[Qgis-developer] Fwd: Re: [GRASS-dev] GRASS and sextante

Paolo Cavallini cavallini at faunalia.it
Tue Jun 5 04:56:25 PDT 2012


-------- Messaggio originale --------
Oggetto: Re: [GRASS-dev] GRASS and sextante
Data: Tue, 5 Jun 2012 13:36:11 +0200
Mittente: Markus Metz <markus.metz.giswork at googlemail.com>
A: Benjamin Ducke <benducke at fastmail.fm>, Paolo Cavallini <cavallini at faunalia.it>
CC: GRASS developers list <grass-dev at lists.osgeo.org>

Benjamin Ducke wrote:
> Theoretically, it wouldn't be very hard to read the labels
> from the mapset in which SEXTANTE is storing the (temporary)
> GRASS datasets; they are saved as plain ASCII there.
> However, the host GIS for SEXTANTE must then somehow deal
> with this additional data in some useful way (e.g. via a
> virtual raster attribute table).

An alternative would be to make use of the GDAL raster attribute table
in both GRASS and QGIS, with the benefit that reading labels for other
raster maps imported with GDAL would also be supported.

IIUC, QGIS is currently using GDALGetRasterCategoryNames() which has
very limited functionality and supports only integer maps. In a GDAL
raster attribute table, as with GRASS-internal categories, floating
point values and data ranges are supported, e.g.

min=358.5, max=359.5, name=359 degrees ccw from east

A GDAL raster attribute table would also solve the problem of
importing/exporting color rules for floating point data types.

Markus M

> On Mon, Jun 4, 2012, at 16:45, Paolo Cavallini wrote:
>> Hi all.
>> Now working on sextante interface to grass. One problem I'm finding is:
>> - GRASS raster can have labels (very convenient, e.g. r.param.scale saves
>> feature
>> names along with categories)
>> - when saving to TIFF, these are stripped
>> - as a consequence, the flow DTM>Features raster>Feature vector strips
>> the
>> categories, and data are lost.
>> Any way of keeping them? Of course we can Use raster values as
>> categories, but
>> keeping the labels would be much better. One way would be to pipe
>> directly the two
>> GRASS commands, without exporting in between, but this is not implemented
>> yet.
>> All the best.
>> --
>> Paolo Cavallini - Faunalia
>> www.faunalia.eu
>> Full contact details at www.faunalia.eu/pc
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