AW: [Qgis-developer] Raster based terrain analysis with QGIS

[Hugentobler Marco]

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 at faunalia.it]
Gesendet: Sa 22.08.2009 08:43
An: Hugentobler  Marco
Cc: qgis-developer at 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