[Qgis-developer] Fwd: Re: Re: QGIS and GRASS 7.0.0

[Vaclav Petras]

On Tue, Feb 24, 2015 at 6:19 AM, Paolo Cavallini <cavallini at faunalia.it>
wrote:

> > --------  Messaggio Inoltrato --------
> > Oggetto: Re: [Qgis-developer] QGIS and GRASS 7.0.0
> > Data: Tue, 24 Feb 2015 08:08:18 +0100
> > Mittente: Paolo Cavallini <cavallini at faunalia.it>
> > Organizzazione: Faunalia
> > A: Pedro Venâncio <pedrongvenancio at gmail.com>
> > CC: qgis-developer <qgis-developer at lists.osgeo.org>
> >
> > Olá Pedro,
> >
> > Il 23/02/2015 22:06, Pedro Venâncio ha scritto:
> >
> >> Despite the great advantages of GRASS commands in Processing, I think
> >> that the GRASS plugin still plays an important role and is an excellent
> >> interface for GRASS. For those who still like to use the paradigm of
> >> locations, mapsets and the GRASS topological model, GRASS plugin is very
> >> important, because then it allows to use all QGIS tools, for example, to
> >> create layouts using the Composer, etc.
> >
> > Agreed. Moreover, the overhead of importing/exporting data for each step
> > of a complex analysis puts GRASS algs to a disadvantage for Processing
> > users.
>
> The overhead is not necessarily needed in case of raster maps:
>
> #### Workflow example:
> # register GeoTIFF file in GRASS GIS database (no import but direct link):
> r.external input=tempmap1.tif output=modis_celsius
>
> # define output directory for files resulting from GRASS calculation:
> # i.e. GRASS GIS writes directly a GeoTIFF file here, no GRASS DB storage
> r.external.out directory=$HOME/gisoutput/ format="GTiff"
>
> # perform calculation (here: extract pixels > 20 deg C) and
> # write output directly as GeoTIFF:
> r.mapcalc "warm.tif = if(modis_celsius > 20.0, modis_celsius, null() )"
>
> # cease GDAL output connection and turn back to write GRASS raster files:
> r.external.out -r
>
> # use the result elsewhere
> qgis $HOME/gisoutput/warm.tif
> #### END Workflow example:
>
> This approach could be used in "Processing" as well. Or in a WPS context
> etc.
>

Hi,

see also GRASS GIS (+QGIS?) GSoC 2015 idea for further discussion on that
topic:

http://trac.osgeo.org/grass/wiki/GSoC/2015#Neweasy-to-usecommandlineinterfaceforGRASSGIS

>From the QGIS Processing source code, I actually got an impression that
this approach is already used for rasters.

Vaclav
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