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

[Paolo Cavallini]

I'm forwarding here comments from Markus Neteler.
All the best.

> --------  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.

> BTW, I'm unsure about the G7 support in the Browser: could someone check
> thoroughly?
>
>> If no one is interested in making the port of the plugin for GRASS 7, we
>> could try through a crowdfounding initiative. Who was behind the initial
>> creation of GRASS plugin?
>
> Yes, I have been talking about that. Radim did most of the work on the
> plugin. If he (or eventually others) are available, a crowdfounding
> initiative could be appropriate.

Yes, it would be great to get the plugin updated as well.

>> I've been checking the differences and they are indeed few. Please see
>> the spreadsheet attached.
>
> Obrigado for this.
>
>> Some commands seem that were adaptations of other algorithms, made for
>> Processing, as they are not in the 6 manual, or in the 7:
>> r.cost.full.raster, r.drain.coordinate, r.terraflow.short,
>> v.surf.rst.cvdev.line, v.surf.rst.line, v.transform.pointsfile.
>
> Yes, these are adaptations of the original commands, in order to make
> them more usable from QGIS.

Update to GRASS GIS 7 should not be a lot of work, see below.

>> Others seem that have been removed from GRASS 7 (r.average, r.bilinear,
>> r.bitpattern, r.surf.idw2), as they are not in the GRASS 7 manual.

It is all documented in the release notes:

http://trac.osgeo.org/grass/wiki/Grass7/NewFeatures#Replacedandremovedmodules
[...]
raster:
- r.average: merged into G7:r.statistics, G7:r.stats.zonal,
G7:r.stats.quantile
- r.bilinear: merged into G7:r.resamp.interp
- r.bitpattern: G7:r.mapcalc (&&& and | | | operators) + G7:i.modis.qa
offer the same and more functionality
[...]
- r.surf.idw2: moved to Addons (install with G7:g.extension)
- r.terraflow.short (merged into FP version G7:r.terraflow is sufficient)
[...]

>> There are five that seem important to me, which are in GRASS 7, in
>> Processing GRASS 6, but not in Processing GRASS 7: r.out.xyz, r.ros,
>> r.spread, r.univar, v.kernel.
>>
>> Finally, there are two commands that are on GRASS 7 and were not in 6:
>> r.viewshed (which replace r.los) and r.relief (which replace
>> r.shaded.relief).
>
> Overall, I think these are minor issues. If someone really miss them,
> they can ask, and we can add them.

I updated "Processing" accordingly, so you can see the needed changes
from the changelog.
Or simply here:

http://trac.osgeo.org/grass/wiki/Grass7/NewFeatures#Optionschanges

Best regards,
Markus

-- 
http://courses.neteler.org
http://gis.cri.fmach.it/neteler/

Next GRASS GIS 7 courses: Berlin, 16 +17 March 2015
http://courses.neteler.org/next-training/



> All the best, and thanks again.
> --
> Paolo Cavallini - www.faunalia.eu
> QGIS & PostGIS courses: http://www.faunalia.eu/training.html
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