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Sep. 21-22, 2006

v. FME Worldwide User Conference – Vancouver. Sep. 21-22, 2006. Reprojection Problems: Art or Error? Dean Hintz, Safe Software. ASRP Mixes Cartesian and Polar LL84. All ASRP LL84 coords, But zone 1,8 are polar projections. Our Fix.

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Sep. 21-22, 2006

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  1. v FME Worldwide User Conference – Vancouver Sep. 21-22, 2006 Reprojection Problems: Art or Error? Dean Hintz, Safe Software

  2. ASRP Mixes Cartesian and Polar LL84 All ASRP LL84 coords, But zone 1,8 are polar projections

  3. Our Fix

  4. Need for Degrees to Meters conversion Based on Latitude The Problem: • 1 degree can represent radically different distances on the earths surface depending on where you are. • This can become a problem when defining a spatial reference. Image source resolution usually based on ground distance. • SDE rastermap: first tile in sets the resolution. For example, at the equator: • 1 degree lat = 110574m • 1 degree long = 111319m At 50N: • 1 degree lat = 111229 m • 1 degree long = 71696 m

  5. Source ASRP UKH601 Sample source ASRP UKH601

  6. SDE mosaic: Northern tile is loaded first UKH601 in SDE mosaic when EUH805 is loaded first

  7. SDE Mosaic: Southern tile is loaded first UKH601 in SDE mosaic when UKH601 is loaded first

  8. Approaches Considered Solution 1: force most southern tile to load first, or always use equitorial resolution. Solution 2: Calculate resolution based on minimum latitude

  9. Step 1: Calculate meters per degree for minimum latitude rlat = reference latitude in radians = reference latitude * pi/180 At 50 degrees N: • rlat = 50* pi/180 = 0.872665 rads Meters per degree Longitude: • = 111132.92 - 559.82 * cos(2* rlat) + 1.175*cos(4*rlat) • = 111132.92 - 559.82 * cos(2* 0.872665)+1.175*cos(4*0.872665) • = 111132.92 + 97.21 - 1.10 = 111229.0 m/degree latitude Meters per degree Latitude: • = 111412.84 * cos(rlat) - 93.5 * cos(3*rlat) • = 111412.84 * cos(0.872665) - 93.5 * cos(3*0.872665) • = 71614.79 + 80.97 = 71695.8 m/degree longitude

  10. Step 2: Calculate degrees per meter for desired resolution Meters = Degrees * (meters per degree) Degrees = Meters / (meters per degree) DegreesX = 100m / 71696 m per degree • =0.00139 degrees / 100 m per degree DegreesY = 100m/111229 m per degree • =0.000899 degrees / 100 m per degree Desired resolution at 50N for 100x100m pixel is: • X = 0.00139, Y = 0.000899

  11. Resampler Workspace

  12. SDE mosaic: tiles resampled to southern most resolution UKH601 in SDE mosaic when all tiles are resampled to UKH601 resolution.

  13. Theory & References Converting UTM to Latitude and Longitude (Or Vice Versa); Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay http://www.uwgb.edu/dutchs/UsefulData/UTMFormulas.htm An on-line calculator implemented with Java Script can be seen on the Federation of American Scientists website at: http://www.fas.org/news/reference/calc/degree.html An example function implementation from Physical Oceanography, U of California, San Diego http://www-pord.ucsd.edu/~matlab/coord.htm .

  14. Global Projections Mercator Demo: • Canada as the centre of the Universe

  15. Mercator - default

  16. Mercator - Clipped

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