[Xastir] TOPOS with Xastir

[Tom Russo]

On Tue, Nov 13, 2007 at 12:29:25PM -0500, we recorded a bogon-computron collision of the <ewdavenport at certin.com> 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