Mosaicking 7.5-Minute DEMs Across UTM Zones

Darren S. Embry h2edhdse at
Thu Jul 27 16:16:32 EDT 1995

Hi, Folks!

I am having problems trying to mosaic together some 7.5-minute USGS
DEMs which lie in different UTM zones (these are the ones which have a
30-meter resolution and internally store the UTM coordinates; I use dd
and m.dem.examine to extract them).

As an example of how the problem manifests itself and how I discovered
this problem, let us take the Piqua and Cowan 7.5-minute quadrangles
in Kentucky, which are right next to each other.  (In case you don't
have access to an index, these are bounded on the north by 38:30:00N
and on the south by 38:22:30N; Piqua lies directly to the west of 84W
in zone 16; and Cowan lies directly to the east in zone 17.)  My
region is currently in zone 16; and when I plot the raster for Piqua,
it's plotted in the right place; but when I plot the one for Cowan
it's somewhere in Illinois (shifted 6 degrees to the west, I suppose)
because GRASS doesn't know for some reason that Cowan is actually in
zone 17!

I was hoping there was an ``r.transform'' command, but no such luck :(
so is there some other way I can alleviate this problem, other than
using the 1-by-2-degree DTED files (which don't mosaic together very
well at all)?

					-- Darren

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