On Tue, Nov 13, 2007 at 12:29:25PM -0500, we recorded a bogon-computron collision of the <[EMAIL PROTECTED]> flavor, containing: > Hi all > > I am trying to figure out how to use 1:25k Topos with Xastir so we can use > it with our Search and Rescue teams. > > I have reviewed as many Readme.maps and Wiki's that I have been able to > find.
> They have lead me to believe that I will have to create these charts from > other sources. > I have found that I can buy North Carolina County DRG files that I will > have to patch together for our ARES region If the DRG files are true USGS DRGs in GeoTIFF format, with UTM coordinates *AND* proper GeoTIFF tags that contain the coordinate system information, then they can be used in xastir directly out of the box. You should not need to patch them yourself if you can construct (or obtain) an "FGD" metadata file that has the bounding box of the map data in lat/lon. Xastir will use that fgd metadata file to clip off the collar of the maps and seamlessly tile them on demand. However, many state and county GIS departments reprocess the USGS DRG files into State Plane Coordinate System, and often do it with software that does not produce GeoTIFFs with the proper tags. If you have gdal installed you can examine the .tif files with gdalinfo. If it tells you what coordinate system is in use in the file, and that is UTM in the NAD27 or NAD83 or WGS84 datum, then you're good to go. If it's a state plane coordinate system, you have to gdalwarp the files first. If gdalinfo reports " `' " as the coordinate system, your DRGs have been reprocessed with ESRI Arc/Info and have no coordinate system tags. Your only hope to use them at that point is to obtain a clear statement from the organization providing the DRGs as to what coordinate system they're in, and use gdal_translate to tag them. Complete instructions for doing this (and everything I've said in this paragraph) are in the README.MAPS file in the Xastir distribution, under the heading "Defective GeoTIFF files need even more special processing." > Has someone already gone through this who is willing to point me in the > right direction? Many times, and that's why I wrote the "Defective GeoTIFF files need even more special processing" section of README.MAPS. -- Tom Russo KM5VY SAR502 DM64ux http://www.swcp.com/~russo/ Tijeras, NM QRPL#1592 K2#398 SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM "And, isn't sanity really just a one-trick pony anyway? I mean all you get is one trick, rational thinking, but when you're good and crazy, oooh, oooh, oooh, the sky is the limit!" --- The Tick _______________________________________________ Xastir mailing list [email protected] http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
