Basic Surveying Chapter 1: Introduction

CHAPTER One

INTRODUCTION:

Table of contents:
Page No.

1.1. Definition……………………………………………………………………………………………………..2
1.2. Need for Surveying……………………………………………………………………………………..3
1.3. Types and Principles of Surveying………………………………………………………………3
1.4. Sources of Error Precision and Correction………………………………………………….6

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Basic Surveying Chapter 1: Introduction

1.1 Definition:

Surveying:-is defined as an art of making measurements of the relative position of

natural and man-made features on the earth’s surface and display the information
either graphically or numerically.

In order to gain a clear understanding of the procedures for making surveying

measurements on earth’s surface, it is necessary to be familiar with the meanings of
certain basic terms.

Vertical line: - at any point on the earth’s surface is the line that follows the
direction of gravity at a point. At a point there is only one (single) vertical line.

Vertical plane: - at a point is any plane that contains the vertical line at the point.
There are unlimited numbers of vertical planes at a given point.

Horizontal line: - It a point is any line that is perpendicular to the vertical line at
that point. At a point there are an unlimited number of horizontal lines.

Horizontal plane: - at a point is the line that is perpendicular to the vertical line at
the point. There is only one horizontal plane through a given point.

A vertical angle: - is an angle measured in a vertical plane.

A Horizontal angle: - is an angle measured in a horizontal plane between two

vertical planes.

Elevation of a point is its vertical distance above or below a given reference level
surface. The difference in elevation between two points is vertical distances between
two level surfaces contain the two points.

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Basic Surveying Chapter 1: Introduction

1.2 Need for surveying:

Though it is impossible to predict when surveying started it is possible to assume

surely that it was as old as early civilization. Because every type of construction
needs surveying as a prerequisite whatever may be its type.

All types of engineers, as well as architects, foresters, and hydrologists, are

concerned with surveying as a means of planning and laying out their projects,
surveying is needed for subdivisions, buildings, bridges, highways, railroads canals,
piers, wharves, dams, irrigation and drainage networks, and many other projects. In
addition it is required for lying out of industrial equipment setting machinery, holding
tolerances in ships and air lines, preparing forestry and geological maps.

1.3 Types and principles of surveying:

In general surveying is divided into two broad classes as geodetic and plane
surveying

Geodetic surveying:

The study of size and shape of the earth and its gravity field is known as geodesy.
Therefore, geodetic surveying is a type of surveying in which the curvature of the
earth is considered. Large areas of the earth’s surface are involved and it requires
high degree of precisions. Satellite positioning system, which can obtain the three-
dimensional coordinates of any point, is considered in this method.

Plane Surveying:

A type of surveying in which the curvature of the earth is considered and relatively
small areas are under considers and, assumed that the earth’s surface is flat, i.e. it
gives a horizontal plane. Measurements plotted will represent the projection on the
horizontal plane of the actual field measurements. For example if the distance
between two points A and B on a hill side is cos , where is the angle that line
AB makes with the horizontal assuming uniform slope.

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Basic Surveying Chapter 1: Introduction

Classification of surveying based on purpose:

Most of these types of survey are planning type surveying.

1. Control survey: - is a survey made to establish the horizontal or vertical

positions of an arbitrary point.
2. Topographic Survey is a survey conducted to determine the configuration
of the ground and all the features on it (man made or natural)
3. Construction Survey: - Surveys performed to locate or layout engineering
works.
4. Cadastral Survey: - us a survey made to determine the lengths and
directions of boundary lines and the area of the tract bounded by these lines.
Or it is simply a survey made to establish the positions of boundary lines on
the ground.
5. Hydrographic Survey: - is a survey conducted to determine the
configuration of the bottom of the body of water.
6. Route Survey: - involves the determination of the relief and the location of
natural and artificial objects along a proposed route for high– way, railroad,
canal, pipeline, power line or other utilities. The may also involve the
calculation of earthwork quantities.
7. Arial survey (or photogram metric survey): - a survey conducted by
means of Arial photography.

Basic Principle:

For an area or land to be surveyed, it is always possible to choose two points and to
measure the distance between them. Say base line AB was dawn on paper to scale.
Other points can now be located relative to this line by taking two other
measurements and drawing them to scale.

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 Basic Surveying Chapter 1: Introduction

Different methods can be applied in locating the other points, these are:

1. Horizontal plane:

a-Inter section by distance (Trilateriation)

C - Measure Ac and BC and C can be located

A B

b- Intersection by angles (triangulation)

C -Measure <ABC and <BAC then C can be located

A B

c- Angel and distance method (Traversing)

-Measure BC and angle ABC

C Then C can be located

A B

d -Off set method B

-AD is known measure
CD at right angel to AB
90o
D C

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Basic Surveying Chapter 1: Introduction

2. Vertical plane:

A - Ordinary leveling:

In this method the difference of elevations b/n two points is determined using Level
and leveling staff.

B. Trigonometric leveling:
The difference in elevations between two points can be determined by measuring the
vertical angle of the line from one point to the other and then computing the
difference in elevation from the knowledge of the slope distance or horizontal
distance between two points.

C. Barometric leveling for preliminary survey not accurate.

1.4. Sources of Error precision and correction:

Errors and Mistakes:

No one is perfect in mature while measuring any quantity and there are no perfect
instrument with which to do the measuring. Thus the results of all measurements
are imperfect and this imperfectness is the results of errors and/or mistakes

Errors: - are inaccuracies in measurement caused by the types of equipment used

for by the way in which the equipments are used. In other words it is the difference
from the true value due to personal or instrumental imperfectness.

Errors cannot be eliminated but they can be minimized to some degree by careful
work combined with the application of certain numerical corrections.

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Basic Surveying Chapter 1: Introduction

Mistakes: - (or blunders) are inaccuracies in measurement occurring because of

some part of the surveying operation are performed improperly (i.e. carelessness of
the survey or). They are the difference from the true value caused by the inattention
of the survey or for example, he may read a number as I when it is actually and
record the wrong quantity.

Mistakes are also known as gross error and can be eliminated by adopting standard
methods of observation, booting and checking. They are random in nature.

Sources of error:

In general there are three sources of error: people, instruments and nature. So,
from this point of view the sources of error may be summarized as follows.

1. Personal Errors: - cased by the inability of the individual to make exact

observation due to the limitations of human sight, touch and hearing. For
example in estimating the fractional part of a scale of person cannot read it
perfectly and the reading will always be either a little large or a little small.

2. Instrumental Errors: - Occur because of imperfect production of parts of

the instrument cannot be adjusted exactly with respect to each other. More
over with time the wear and tear of the instrument cause errors. These can
be minimized or even eliminated by proper design and adjustment of
instrument.

3. Natural Errors: - Caused by the variations in one or more of the natural

variables like temperature, wind, moisture, magnetic variations and so on.

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Basic Surveying Chapter 1: Introduction

Types of errors:
Errors are said to be systematic or accidental based on their occurrence and sources

1. Systematic Error; -are also known as cumulative error. These arise from the
methods of measurements, the instruments used and the physical conditions at
the time of measurement must all be considered in the respect.
Expansion of steel tapes, frequency changes in electromagnetic distance
measure (EDM) instruments and collimation in a level are jest few examples of
possible sources of systematic errors. Though they are cumulative in nature
some of them can be eliminated and some and some may be minimized.

2. Accidental Errors: - (Random Errors) they are excess of systematic errors.

They are beyond the control of the observer and are random in nature.

Accuracy and Precision:

As discussed earlier any measurement cannot exactly be perfect, due to errors

or/and mistakes. Hence a major concern of in surveying is the precision of the work
and the objective of the survey or is to make measurements that are both precise
and accurate. The terms accuracy and precision are constantly used in surveying &
yet their correct meanings are a little difficult to grasp.

Accuracy denotes the closeness of a given measurement to the true value. It is the
degree of perfection achieved in measurement.

Precision or apparent accuracy is the degree of closeness to another measurement of

the same quality. If a quality is measured several times and the value obtained are
very close to one another might not close to the true value.

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Basic Surveying Chapter 1: Introduction

Example 1.1:

Consider the case with which two parties record the length of a line
having 50.357m.

1st team: 50.37m, 50.36m, 50.355m…………Avg. = 50.362m

2nd team: 50.355m, 50.356mm, 50.358m …… Avg. = 50.356m

From the above results one can conclude the following

The first team is more accurate but less precise and second team is less
accurate but more precise. Therefore a measurement that is precise will always
be accurate if it contains no errors.

In measuring distance precision is defined as the ratio of the error of the

measurement to the distance measured and it is reduced to fraction having a
numerator of unity.

Example 1.2:

If the distance of 210m is measured and the error is later estimated to equal 0.35m,
the precision of measurement is 0.35/210 = 1/ 600. This means for every 600m
measurement there is an error of 1m if the work were done with same degree of
precision.

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