CIVL102 Surveying and Surveying Camp

1. CIVL102 Surveying and Surveying Camp

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)

3. 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

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

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. 1.1 The geoid (irregularities greatly exaggerated)

6. 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)

7. 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

8. 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) Geodetic surveys: seldom performed by engineers in private practice

9. 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

10. 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

11. 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 tunnelsurveys

12. 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 earth’s curvature & remedies: Ch.2.

13. 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)

14. 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

15. Fundamental techniques in surveying 5 basic quantities: • Slope distance AB, along with • Vertical angle B’AB (or zenith angle A’AB), Horizontal distance AB’ = AB cos(BAB’) Vertical distance B’B • Similar measurements: fix C relative to A, • Horizontal angleB’AC’ also needed to orient C relative to AB’ on the plot

16. Other methods of measurement • Plan distance (e.g. AB’) by taping directly • Height difference (e.g. B’B, 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.

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

18. 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

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

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.)

21. 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)

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”

23. Optical theodolite & angle readings Electronic theodolite with EDM mounted on top

24. Measuring lengths Measuring tape • Direct linear measurements • Cheap • For small details Fiberglass measuring tape Steel tape

25. Electronic Distance Measurement (EDM) • Laser equipment for very accurate distance measurement • Measure up to thousands of meters with only a few mm’s error • Used in all serious control work, and often in detail surveys as well

26. EDM EDM & rechargeable battery

27. 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

28. Staff Readings on a staff Automatic Level

29. 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

30. 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

31. 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

32. 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.

33. Preliminaries, Planning, & General Rules Any survey project: • Involves a series of measurements • Errorsaccumulate Fundamental principle of surveying: Work from the whole to the part

34. 1. Establish overall framework • Covering the whole area • Refined methods & instruments • Minimal number of points minimize error

35. 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.