fraction (R.F.) =

Therefore Actual distance = = 25.77 m

Overview of Land Surveying

The fundamental objective of land surveying is TO prepare

a plan or map of an area. The map thus prepared serves as the

primary source of information about the surface of the earth for

further engineering works. The data required for making of a map

gets collected through field surveying. TO start field surveying, it is

required TO know very accurately, the geographical coordinates

(latitude, longitude) of at least one point, known as control point and

the length as well as azimuth of a line, known as baseline(Figure 3.1).

The Latitude of the point and the azimuth of the line are determined

through astronomical survey and longitude from time measurement.

The length of the line is measured with a distance measuring

instrument.

From the control point in association with the base line, a number

of intervisible points are selected such that on joining these points

well shaped triangles are required TO be formed. These triangles

carry forward points whose geographical positions are calculated

from the measurements (horizontal distance, horizontal angles) taken

from the network of triangles. The calculated parameters undergo

further adjustment by satisfying the geometrical conditions

associated with the parameters as well as with figures. This helps in

minimisation of errors which may creep in further surveying

operation. Inside the big triangles formed by widely spaced control

points, network of smaller triangles get established (Figure 3.2). This

process gets repeated materializing the basic principle of surveying

"To work from whole To part". Thus the entire area TO be surveyed

gets covered with network of triangles.

The detail surveying is then carried out within the smallest

triangle. During surveying, measurements (distance, direction,

angles, height etc.) for important objects/ points are taken. The

measurements are then used for necessary calculations and

adjustments resulting in identification and finding positions (with

respect To standard reference) of salient objects.

To prepare map, first a grid of medians and parallels of latitudes

is being prepared To provide a frame work of map. Control points are

then plotted by their spherical coordinates.

Then objects are graphically represented in a rectangular

coordinate system for depicting planimetric position. Terrain height

is depicted by using contours at regular interval. The identification of

objects is depicted using conventional symbols and colours Figure

2.1.

TO prepare map of the area, inside the marked area in Figure 3.3,

first the surveying measurements and plotting are being carried out

for plot number 1(Figure3.4).

Next, detail surveying (Figure3.5) and plotting are being carried

out for plot number 2 (Figure 3.6) and subsequently detail mapping is

carried out for plot number 3 and plot number 4. Then, a final map of

the whole area is being prepared by mosaicing the component maps

(Figure 3.7)

Indian Topographic Maps

Topographic maps provide the graphical portrayal of objects

present on the surface of the earth. These maps provide the

preliminary information about a terrain and thus very useful for

engineering works. For most part of India, Topographic maps are

available which are prepared by the Survey of India. TO identify a

map of a particular area, a map numbering system has been adopted

by Survey of India. The system of identification is as follows:

An International Series (within 4° N TO 40° N Latitude and 44° E

TO 124° E Longitude) at the scale of 1: 1,000,000 is being considered

as base map. The base map is divided into sections of 4° latitude x 4°

longitude and designated from 1 (at the extreme north-west) TO 136,

covering only land areas and leaving any 4° square if it falls

completely in the sea (Figure 3.8).

For Indian Topographic maps, each section is further divided into

16 sections (4 rows by 4 columns), each of 1° latitude x 1° longitude

(1:250,000), staring from a letter A (North-West corner) and ending on

P, column-wise. These degree sheets are designated by a number and

an alphabet such as 53 C (Figure 3.9).

These degree sheets are further sub-divided in the following ways:

Each sheet is divided into four parts (2 rows by 2 columns),, each

of 30' latitude x 30' longitude (1:100,000) designating them by cardinal

directions NW, NE, SW, and SE. Such sheets are identified as 53 M/SE

(Figure 3.10).

Degree sheets have also been divided into 16 sheets (4 rows by 4

columns), each 15' latitude x 15' longitude (1:50,000) and numbered

from 1 (at the north-west corner of the particular degree sheet) TO 16

column wise and are identified as 53 B/3 (Figure 3.11).

Each 1:50,000 scale sheets contain four (2 rows by 2 columns)

1:25,000 sheet (7’ 1/2 latitude x 7' 1/2 longitude) which are numbered

NW, NE, SW, and SE. Such sheets are identified as 53 O/14/NE (Figure

3.12).

In this way, the Topographic map of most of the area of India may

be acquired at the scale available and subsequently can be updated

and upgraded as required for a particular project. For large scale

maps, further surveying needs To carry out.