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Published byEthan Cushen Modified over 2 years ago

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

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

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Presentation Title 3 Our Fix

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Presentation Title 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 = m 1 degree long = m At 50N: 1 degree lat = m 1 degree long = m

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Presentation Title 5 Source ASRP UKH601 Sample source ASRP UKH601

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

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

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Presentation Title 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

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Presentation Title 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 = rads Meters per degree Longitude: = * cos(2* rlat) *cos(4*rlat) = * cos(2* )+1.175*cos(4* ) = = m/degree latitude Meters per degree Latitude: = * cos(rlat) * cos(3*rlat) = * cos( ) * cos(3* ) = = m/degree longitude

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

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Presentation Title 11 Resampler Workspace

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

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Presentation Title 13 Theory & References Converting UTM to Latitude and Longitude (Or Vice Versa); Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay An on-line calculator implemented with Java Script can be seen on the Federation of American Scientists website at: An example function implementation from Physical Oceanography, U of California, San Diego

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Presentation Title 14 Global Projections Mercator Demo: Canada as the centre of the Universe

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Presentation Title 15 Mercator - default

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Presentation Title 16 Mercator - Clipped

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