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Monday, March 21, 2005

GeoPDF Hacks: Georegistering UTM Maps with Transverse Mercator

The Universal Transverse Mercator system is a widely-used grid system, and its enthusiasts have pushed its use beyond limits placed upon its specification. There are plenty of maps that represent areas that lie in one UTM zone by projecting them in some other zone. Often, this is an adjacent zone, but not always. The MAP2PDF plugin can be cantakerous if you try to use UTM as the map coordinate system for maps that do not lie cleanly in the appropriate zone. What to do? What I do is drop back and punt the UTM (menu selection, not system) for Transverse Mercator. Here's how to do it:

  1. Pick Transverse Mercator for your map coordinate system

  2. Take the UTM zone you want and multiply it by 6. E.g., Zone 16 gets you 96.

  3. Subtract 183 from the result. Zone 16: 96 - 183 = -87

  4. Enter that value for Central Meridian

  5. Enter 500000 for False Easting

  6. If the map is in the Northern Hemisphere, enter 0 for False Northing, else enter 10000000 (ten million)

  7. Enter 0.9996 for your scale factor

  8. Georegister as normal


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