[GRASS-user] new user setting up a new mapset/project

[Tom Russo]

On Sun, Jul 20, 2008 at 08:28:54PM -0700, we recorded a bogon-computron collision of the <mtnbiketrail at zzz.com> flavor, containing:
> I'm confused.
> I want to set up a new project and use UTM wgs 84.
> But, some of my data is drg(base USGS topo map), which are lat/long,  

Most USGS DRG topo maps are georeferenced in UTM (only those that have been
monkeyed with by other agencies are not).  Some state and local GIS departments
reprocess them with software that removes the TIFF tags that GDAL would use
to figure out what to do with them, even when they don't change the projection.
Any USGS topo for California will have been reprojected to an equal-area 
projection, and any USGS topo covering territory under the authority of the 
Tennesee Valley Authority will be in UTM but with no geotiff tags necessary
for GDAL to recognize them.  But real USGS topos for any other part of the
US should be in UTM and have GeoTIFF tags identifying the coordinate system.

What does the following command output?
   gdalinfo file.tif

That'll tell you for sure.  If you see the line
  Coordinate System is `'
then you have a file that has all the geotiff tags missing.  If it says 
anything else, then the file contains information that tells you what
coordinate system it uses.

If the tags are missing, but you have .tfw files and other metadata that tell 
you for sure what the coordinate system of the file really is, then you can 
often re-insert the appropriate tags with a gdal_translate command.

I second Mortiz' comment about the misuse of "-o" to r.in.gdal.  It is better
to understand exactly what the coordinate system of your image file is and
get it imported in a location where -o is not necessary than to just force
r.in.gdal to ignore projection problems.

> and the field data I want to use is x,y( I have UTM coords which I can  
> georeference to).
> So when I set up the project, which coord should I use?
> 
> When I went to use UTM, I did not understand how to get the north,  
> south, east, west info. Grass did not like the tiff, and associated  
> tfw for the base map.

If the file is a real USGS DRG file from USGS (and not reprocessed by someone
else) then it should be possible to create a new location from the .tif file
by doing
  r.in.gdal input=file.tif location=newlocation output=somename
The new location will have the right coordinate system IF the tif file had 
the correct GeoTIFF tags that USGS puts in.  If the files were reprocessed
by some other agency, all bets could be off and you'd have to do more work
to get it done right.

-- 
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
 "Argue for your limitations and sure enough, they're yours."  -- R. Bach