[GRASS-user] how to g.region

[Hamish]

Raffaello Brondi wrote:
> >> i'm using GRASS 6.2 for developing a Web Processing Service.
> >
> > Have you seen Jachym's PyWPS?
> >   http://pywps.wald.intevation.org
> >   
> yes i saw it..but unfortunately i have to develop the service using
> Java.

Have you seen jGRASS?  http://www.jgrass.org/

Raffaello:
> >> One of the operations offered by the service takes two raster maps
> >> as inputs.
> >> The raster map resulting from this operation would have different 
> >> spatial extents based on the input maps: the result would have the 
> >> extent equal to the extent of one of the two input maps, or equal to
> >> the union of the extents of the two input maps or equal to the
> >> intersection of the extents of the two raster maps.
> >> In order to develop the service i need to manage these four cases by 
> >> changing the GRASS region.
> >> Supposing that the input rasters are "raster1" and "raster2", the 
> >> possible configurations are:
> >>
> >>    1. region = raster1 --> g.region rast=raster1
> >>    2. region = raster2 --> g.region rast=raster2
> >>    3. region = the union of raster1 and raster2 --> g.region 
> >> rast=raster1,raster2
> >>    4. region = the intersection of raster1 and raster2 --> ?
> >>
> >>
> >> As far as i see, using the g.region command, there is no way to
> >> specify the last point except to manually set the nord,sud,ovest and
> >> east values, but unfortunately i can not use this way.
> >> Is there any other command in GRASS that i can use instead of
> >> g.region to set the current region as the intersection of two
> >> rasters? 
> >

Hamish:
> > This is not very efficient, and more like 'g.region zoom=', but you
> > could do:
> >
> > g.region rast=map1,map2
> > r.mapcalc 'intersect= if(!isnull(map1) && !isnull(map2), 1, null())'
> > g.region zoom=intersect
> > g.remove intersect
Raffaello:
> This is the solution i need :).

Wolf:
> g.region rast=raster1
> g.region -p (parse the output, into rast1north, rast1east, rast1west,
> rast1south, etc)
> g.region rast=raster2
> g.region -p (parse the output, into rast2north, rast2east, rast2west,
> rast2south, etc)
> g.region north=(min of rast1north, rast2northe) etc for other
> parameters.

Raffaello:
> Your solution is a good one but the problem is the overhead it
> introduces. Since i can't (or maybe i'm not able to :( ) interact
> directly with GRASS using Java, i would need to make 4 files
> reading/writing.

Running g.region twice is going to have way less overhead than running
r.mapcalc, especially if the maps are of a reasonable size.


GRASS now has SWIG bindings to help closely link GRASS's libgis etc.
into higher level languages than C/C++. Right now we have some
parts in place for perl & python, but a motivated contributor could
add java to that list. look in the swig/ directory in the 6.3 source code.
  http://www.swig.org/Doc1.3/Java.html


Hamish