[GRASSLIST:2247] Importing DEMs and concatenating them

[Rich Shepard]

  I have a 3x3 array of DEMs (each covers the area of a 7.5-minute
topographic quad map), and I'm using r.in.gdal to translate them from SDTS
format to GRASS-5. After the required step of exporting, changing the
'-32766' for missing data to '0', and re-importing, the maps show up in
their proper relative position in a region that encompasses all 9 maps.

  However, when I try to use r.patch to staple them together and display the
resulting map, all I see is the first one in the input list with the white
background masking the others (if they're there).

  Perhaps the problem is that I'm not sure how NULL (no data) is represented
in GRASS-5. Is it the asterisk I see in the exported ASCII files? According
to the r.patch man page, the second (and later) input files attempt to
replace NULL value with actual values; if the SDTS NULL value of -32766 is
replaced with 0, then of course, r.patch won't work.

  Correct?

TIA,

Rich

Dr. Richard B. Shepard, President

                       Applied Ecosystem Services, Inc. (TM)
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