12/26/2012. Geographic Information Systems * * * * GIS (... yrezaei

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1 ( - Geographic Information Systems ( ( 1

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4 Information System Data base DB IS IS DB (Knowledge ( ( (System (Information System - (Georefrence Analysis Data + Knowledge ======== Information 4

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13 Geographic Coordinate System The geographic coordinate system is the location reference system for spatial features on the Earth s surface (Spatial (Attribute Data - The geographic coordinate system is defined by longitude and latitude - - ( ( 26 ( 13

14 THE GEOID and ELLIPSOID h = H + N P Earth's Surface Earth Surface Ellipsoid, Geoid, Topo Ellipsoid h Q N reference ellipsoid P o "Geoid" reference geoid OCEAN h (Ellipsoid Height = Distance along ellipsoid normal (Q to P N (Geoid Height = Distance along ellipsoid normal (Q to P o H (orthometric height = Distance along Plumb Line (P o to P SOURCE National Geodetic Survey http//wwwngsnoaagov/geoid/geoid_defhtml real surface also called the topographic surface 14

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16 Approximation of the Earth 32 The simplest model is a sphere, which is typically used in discussing map projections But the Earth is not a perfect sphere the Earth is wider along the equator than between the poles Therefore a better approximation to the shape of the Earth is a spheroid, also called ellipsoid, an ellipse rotated about its minor axis 31 16

17 WGS84, MSL, h Datum A datum is a mathematical model of the Earth, which serves as the reference or base for calculating the geographic coordinates of a location A shift of the datum will result in in the shift of positions of points 33 17

18 Geographic Latitude/Longitude in system Geographic Latitude/Longitude on a flat surface (WGS 84 datum 90? West East -180? equator 0? Prime Meridian 0? North 180? South Scale, distance, area, and shape are all distorted with the distortion increasing toward the poles -90? open Arc for a demo 18

19 Cylindrical Transverse Cylindrical Oblique Cylindrical Secant Cylindrical Case and projection Conical Secant Conical Planar Secant Planar 37 19

20 Source Longley et al

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23 UTM Zone Numbers The central meridian in this secant case transverse Mercator projection has a scale factor of The two standard lines on either side of the central meridian have a scale factor of

24 ( ( UTM Coordinates In the N Hemisphere define the Equator as 0 mn The central meridian of the zone is given a false Easting of 500,000 me Eastings and northings are both in meters allowing easy estimation of distance on the projection A UTM georeference consists of a zone number, a six-digit easting and a seven-digit northing Eg, 14, E, N 24

25 Field Data Collection Using a Total Station Field surveying & GPS Photogrammetry Remote sensing Existing maps & documents GPS 25

26 Surveying Techniques 3 Levels of GPS Surveying Point Positioning DGPS (Differential Precision Surveying (Phase Precision Surveying (Phase Observable 26

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28 (Orthophoto 3D (DSM 3D Laser Scanning 28

29 RS Data Updating RS & Integration (n> ( Analysis Results Photogrammetry & Integration Photogrammetry Data Input Control Computations Plotting 29

30 Automatic Semi Automatic Manually R2V On Screen Digitizing ( ( ( ( Scanning Digitizing On Screen Digitizing = Head Up Digitizing 30

31 Selecting a Digitizing Technique 31

32 (Spatial Data Model 32

33 Spatial Data (Data Model Vector Data Land Ownership Raster Data (Vector Point, Line, Polygone (Raster Pixel, value Transportation Surface Waters Elevation Aerial Imagery Boundaries Geodetic Control 33

34 A B A B A or B? (Space Filling ( DEM ( Spans, Ilwis O 1 O O 2 O O O O 1 0 WATER 1 HIGHLAND 2 WETLAND O 0O O O O O O 1 34