CIVL102 Surveying and Surveying Camp

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CIVL102  Surveying and Surveying Camp 
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Basic Goal of Surveying

• Obtain positions of built objects (3D)
• Graphical representation of the results
• Paper form as a contour map
• A plan at some suitable scale
• Digital format (CAD)

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Two Main Categories by size

• 1. Geodetic Surveying
• Large areas
• Considers curvature of the earth
• Purposes
• Determine figure of the earth (the geoid) and
  gravity field
• Provide an accurate framework for a large survey

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The Geoid

• Mean sea level (M.S.L.) surface extended over the
  whole earth
• Equipotential surface
• Perpendicular to direction of gravity
• Variations in the earths mass distribution
• Geoid has irregular shape
• Cannot be mathematically described in closed
  form.

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Best-fitting Ellipsoid Model

• Geodesists often use the ellipsoid that best
  fits the geoid
• Points on/ near earth surface
  
• Given by geodetic latitude, longitude and height
  above ellipsoid

Fig. 1.1 The geoid (irregularities
greatly exaggerated)
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• Popular ellipsoid model
• Geodetic Reference System of 1980 (GRS80)
• Equatorial semi-axis a 6378.1370 km
• Polar semi-axis b 6356.7523 km
• Distortion inevitable when plotting a curved
  surface onto a flat map
• Various map projection methods (mathematical
  geodesy)

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Second Main Category by size

• 2. Plane Surveying
• Relatively small areas
• Surface of the earth infinite horizontal plane
• Direction of gravity
• Constant over the entire site.
• Defines vertical lines ( plumb lines),
• Plane normal to a plumb line horizontal
  plane.
• Rectangular coordinate system most suitable
  for plane surveying

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• For distance measurements
• Flat earth assumption acceptable (up to 10 km ?10
  km)
• 10 km arc on earth surface longer than subtended
  chord by lt 10 mm
• percentage error in length measurements
• lt 10/10000000 1 ppm (parts-per-million)
  
• Laser instrument typically error 5 ppm
• Steel tape no better than 100 ppm.
• Plane surveying suffices for all but the largest
  surveys
• (for horizontal
  distances)
• Geodetic surveys seldom performed by engineers
  in private
• practice

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Types of Surveying

• Also classified by purpose - common types
• Topographic surveys
• Determine locations elevations of natural
  constructed objects on the ground
• For map making
• Concerns all features of the landscape that can
  be shown for the particular map scale

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• Cadastral surveys
• Determine lawful boundaries areas of properties
  rather than detail features of the landscape
• Used in legal disputes, taxation, etc.
• Also called property surveys / boundary surveys

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• Engineering surveys
• Surveying work for engineering projects before,
  during after construction
• E.g. setting out of tall buildings and dams
  deformation monitoring after completion
• Others
• Mining, hydrographic, highway, railroad, and
  tunnel surveys

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In our course

• Mainly topographic and engineering surveying
• Implicit assumption
• Small sites
• Theory and techniques of plane surveying will
  suffice
• Note
• Flat earth assumption may not hold for
  determination of elevations
• Tangent plane deviates from spherical earth by
• 2 m _at_ 5 km from point of tangency
• 8 m _at_ 10 km (see Ex. 1.2).
• Effects due to the earths curvature remedies
  Ch.2.

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• Survey results
• Often plotted on a plan
• True-to-scale representation of the area in a
  horizontal plane
• Measured slope (inclined) distance
• Plotted horizontal projection
• Height information conveyed on plan use
• Contour lines, or
• Spot levels (small s with heights printed
  alongside)

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• Consider Fig. 1.2
• Physical points A, B, and C
• Essential information for plotting
• Projections AB AC
• In horizontal plane containing A (or any other
  horizontal plane)

Fig. 1.2 Basic measurements in
surveying
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Fundamental techniques in surveying

• 5 basic quantities
• Slope distance AB, along with
• Vertical angle BAB (or zenith angle AAB),
• Horizontal distance AB AB cos(BAB)
• Vertical distance BB
• Similar measurements fix C relative to A,
• Horizontal angle BAC also needed to orient C
  relative to AB on the plot

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Other methods of measurement

• Plan distance (e.g. AB) by taping directly
• Height difference (e.g. BB, rise from A to B) by
  differential leveling (Ch. 2)
• Detailed techniques subsequent chapters.
• Essential characteristic about surveying
• Before final details (such as C) can be surveyed
  need reference points (e.g. A and B) to base the
  measurements on.

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Control survey

• Establish reference monuments
• Control points
• Accuracy greatly affects final results
• Often run as first stage of survey project

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Coordinate Systems

• Coordinates to be calculated before plotting
  survey results
• Use of appropriate coordinate system
• Plane surveying
• Righted-handed, rectangular coordinate system
• x-y axes on horizontal plane
• z-axis // direction of gravity
• Still need
• Suitable origin and orientation
• Based on physical entities

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For local construction purposes

• An artificial system may suffice, e.g.
• choose convenient point A on site as origin
• Usually assigned ve (large) x, y coordinates -gt
  all positive horizontal coordinates in the area
• Point B picked relative to A
• Line AB (horizontal projection) defines
  artificial north
• AB often chosen // (or per.) to most building
  lines
• Height 0 (or other reference value) assigned to
  a convenient point
• All other coordinates calculated relative to these

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Surveys over extended public areas

• Often tied to an official coordinate system
• Primary level of control from government
  authority
• Official rectangular coordinate system usually
• x- and y-axes directions of east and north
• Coordinates values along x, y axes eastings (E)
  and northings (N)
• Origin usually in the country / region assigned
  ve large (E, N)
• all other horizontal coordinates positive
• 0 of z-axis often defined at mean sea level
  (M.S.L.)

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Measuring angles and directions

• Compass
• Observe bearings
• Used in reconnaissance and hasty work
• Theodolite
• A telescopic sight pivoted both horizontally
  vertically
• Built-in graduated circles for measuring
  horizontal vertical angles
• Angles usually displayed in the ?// system
• 2? radians 360? (degrees) 1? 60 (minutes)
  1 60 (seconds)

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• Theodolites sold in Europe g/c/cc system angles
  in gons (or grads)
• 360? 400g (gons) 1g 100c 1c 100cc
• Note 50g79c98cc conveniently expressed as
  50.7998g
• Theodolites used on construction sites 20, 6,
  5 or 3 of arc
• Geodetic theodolites 1 or even 0.1

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Optical theodolite angle readings
Electronic theodolite with EDM mounted on top
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Measuring lengths
Fiberglass measuring tape

• Measuring tape
• Direct linear measurements
• Cheap
• For small details

Steel tape
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Electronic Distance Measurement (EDM)

• Laser equipment for very accurate distance
  measurement
• Measure up to thousands of meters with only a few
  mms error
• Used in all serious control work, and often in
  detail surveys as well

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EDM
EDM rechargeable battery
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Measuring height differences

• Level staff
• Level has telescope that can rotate about
  vertical axis, maintaining horizontal line of
  sight
• Staff long rod held vertically over point of
  interest, provides height readings to be read by
  the level
• A pair of readings determines the change in height

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Staff
Readings on a staff
Automatic Level
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The tripod

• Three-legged stand with pointed metal shoes
• Most surveying instruments mounted on top of
  tripods during use
• Tripod legs maneuvered to make instrument
  roughly horizontal centered over the station
  marker, followed by fine adjustments on the
  instrument.

Surveying equipment mounted on a wooden tripod
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More advanced instruments

• Total station
• Theodolite, EDM, data processor display unit
  combined
• Instant data conversion into 3-D coordinates
• Interface with computers

Total station with memory cards
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• Aerial camera
• Produces aerial photos for topographic,
  engineering, cadastral surveys
• Stereoscope
• Used to view stereoscopic pairs of aerial photos
  approximate heights of objects can be determined
  by stereoscopic viewing.
• Global Positioning System (GPS)
• Satellites-based systems giving accurate 3-D
  coordinates of point on earth occupied by a GPS
  receiver. Also used for navigation purposes

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Computing tools

• Computers, plotters, spreadsheets CAD
  invaluable tools for the surveyor
• Saves hours of time potential mistakes
• Applications
• Automating long routine calculations (Ch.2,4)
• Least squares adjustment (Ch.1,2,3,4)
• Graphical solutions (Ch.3,4,6)
• Plotting thousands of points with little effort
  (Ch.5),
• etc.

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Preliminaries, Planning, General Rules

• Any survey project
• Involves a series of measurements
• Errors accumulate
• Fundamental principle of surveying
• Work from the whole to the part

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1. Establish overall framework

• Covering the whole area
• Refined methods instruments
• Minimal number of points
• minimize error

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2. Fill in details based on accurate control
framework

• Cheaper quicker methods used
• meaningless for subsequent measurements to be
  more precise than underlying framework
• Carry out all measurements ( calculations) so
  that final product meets accuracy required by the
  purpose of survey
• Suit the means to the end since accuracy is
  costly in speed resources.