Geo Referencing & Map projections CGI-GIRS 0910

Transcription

1 Geo Referencing & Map projections CGI-GIRS 0910

2 Where are you? 31UFT ,7 441, ' NB 5 40' OL 2/60

3 Who are they? 3/60

4 Do geo data describe Earth s phenomena perfectly? Georeference systems ellipsoid / geoid datum / reference surfaces sea level Map projections properties projection types UTM coordinate systems Geo-data cycle 4/60

5 Geo-reference systems Geo - Reference - Systems earth something to refer to coordinates physical reality < relation > geometrical abstractions 5/60

6 Garden maintenance objects need a reference Y X 6/60

7 Map projection 16 th century Waldseemuller 7/60

8 From round earth to flat earth Distance Angle Area Shape 8/60

9 What Projection? 9/60

10 Map projections Mathematical projections (abstract) from an ellipsoid to a map plane Numerous projections Projection plane always flat Cartesian coordinates Every country uses own projections Always purposely designed 10/60

11 Type of map projections Grouping by preserved properties: conformal: preserves local shapes global equivalent: represents areas in correct relative size global equidistant: maintains consistency of scale for certain distances - local azimuthal: retains certain accurate directions local but never for all together 11/60

12 Properties Tissot indicatrices: to show the distortion of parts of a map 12/60

13 Type of projection (projection surface) Projection plane Azimuthal Cylindrical Conical 13/60

14 Type of projection: aspect normal: transversal: oblique: Axis of Globe and Axis of Plane: identical Axis of Globe and Axis of Plane: perpendicular angles between normal and transversal Standard line simple case : 1 line of tangency (1 : 1 scale) secant case : 2 lines of tangency 14/60

15 Why many types of projections? 15/60

16 Cylindrical projections Conformal Equidistant Equal area 16/60

17 Cylindrical projections Equal area conformal at Equator conformal at higher latitudes (N & S) 17/60

18 Conical projections... defined for USA Conformal (Lambert) Equal area (Albers) 18/60

19 What projection? Criteria - Extent of Area, Precision - Area, Conformal, Distance - Standard line, line of tangency 19/60

20 Mercator projection - great circle 20/60

21 UTM M: Mercator projection T: transverse (cylinder axis perpendicular to globe axis) U: universal (60 projection zones of 6 degree latitude) 1Central line per zone 2 standard lines per zone (180 km to the west and the east of central line) False Easting and False Northing 21/60

22 UTM zones 22/60

23 UTM... a source of much confusion as UTM stands for different things: 1. UTM projection can be defined with different datums (ellipsoids) 2. UTM grid can be defined on other projections than UTM With UTM coordinates always check ellipsoid and projection 23/60

24 Dutch topographic map (1996) Map Scale Civil Bessel ellipsoid RD map grid Military WGS 84 ellipsoid (formerly Hayford) UTM map grid 24/60

25 UTM background UTM Grid Zones of the World Using UTM Coordinate system 25/60

26 Coordinates Coordinates in a map projection plane: Geographic coordinates angle East/West from 0-meridian (longitude) angle North/South from Equator (latitude) Cartesian coordinates distance from Y-axis (X-coordinate) distance from X-axis (Y-coordinate) 26/60

27 Geographic coordinate systems Location on the earth in Longitude and Latitude (e.g ' N 5 40' E ) Longitude based on parallels gives East-West Latitude based on meridians gives North South Its not based on a Cartesian plane but on location on the earth surface (spherical coordinate system) from the earth s centre 27/60

28 Latitude Longitude 28/60

29 Geodetic Highlights 29/60

30 Geographic coordinates Angular measures Degrees-minutes-second Lat 51 o ( degrees, minutes, seconds) Lon 5 o Decimal Degrees (DD) Lat (= degrees + minutes/60+ seconds/3600) Lon Radian 1 radian= 57,2958 o 1 degree = 0,01745 rad 30/60

31 Geometry as displayed on maps Map sheet or screen (material) shows: LL-graticule (degrees) meridians (E or W) parallels (N or S) suits positioning only XY-grid (kilometres) square raster suits geometric calculations as well 31/60

32 Dutch example 32/60

33 Dutch Reference 33/60

34 Dutch map grid Datum point: Amersfoort Datum: Bessel 1841 ellipsoid Projection: secant azimuth. False origin: X = m Y = m 34/60

35 Meta data of Dutch Topographic data maps PROJCS["Rijksdriehoekstelsel_New", GEOGCS["GCS_Amersfoort", DATUM["D_Amersfoort", SPHEROID["Bessel_1841", , ]], PRIMEM["Greenwich",0.0], UNIT["Degree", ]], PROJECTION["Double_Stereographic"], PARAMETER["False_Easting", ], PARAMETER["False_Northing", ], PARAMETER["Central_Meridian", ], PARAMETER["Scale_Factor", ], PARAMETER["Latitude_Of_Origin", ], UNIT["Meter",1.0]] 35/60

36 Geo-reference systems Geo - Reference - Systems earth something to refer to coordinates physical reality < relation > geometrical abstractions 36/60

37 Georeferencing in a nutshell Georeferencing is: Geometrically describing 3D-locations on the earth surface by means of earth-fixed coordinates 37/60

38 History Local National Continental (for at least 21 centuries) (since mid 19 th century (NL)) (since mid 20 th century) Global (since 1970 / GPS, 1989) 38/60

39 Good old days 39/60

40 Combination of reference systems 40/60

41 Good new days 41/60

42 Georeferencing is about (1) Measurements in the real world (material) to acquire: Positions via angles (triangulation) lengths (distances) time (GPS) Elevations via vertical distances (between gravity level surfaces) 42/60

43 Georeferencing is about (2) Abstract reference surfaces for: Horizontal: smooth ellipsoid for positions Vertical: irregular geoid for elevations 43/60

44 Datum and Spheroid Geodetic datum is the basis for geographical coordinates of a location which defines the size and shape of the earth and the origin and orientation of the coordinate systems used to map the earth. Spheroid (ellipsoid) approximates the shape of the earth Datum Example: WGS 1984 (world application) 44/60

45 Many Models of the earth Variables: a ~ 6378 km; b ~6356 km 45/60

46 Many different ellipsoids (a small selection) Datum: mathematical model of the Earth to serve as reference Ellipsoid Major axis. Unit of Flattening name a measure 1/f Clarke m Bessel m Everest 1830 (India) m GRS80 (New Intern l) m WGS m Various ellipsoids; selection adopted from M. Hooijberg, Practical Geodesy, 1997, p /60

47 Meridians of Europe Santa Maria degli Angeli e dei Martiri Clementus XI /60

48 Question Is it possible to have different coordinates for the same location? 48/60

49 Examples (Bellingham, Washington) NAD 1927 Lat Lon NAD 1983 Lat Lon WGS 1984 Lat Lon /60

50 Horizontal and vertical models One location: Horizontal datum: (ellipsoid) for position mathematical model egg Vertical datum: (geoid) for elevation physical model potato 50/60

51 Map Jumping 51/60

52 Difference in Mean Sea Levels 2 Netherlands Belgium Average height tide Den Helder (North Sea) Average low tide Oostende (Dover Channel) A visible elevation jump of From m, via into m from Netherlands to Belgium???? 52/60

53 Difference in Mean Sea Levels Differences between Height Reference Levels within Europe see Augath, Ihde, 2002 page GRS /60

54 Two different abstract models One location, but yet: Two different positions Two different heights : orthometric (related to geoid) = H geodetic (related to ellipsoid) = h = H+N geoid undulation = N ( potato minus egg ) 54/60

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56 Rotating potato Mean gravity level at mean sea level 56/60

57 Geoid undulation (global) m 0 m 80 m 57/60

58 Towards a very accurate geoid (GRACE) NASA ESA twin satellites ( Tom & Jerry ) launched March 2002 detailed measurements of Earth's gravity field Orbiting Twins - The GRACE satellites GRACE animation with oral explanation 58/60

59 Summary Georeferencing Geometry Plane projection (flat earth model) vs. Spherical projection (round earth model) Coordinate systems Geographic coordinates (latitude and longitude) Geocentric coordinates (X, Y, Z mass centre of the earth) Cartesian coordinates Grids Datums Horizontal and Vertical references Ellipsoid / Geoid / Mean Sea Level Vertical elevation / Geoid undulation Role of Gravity Map projections Properties: shape, area, distance, angle UTM, RD, false origin 59/60

60 Something to refer to Geographic coordinates RD coordinates Horizontal reference!! Principal scale Local scale Map scale Earth Spheroid Projected Map Gridded Map Mathematical Representation Geo Datum Map Projection Plane Orientation Distortion Reference Transformation Grid False Origin 60/60

61 Study materials: Theory Chang, 2006, Chapter 2: Coordinate systems (except: 2.4.2;2.4.3; ) Practical: Exercise Module 3: Map projections Wageningen UR

62 Equidistant... a confusing concept, because: means equal in distance distance on earth surface equal to distance in map projection plane (scale 1:1) but only applied to specific directions all directions to a single point, or all perpendiculars to a single line An equidistant projection has NO uniform scale 62/60

63 Why horizontal and vertical differentiation? Example: distance D = 100 km: Horizontal deviation exponential increase of dd/d dd=1*10-6 * D 3 1 mm / 1 km 1 m Vertical deviation dh (mm) = 7,8mm/km * D 2 dh (mm) = 78 * D m 63/60

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