[GRASS-dev] [GRASS GIS] #2032: r.mapcalc does not always respect MASK

[Paulo van Breugel]

On Tue, Jul 16, 2013 at 8:26 PM, GRASS GIS <trac at osgeo.org> wrote:

> #2032: r.mapcalc does not always respect MASK
>
> -------------------------+--------------------------------------------------
>   Reporter:  pvanbosgeo  |       Owner:  grass-dev@…
>       Type:  defect      |      Status:  closed
>   Priority:  normal      |   Milestone:  7.0.0
>  Component:  Raster      |     Version:  unspecified
> Resolution:  invalid     |    Keywords:  r.mapcalc
>   Platform:  Linux       |         Cpu:  Unspecified
>
> -------------------------+--------------------------------------------------
>
> Comment(by glynn):
>
>  Replying to [comment:2 pvanbosgeo]:
>  > OK, thanks, I didn't know that / hadn't read that part of the manual
>  carefully enough. Perhaps not something that the user will encounter
>  often, but nonetheless, it is something I can see others might overlook as
>  well when using r.mapcalc. Perhaps a short note of this can be added to
>  the r.mapcalc help file (which is where I looked to see where my
>  expectations of the behavior of r.mapcalc were wrong)?
>
>  The behaviour isn't specific to r.mapcalc. Except for a few special cases,
>  the MASK behaviour isn't implemented by the individual modules, but by the
>  raster I/O library. You can observe the same behaviour with e.g.
>  r.neighbors.
>
  The correct place to document this behaviour is wherever the MASK
>  behaviour is described, e.g. the rasterintro manual page and the r.mask
>  manual page. FWIW, the first sentence of the DESCRIPTION section of the
>  r.mask manual page (after the summary) is:
>  {{{
>  The MASK is only applied when reading an existing GRASS raster map,
>  for example when used in a module as an input map.
>  }}}
>

Just to clarify, of course the behaviour should be mentioned in the
mentioned manual pages. I merely suggested to add a reminder for this part
of the behaviour of MASK in the help file of r.mapcalc.

The reason I think such a reminder might be helpful is that modules like
r.neighbors always require an existing map as input and therefore the MASK
will normally be respected. For most other modules there is no reading of
an input map and thus the MASK has normally not influence (e.g.,
r.surf.fractal). For r.mapcalc, both are possible.

BTW, is the mentioning in e.g., the help file of r.neighbor that it
respects existing MASK not just that; a (useful imho) reminder of the
default behaviour mentioned in the raster intro page, viz.
"Raster input maps are automatically masked if a raster map named MASK
exists."?

Anyway, just to clarify my initial suggestion. I probably will not forget
this behaviour anyway :-).


>
> --
> Ticket URL: <http://trac.osgeo.org/grass/ticket/2032#comment:3>
> GRASS GIS <http://grass.osgeo.org>
>
>
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