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List:       qgis-developer
Subject:    AW: [Qgis-developer] Raster based terrain analysis with QGIS
From:       "Hugentobler  Marco" <marco.hugentobler () karto ! baug ! ethz ! ch>
Date:       2009-08-22 19:32:30
Message-ID: 04DA676AA276F045B32D0F95783D78449489B1 () EX6 ! d ! ethz ! ch
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Hi Paolo

> Does it work with any raster source?

It should work with every GDAL supported source. Currently it always takes the first \
band as input (assuming that the terrain rasters are usually single band rasters).

> It will be interesting to compare the results with analogous modules from GRASS.

Yes, slope and aspect can be compared with results from GRASS commands \
(r.slope.aspect). I tested the slope and found that, for my test area, the results \
are identical (as they also used Horn's algorithm for derivative estimation). One \
small difference is that r.slope.aspect fills the border cells with null values while \
the raster terrain plugin tries to estimate these too.

Performance comparison is surely also interesting. Slope calculation on my test \
raster (1.6 GB large GeoTiff) took 2min5s with the raster plugin (saved to GeoTiff). \
The same raster, imported into grass with r.in.gdal, took 3min12s to process with \
r.slope.aspect. But this is not a systematic evaluation at all, just a single test. \
It surely depends also on the raster format you use for reading/writing in the \
plugin.

Regards,
Marco 


-----Ursprüngliche Nachricht-----
Von: Paolo Cavallini [mailto:cavallini@faunalia.it]
Gesendet: Sa 22.08.2009 08:43
An: Hugentobler  Marco
Cc: qgis-developer@lists.osgeo.org
Betreff: Re: [Qgis-developer] Raster based terrain analysis with QGIS
 
Hugentobler Marco ha scritto:

> I thought that this plugin could ev. go into the upcoming analysis library of
> QGIS. Btw. are there any objections on merging the branch with the analysis
> library after the release of 1.2 and using the library for the interpolation
> and raster terrain plugin? fTools will come later I think as it probably is a
> lot of work to port the python code to C++...

+1 Thanks Marco.
Does it work with any raster source?
It will be interesting to compare the results with analogous modules from GRASS.
All the best.
-- 
Paolo Cavallini: http://www.faunalia.it/pc

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