[GRASSLIST:2369] Fun with gdal - Follow-up

[SWlab]

Hello,
I eventually installed the 2004/01/23 CVS version of grass 5.3 to solve the 
(in)famous segfault pb in gdal (cf message 2333). Thanks for the tip, it 
solved my problem, I'm now able to import my dem maps. And now, for a GIS 
question:
I need to get the topography of an area at the intersection of 4 USGS 7.5 
quadrangles. My four individual DEMs are in UTM18, NAD27. I defined a region 
large enough to cover the four quadrangles at once, UTM18 NAD27 also. What's 
the best option ?
1. To import each DEM in my current region through gdal, and use r.patch ?
2. To create a new location for each DEM with gdal, then import each DEM from 
its new location to my current region (and then running r.patch...) ?

I tried the two options, and computed a difference: there's a difference 
indeed,from +10 to -15 on the picture I join. Which method should I follow ?

And thread hijacking:
When I patch the 4 DEMs in a new one, some cells are missing (undefined). Is 
there a simple algorithm to fill for the missing data ?

Thanks a lot for any comment/idea
P.
-- 
Soil & Water Laboratory
Dept. of Biological & Environmental Engineering
Cornell University
ITHACA, NY 14853
Tel: (607)255.2463
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