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Lecture 4

Lecture 4. Understanding Coordinate Systems. Geographic Coordinate systems. Spherical Ellipsoidal Curved. GCS. Projected coordinate systems. (PCS) 2D Flat Planar Cartesian. GCS. PCS. GCS has angular units of measure. Degrees 360 per circle Decimal degrees Degree, minute, second

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Lecture 4

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  1. Lecture 4 Understanding Coordinate Systems

  2. Geographic Coordinate systems • Spherical • Ellipsoidal • Curved GCS

  3. Projected coordinate systems • (PCS) • 2D • Flat • Planar • Cartesian GCS PCS

  4. GCS has angular units of measure • Degrees • 360 per circle • Decimal degrees • Degree, minute, second • Radians • 2 pi per circle • ~6.3 per circle (~57 degrees each) • Gradian • 400 per circle • Gon • Same as gradians • To some grad = degree

  5. PCS has linear units of measure • Linear units • Meters • Feet • X and Y coordinates • Length, angles, and areas are constant Y Data usually here X + Y + X - Y + X X - Y - X + Y -

  6. Map projection • Math to transform GCS

  7. Map projection • Math to transform GCS to PCS • Flattening the earth – round to flat • Distortions make geographers SADD • Shape, Area, Distance, and Direction Plate Carrée projection

  8. PCS properties example • Name – NAD 1983 UTM Zone 11N • GCS– NAD 1983 • Map Projection – Mercator • Projection parameters • Central meridian, latitude of origin, scale factor, false easting • Linear unit of measure (i.e., meters)

  9. Geographic coordinate systems • Mathematical model of a planetary body - spheroid • Parameters describe the spheroid shape • Smooth, without imperfections • GCS for earth, planets, and more Earth Mars IO

  10. GCS properties • Spheroid • Major and minor axis • Units (lat/long, radians, grads)

  11. GCS properties • Spheroid • Major and minor axis • Units (lat/long, radians, grads) • Datum • Spheroid’s position in relation to actual earth • Local datum: spheroid touches edge of earth, good fit there Great fit here Bad fit here Local datum

  12. GCS properties • Spheroid • Major and minor axis • Units (lat/long, radians, grads) • Datum • Spheroid’s position in relation to actual earth • Local datum: spheroid touches edge of earth, good fit there • Earth-centered: spheroid and earth center match All around best fit for the entire planet Great fit here Bad fit here Local datum Earth-centered datum

  13. GCS properties example • Name • European Datum 1950 • Datum • European Datum 1950 • Spheroid • International 1924 • Prime Meridian • Greenwich • Angular unit of measure • Degrees

  14. GCS with a local datum • Spheroid

  15. GCS with a local datum • Datum • Spheroid’s position in relation to actual earth

  16. GCS with a local datum • Datum • Spheroid’s position in relation to actual earth

  17. GCS with a local datum • Datum • Spheroid’s position in relation to actual earth

  18. GCS with a local datum • Datum • Spheroid’s position in relation to actual earth

  19. GCS with a local datum • Datum • Spheroid’s position in relation to actual earth

  20. GCS with a local datum • Datum • Spheroid’s position in relation to actual earth • Local datum: spheroid touches edge of earth, good fit there • Bad fit on the other side

  21. GCS with an Earth Centered datum • Spheroid

  22. GCS with an Earth Centered datum • Datum • Spheroid’s center matched to earth center

  23. GCS with an Earth Centered datum • Datum • Spheroid’s center matched to earth center

  24. GCS with an Earth Centered datum • Datum • Spheroid’s center matched to earth center

  25. GCS with an Earth Centered datum • Datum • Spheroid’s center matched to earth center

  26. GCS with an Earth Centered datum • Datum • Spheroid’s center matched to earth center

  27. GCS with an Earth Centered datum • Datum • Spheroid’s center matched to earth center • Best fit all around the earth

  28. Common GCS parameters in use today (US) • As measurement gets better, new GCS are defined • NAD27 – parameters defined in 1866 (log tables) • NAD83 – parameters defined in 1979 (pre-GPS) • WGS84 – parameters defined in 1984 (GPS) North American Datum 1927 North American Datum 1983 World Geodetic Survey 1984

  29. Warning: different geographic coordinate system…

  30. Geographic transformation • Math to transform from one GCS to another ESRI-Redlands 117 Degrees 11 Minutes 39.2 Seconds West 34 Degrees 3 Minutes 23.1 Seconds North NAD 27

  31. Geographic transformation • Math to transform from one GCS to another • Changing GCS changes the lat/long for same point • The same spot on earth has differing coordinates ESRI-Redlands 117 Degrees 11 Minutes 42.36 Seconds West ESRI-Redlands 117 Degrees 11 Minutes 39.2 Seconds West 34 Degrees 3 Minutes 23.14 Seconds North 34 Degrees 3 Minutes 23.1 Seconds North NAD 83 NAD 27

  32. ArcMap’s GCS and PCS behavior • Data frame - has both • Spatial data - has GCS, may have PCS • Metadata - prj, XML, mdb, or none • Tools that help

  33. On-the-fly projection • ArcMap data frames have a GCS and a PCS • You should set them • If not set, data frames take first layer’s GCS/PCS Data frame: Bonne PCS

  34. On-the-fly projection • ArcMap data frames have a GCS and a PCS • You should set them • If not set, data frames take first layer’s GCS/PCS • If needed, new layers are projected on-the-fly (to match) • If no CS metadata, new layer cannot be projected on-the-fly Input layer: Robinson PCS Data frame: Bonne PCS ArcMap projects data on-the-fly into a data frame

  35. GCS and PCS metadata for spatial data • Stored in internal geodatabase tables • Stored in projection files • Shapefiles can have a .prj text file (e.g., streets.prj) • Coverages can have a prj.adf text file (e.g., /rivers/prj.adf) • Stored optionally in XML files created by ArcCatalog • Non-native ESRI datasets use various other formats

  36. Warning! • GCS and PCS metadata is NOT required • You might get data that is missing its coordinate system metadata • If researched and discovered, you can add it • If not, use Spatial Adjustment to move the data into place

  37. Problem Solution Spatial reference problems and solutions  You know the coordinate system information, but it is missing  Define Projection tool • Project tool or data frame project on-the-fly • The PCS is defined correctly, but is not the one you need  The GCS is defined, but it is not NAD27 or NAD83 • Project tool or set a geographic transformation in the data frame properties

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