[GRASS-user] Re: raster MASKs;
was [GRASS-dev] interferring ovewrite flags
hamish_nospam at yahoo.com
Mon Oct 2 03:37:36 EDT 2006
Michael Barton wrote:
> Right. I understand, even if I didn't phrase it that way. Does this
> happen for any r.mapcalc processing using the same procedures or just
> ones in which MASK is the result? Also, is it always an "and" or can
> you also get the effects of an "or"? Definitely a 'gotcha' to watch
> out for. I'm concerned especially because we are doing a lot of
> iterative r.mapcalc processing in scripts and this could be a problem.
The MASK is generally applied when a row of input data is read from the
A module scan specifically ask to ignore the MASK, but the vast vast
majority of raster modules process data by row (to save memory), and use
G_get_raster_row() to do that.
G_get_raster_row_nomask() is the non-masking version. Things that use it:
d.rast elevation.dem # displays with holes
r.mapcalc one=1 # full coverage once MASK is removed
r.mapcalc two=elevation.dem # holes once MASK is removed
the numeric mapcalc cmd hasn't read a map from the disk, so in fact it
is a solid block. The "two" map has read, so in fact contains holes.
If the "one" map is displayed with a MASK in place, it appears to have
holes in it, but these are introduced when d.rast loads the map to
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