CIVL102 Surveying and Surveying Camp CIVL102 Surveying and Surveying Camp

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)

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

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: Variations in the earth’s mass distribution: Geoid has irregular shape Cannot be mathematically described in closed form.

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)

Popular ellipsoid model: Geodetic Reference System of 1980 (GRS80) Equatorial semi-axis a = km; Polar semi-axis b = km Distortion inevitable when plotting a curved surface onto a flat map Various map projection methods (mathematical geodesy)

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

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/ = 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

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

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

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

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 5 km from point of tangency ~ 8 10 km (see Ex. 1.2). Effects due to the earth’s curvature & remedies: Ch.2.

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)

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

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 angle B’AC’ also needed to orient C relative to AB’ on the plot Fundamental techniques in surveying

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.

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

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

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

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.)

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)

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 g Theodolites used on construction sites: 20”, 6”, 5” or 3” of arc Geodetic theodolites: 1” or even 0.1”

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

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

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

EDM EDM & rechargeable battery

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

Automatic Level Staff Readings on a staff

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

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

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

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.

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

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

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. 2. Fill in details based on accurate control framework