[GRASSLIST:2695] Re: stitching geotiffs

[Martin du Saire]

At 04:01 PM 2/19/2004 -0700, you wrote:
>Martin du Saire wrote:
>
>>Hi,
>>I am a newbie to GRASS (XT, Cygwin/XFree86; GRASS5.0) and GIS trying to 
>>stitch together a set of NLCD Geo-Tiff  (USGS Landsat-5, etc.) data files 
>>for a set of contiguous states in the US.  I finally figured out how to 
>>import them using r.in.gdal -o.  (If there is some inherent problem with 
>>overriding the projection checking, please let me know.)
>
>If you are importing an image in UTM Zone X into a location defined as UTM 
>Zone X, then you are doing the correct thing by using -o. (You should not 
>use -o to import Zone X into a location of Zone Y). You may also want to 
>use -e, which extends the location if needed.

So I can import a Zone X map into a Zone Y location?  Is this any 
better/worse than using r.proj?  The bulk of my area of interest is in a 
single UTM zone (Zone Y), so maybe the distortions generated by importing 
Zone X and Zone Z maps into a location of Zone Y will be small??


>>For starters, how do I go about importing the individual files with their 
>>corresponding UTM zone designations into the same project?
>
>Do I understand correctly that you have images in Zone X, Y Z ... and want 
>to have them all in a single projection? If I understand correctly, then 
>you need to use r.proj to reproject from the individual zones into the 
>single target projection. But maybe I do not understand you goal.

Yes, that is what I am attempting to do. I am stitching together maps for 
MN, IA (Zone 15), WI (Zone 16), and ND, SD (Zone 14).  About 80% of my area 
of interest is in Zone 15.
I also came across a thread from Feb97 that suggested making symbolic links 
of mapsets and then running  g.mapsets.  What you suggest sound more 
straightforward.  Would these procedures be equivalent?


>>Assuming I can figure that out, do I use r.mask to remove the background 
>>from each of these maps?
>
>You probably do not need to mask. I am guessing that the background is NULLs?

The background is set to "0". Would a NULL be transparent? Maybe use: 
r.null map="name" setnull=0


>--
>Richard Greenwood
>www.greenwoodmap.com


Thanks for your help.

Martin