# MrSid GeoViewer (DOQQ viewer) X/Y Coords and Lat Lon

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Does any one know the relationship between the x y coordinates displayed by the Lizard Tech MrSid GeoViewer program and Latitude and Longitude?For example, when over the airport DOQQ (Digital Ortho Quarter Quad) aerial photo that I am interested in, MrSID (the program) displays x = 251294 y=262955 in meters.I know that the coordinates of the airport are about 46 31.5 N and 114 03.1 W. Further, from a different program, I know that the Universal Transverse Mercator (UTM) coordinates for this airport in Zone 11 are approximately Lat = 726122 meters, Long 5156605 meters.So if you know 251294 relates to approx. 46 31.5 or 726122, I would appreciate your response. Thank you.Larry Jones

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It depends on what coordinate system (datum and projection) your coordinates are representing. I haven't used MrSid before but there should be an option to find the coordinate system being used. The aerial photo should be georeferenced to a coordinate system already and those are the coordinates you need to use. From the x and y's you've got there, it sounds like it could be a UTM projection but based on a local origin. If your aerial photo is using the WGS84 coordinate system (or one based on the GRS80 ellipsoid) then it is a simple matter of changing Mr Sid to show WGS84 latitude and longitude instead of x and y.Hope this helps,Derek

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Thanks for your response Derek. I'm still confused. I don't know what the local origin of the DOQQ is, and how to relate that to the MrSID coordinates. The header of the DOQQ does specify an XY Origin shown below but that doesn't look like a UTM coordinate. The Y coordinate is not large enough, is it? XY_ORIGIN[2]: 245546.5 288737.5 MrSid GeoViewer (available at http://www.lizardtech.com/download/?f=0&d=1) doesn't output Lat and Long. as far as I can tell. It just outputs X and Y pixel coordinates in meters. What their reference is, is a mystery. However, the MrSID compressed DOQQ is definitely WGS84 referenced. I can determine by definition the corner coordinates (A DOQQ is a quarter quadrangle there are four Quarter Quads that cover each 7.5 x 7.5 minute quadrangle) of the DOQQ but how does that corner (Lat and Long) relate to the "Meters" offered up by MrSID? Here's where you can get a sample of a DOQQ that MrSID can "view". http://nris.state.mt.us/nsdi/doq.html The possible joy in all this is that MrSID allows one to export a selected portion of the DOQQ Aerial Photo(say an aiport or city) to a .tiff which can be converted to a bitmap and (I think) used as a custom texture. If I only knew the NW corner coordinates of the output!Thanks again.Larry Jones

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<>Larry, I don't understand, using all or any part of a DOQQ is already simple, no need for a utility to help...if I understand you correctly. Just download the desired doqq(s) from terraserver, and save. Open in any graphics program and crop, convert to bmp from jpg, colorize...have fun. save as desired format and voila...you have your texture master.Bob Bernstein

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Thanks Bob. I've tried to use Terraserver in the past but assembling the many photos to cover the area I want, I found to be difficult if not impossible. I've found you're better off assembling the photos you want from files directly downloaded. In the case of Montana, the state has stitched many of the quarter quads together already. Turns out here is THE answer to my original question: (Should anyone walk down this path again...)The MrSID coordinates I was trying to decipher are coordinates in the Montana State Plane. To convert these coordinates into LAT / LONG, you can use a perl program found at http://www.ngs.noaa.gov/cgi-bin/spc_getpc.prland other locations.Note that while the UTM zone was 11, the state plane zone is 2500.Larry

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