[GRASS-dev] r.mask: odd behavior?

[Markus Metz]

On Sun, Nov 19, 2017 at 9:19 PM, Veronica Andreo <veroandreo at gmail.com>
wrote:
>
> Hi devs,
>
> I found that r.mask does not behave as I would expect and I would really
appreciate some clarification.
>
> The issue is the following: I apply a mask, then I do some processing, I
remove the mask and when I display the resulting map, all the pixels were
processed. I would expect that those pixels that I masked were treated as
NULL and not considered exactly as the message says:
>
> "All subsequent raster operations will be limited to the MASK area.
Removing
> or renaming raster map named 'MASK' will restore raster operations to
> normal."

A MASK affects only reading raster data, not writing raster data. Therefore
r.mapcalc "test = 1" will always produce a map without NULL cells.

Markus M

>
> Otherwise, what's the point of applying a mask?
>
> This is an example with NC:
>
> g.region raster=landcover_1m -p
> r.category landcover_1m
> r.mask raster=landcover_1m maskcats="1 thru 6"
> d.mon wx0
> d.rast landcover_1m
> r.mapcalc "applied_mask = 1"
> r.mask -r
> d.erase
> d.rast applied_mask <<-- everything is there, no holes...
>
> The only operation that gave me what I would expect when I apply a mask
was:
> r.mapcalc expression="applied_mask=1-MASK"
>
> Can someone, please, test/clarify this?
>
> thanks much in advance!
> Vero
>
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