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  • Slide 1
  • CIVL102 Surveying and Surveying Camp CIVL102 Surveying and Surveying Camp
  • Slide 2
  • 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: Variations in the earths mass distribution: Geoid has irregular shape Cannot be mathematically described in closed form.
  • Slide 5
  • 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. 1.1The 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 < 10 mm percentage error in length measurements: < 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) (for horizontal distances) Geodetic surveys: seldom performed by engineers in private practice 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 @ 5 km from point of tangency ~ 8 m @ 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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  • 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 Fundamental techniques in surveying
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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 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
  • Slide 19
  • 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 -> 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
  • Slide 20
  • 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)
  • Slide 22
  • 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 Measuring tape Direct linear measurements Cheap For small details Fiberglass measuring tape Steel tape
  • Slide 25
  • 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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  • Automatic Level Staff Readings on a staff
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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