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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
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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.
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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
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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
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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
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
17
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
18
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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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
22
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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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
• 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
38