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GEOMATICS ENGINEERING / SURVEYING CHAPTER 1 Dr. Muhammad Ashraf Javid Assistant Professor Department of Civil and Environmental Engineering Email: [email protected] 1

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GEOMATICS ENGINEERING /

SURVEYING

CHAPTER 1

Dr. Muhammad Ashraf Javid

Assistant Professor

Department of Civil and Environmental Engineering

Email: [email protected]

1

Geomatics Engineering / Surveying

• Credit Hours (2+1) = 3.0

• Assessment policy

• Quizzes (10%)

• Assignments (10%) – 2 weeks will be given for each assignment

and late assignments will not be entertained for any reason.

• Lab. Work (20%)

• In-Semester exams (30%)

• Final exam (30%)

2

Course Description

• The course covers introduction to geomatics engineering,

distance measurement, leveling, angle measurement,

indirect distance measurement, topographic surveying

areas and volumes, construction surveying and road

curve preparation and practical.

3

Course Contents

• Introduction of Geomatics engineering

• Coordinate systems and scales

• Distance measurement

• Angle measurement and traversing

• Leveling

• Road curve design

• Area and earthworks calculation

• Construction and topographic surveying

4

Chapter 1 contents

• Introduction

• Role of surveying in civil engineering

• Classification of surveying

• Basic Principles of Surveying

• Coordinate systems

• Sources of Errors

5

Introduction to Geomatics Engineering

• Geomatics • It is the discipline of gathering, storing, processing, and delivering geographic

or spatial information.

• Surveying • The discipline encompassing all methods of gathering and processing

information about our physical earth and its environment. Or

• The art of making measurements of the relative positions of natural and man-made features on the Earth’s surface, and the presentation of this information either graphically or numerically.

• Geodesy • Geodesy is the discipline that deals with the measurements and representation

of the Earth, including its gravity field, in a three-dimensional time varying space.

Geodesy focus on the Earth and neglect any man-made features on it

(e.g. buildings, public utilities, etc.), while surveying use the results of

geodesy for positioning and mapping of these features.

6

The role of Surveying in Civil Engineering Practice Surveyors are needed: • to maintain the geometric order during the construction process

What is this?

Laying them in the appropriate geometry, outstanding structures

can be created!

Wrong geometry – the structure is not functional!

• to provide fundamental data for the design and planning process

• to provide quantity control during the construction process (for example: earthwork quantities)

• to monitor the structure after the construction ( deformations, etc.)

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Surveying activities during the construction process

Before Construction Under construction After construction

Planning and data collection

Observations in the field

Processing the observations

(office)

Drawing maps, plans or providing

numerical data

Presenting documentation

to the client

Setting out on each phase

of construction

Field checks of construction

Providing data and services to

the client

Final (as-built) plan or map

on the construction

Presenting documentation

to the client

The role of Surveying in Civil Engineering Practice

Deformation Monitoring/ Load Tests

8

Primary Classification of Surveying

According to the space involved:

• Relatively small areas (Generally areas < 250 Km2)

• Surface of earth can supposed to be flat

• Measurements plotted represent a horizontal projection of the actual field measurements

•All Z dimensions are referenced to the mean surface of the earth or MSL

Pla

ne S

urv

eyin

g

•Plane surface

•Plane triangle

•Plane angles

• most engineering and property surveys are classed as plane surveys, although some route surveys that cover long distances (e.g., highways and railways) will have corrections applied at regular intervals.

9

Primary Classification of Surveying G

eodetic

Surv

eyin

g

• Large areas

• Surface of the Earth can not supposed to be flat

• The curvature of the Earth is taken into account

Mostly used for establishing control networks, determining the size and shape of the Earth and determining the gravity field of the Earth.

Don’t forget! Size does matter!

•Curved line

•Spherical triangle

•Spherical angles

10

Secondary Classification of Surveying

• Based on instruments

• ………………….

• Based on methods

• Triangulation surveying

• Traverse surveying

• Based on object

• Geological surveying

• Mine surveying

• Archeological surveying

• Military surveying

• Based on nature of field

• Land surveying

• Marine surveying

• Astronomical surveying

11

Secondary Classification of Surveying Types of Land Surveying • Cadastral Surveying

• Boundary surveying (conducted to determine the boundaries of fields, houses)

• Construction Surveying • Engineering surveys (done to prepare detailed drawings of projects)

• Topographic Surveying • Ground-based mapping (done to determine natural features)

• City Surveying • Carried out to locate the premises, streets, water supply and sanitary systems

• Hydrographic Surveying • Involving water bodies

• Geodetic Surveying • Locating points in space

• Photogrammetric Surveying • Aerial surveys

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Surveying Classification

Topographical Survey Topographical survey is concerned with the measurement of natural

and artificial features of the earth’s surface in order that a map of these features may be drawn and printed. The methods are similar to geodetic methods but are carried out to a lower order of accuracy.

Cadastral Surveying

It is the process of defining, demarcating, measuring and recording the boundaries of properties. Where these boundaries are formed by physical features, it overlaps with topographical surveying. As a general rule, cadastral work is done at larger scales than topographical mapping

Engineering or Construction Surveys

Engineering Surveys are those conducted with the special object of supplying particular information for engineering projects. They are usually at larger scales than topographical maps, but the methods used are often similar. Sometimes a high order of accuracy is required, for example, the measuring of a gap for a bridge.

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Basic Principles of Surveying

1. To work from whole to the part

• Whole area is first enclosed by main stations (i.e. controlling stations) and

main survey lines (i.e. controlling lines)

• Then area is divided into parts by forming well-conditioned triangles

• Main survey lines are measured very accurately and then the sides of the

triangles are measured.

• Main purpose is to avoid accumulation of error in measurements.

2. To locate a new station by at least two measurements (linear

or angular) from fixed reference points.

• Linear measurements refer to horizontal distances

• Angular measurements refer to the magnetic bearing or horizontal angle

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Basic Principles of Surveying

15

Basic Principles of Surveying

The positioning is usually separated into horizontal (2D) and vertical (1D) positioning.

Nowadays 3D positioning can

be achieved using satellite techniques, too.

How to achieve this?

Recall the definition of Surveying:

The art of making measurements of the relative positions of natural and man-made features on the Earth’s surface, and the presentation of this information either graphically or numerically.

Let’s determine the position (XP, YP) of point P!

Absolute vs Relative positioning

A

B

X

Y

ABl

(XA,YA)

(XB,YB)

P

XP

YP

dBP

dAP

Control points (known coords; marked on the field)

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Basic Principles of Surveying

Let’s determine the position of a third, unknown point (P).

We have two unknowns: XP, YP

We need two measurements:

• two distances

• one distance and an angle

• two angles

A

B

X

Y

(XA,YA)

(XB,YB)

P

dBP

dAP

dAP

a

a

b

a

b

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Basic Principles of Surveying

Fig. 1 Fig. 2 Fig. 3

b

A B A B A B

C C C

Unknown point Unknown point Unknown point

LAC? LBC? LAC?

θ1? θ2? θ1?

Known length AB Known length AB Known length AB

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Triangulation

• It is one of the methods of providing control in an area

which is to be surveyed

• It is based on the Trigonometric proposition that if one

side and three angles of a Triangle are known, the

remaining sides can be computed by the application of

Sine-Rule i.e.

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• Base Line AB is measured.

• Internal angles at A, B , C are measured.

A B

C

D

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Traverse • A traverse consists of a connected series of lines on earths’

surface, the length and bearings of which have been determined. Following measurements are made:-

a. Horizontal Angles

b. Vertical Angles

c. Distances

d. Bearings

A

E D

C

Traverse Stations

Traverse Legs

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Trilateration Trilateration methods involve the determination of locations of controls

points by measurement of distances, using the geometry of triangles. In

contrast to triangulation it does not involve the measurement of angles.

b

a

c

d

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In order to use the relative positioning, a proper number of control points are needed. These points: • are coordinated points; • are marked.

How to create a countrywide coordinate system?

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Control Networks

• Why is it necessary to have a common countrywide coordinate system?

• Many engineering tasks cover a large area (highways, bridges, tunnels, channels, land registry, etc.), where the common coordinate system (reference system) should be available.

• The Control Network provide us with control points given in the same refence system (coordinate system).

• Thus measuring the relative positions of unknown points using these control points, the coordinates of the new points can be computed in the same reference system.

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One of the Ground Control Points Established with Promark 3 for

Mapping Project

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Basic elements of a coordinate system

• an origin, then the

location of every

other point can be

stated in terms of

• a defined direction and

• a distance in the direction

Coordinate Systems-Basics 26

• Coordinate System can be

• 2D or 3D

• Types of coordinate systems

• (1) Geographic coordinates (f, l, z)

• (2) Global Cartesian coordinates (x, y, z): A system for the whole earth

• (3) Projected coordinates (x, y, z) on a local area of the earth’s surface

• The z-coordinate in (2) and (3) is defined geometrically, and in (1)

the z-coordinate is defined gravitationally.

Coordinate Systems - Basics 27

• The most widely used global coordinate system consists of lines of

geographic latitude (phi) and longitude (lambda).

• Lines of equal latitude are called parallels. They form circles on the surface

of the ellipsoid.

• Lines of equal longitude are called meridians and they form ellipses

(meridian ellipses) on the ellipsoid

• The equator is the largest circle and divides the earth in half.

• The prime meridian is the line of longitude that passes through Greenwich

England and defines the origin (zero degrees) for longitude coordinates.

Coordinate Systems-Basics 28

• The latitude (f) of a point P is the angle between the ellipsoidal normal through P and the equatorial plane.

• Latitude is zero on the equator (f = 0°), and increases towards the two poles to maximum values of f = +90 (90°N) at the North Pole and f = - 90° (90°S) at the South Pole.

• The longitude (λ) is the angle between prime meridian ellipse and the meridian ellipse containing the point P.

• It is measured in the equatorial plane from the meridian of Greenwich (λ = 0°) either eastwards through λ = + 180° (180°E) or westwards through λ = -180° (180°W).

Coordinate Systems-Basics 29

z

Coordinate Systems-Basics 30

Coordinate Systems-Basics

• 3D geographic coordinates (f, l, z) are obtained by introducing the ellipsoidal height z to the system.

• The ellipsoidal height (z) of a point is the vertical distance of the point in question above the ellipsoid.

• It is measured in distance units along the ellipsoidal normal from the point to the ellipsoid surface.

• 3D geographic coordinates can be used to define a position on the surface of the Earth (point P in figure).

3D Geographic coordinates (f, l, z) 32

z

• At equator

• Circumference of earth=40,075.16 kilometers

• Angle cover in circle=360o

• Therefore; 1 degree represents approximately 111 km

Angle Vs Distances on surface of earth

• An alternative method of defining a 3D position on the surface of the Earth is by means of geocentric coordinates (x ,y, z), also known as 3D Cartesian coordinates.

• The system has its origin at the mass-centre of the Earth with the X- and Y-axes in the plane of the equator.

• The X-axis passes through the meridian of Greenwich, and the Z-axis coincides with the Earth's axis of rotation.

3D Cartesian coordinates/ Geocentric coordinates

The three axes are mutually orthogonal and form a right-handed system.

Geocentric coordinates can be used to define a position on the surface of the

Earth (point P in figure).

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• A map projection is the systematic transformation of locations on the earth (latitude/longitude) to planar coordinates

• The basis for this transformation is the geographic coordinate system

(which references a datum)

• Map projections are designed for specific purposes

Projected Coordinate Systems

Curved Earth

Geographic coordinates: f, l (Latitude & Longitude)

Flat Map

Cartesian coordinates: x,y

(Easting & Northing)

Scale

• The proportion which the

distance between any two

points on map bears to

the horizontal distance

between the same two

points on the ground.

Methods of Expressing Scale • IN WORDS

Words explain the distance on map that represents a certain distance on ground.

e.g 1 Inch or 1 cm =1 Mile etc.

• BY REPRESENTATIVE FRACTION

The distance on map is represented by a fraction of corresponding distance on ground.

e.g 1:50,000 , 1/10,000 etc.

• BY SCALE LINE

By drawing a scale line showing the digits or parts for measuring distance on the map.

Errors in Measurements

• Errors in measurements • Sources of errors

• Natural causes

• Instrumental imperfections

• Personal limitations

• Types of errors

• Systematic or cumulative • Systematic errors can be calculated and proper corrections are applied

to the observation.

• Accidental, random or compensating

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Precision and Accuracy of Measurements

• True value of a quantity is never known

• Accuracy is the closeness or nearness of the measurements to the

“true value” of quantity being measured.

• Precision (or repeatability) refers to the closeness with which the

measurements agree with each other.

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