[GRASS5] 0 != no data

Justin Hickey jhickey at hpcc.nectec.or.th
Sun Jun 10 22:09:56 EDT 2001


Hi Bob

Bob Covill wrote:
> 
> Justin Hickey wrote:
> >
> > Hi all
> >
> > Recently we experienced a problem with using aerial photographs as
> > raster maps. The photographs are grayscale and thus range in value 
> > from 0 to 255. Here 0 is a valid CELL value, however, Grass 5
> > treated it as a "no data" value. So, displaying our maps, these
> > white areas appeared (where they should have been black) that were
> > displayed as "(Null) no data" in d.what.rast. Initially, we thought
> > that the data had been corrupted somehow, but it was only Grass
> > interpreting 0 as "no data".
> >
>
> Zero should (hopefully) be imported as zero. I wonder if the problem 
> is actually with the import program. What program did you use to
> import the images? Maybe as a test, try converting an image to
> another supported format (eg. TIFF, SunRaster) and re-importing to
> see how the zeroes are handled.

The map was originally imported using r.in.tif.

-- 
Sincerely,

Jazzman (a.k.a. Justin Hickey)  e-mail: jhickey at hpcc.nectec.or.th
High Performance Computing Center
National Electronics and Computer Technology Center (NECTEC)
Bangkok, Thailand
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