[Qgis-user] Slope aspect curvature

[Nicolas Cadieux]

Hi, 
I would use the Grass algorithm or Gdaldem instead.  It is also found in the processing plugin using the batch mode. You can also script it in python but that should not be necessary. 
I am not sure about the Saga algorithm, and I am far from a computer but my guess is that your layer CRS is in Long/lat but the z is in meters like the SRTM or Aster GDems giving you different units for x,y and z. 
In many cases, that will give you results like those you are getting. You need to adjust the z scale.  
This is from gdal: 
" slope 
This command will take a DEM raster and output a 32-bit float raster with slope values. You have the option of specifying the type of slope value you want: degrees or percent slope. In cases where the horizontal units differ from the vertical units, you can also supply a scaling factor. 
The value -9999 is used as the output nodata value. 
The following specific options are available : 
-p :if specified, the slope will be expressed as percent slope. Otherwise, it is expressed as degrees-s scale:ratio of vertical units to horizontal. If the horizontal unit of the source DEM is degrees (e.g Lat/Long WGS84 projection), you can use scale=111120 if the vertical units are meters (or scale=370400 if they are in feet)" 
http://www.gdal.org/gdaldem.html 
Nicolas Cadieux M.Sc. 
Les Entreprises Archéotec inc.  
8548, rue Saint-Denis Montréal H2P 2H2 
Téléphone: 514.381.5112  Fax: 514.381.4995 
Le 2014-12-28 09:29, "nagyrobi_r [via OSGeo.org]" <ml-node+s1560n5179348h49 at n6.nabble.com> a écrit : 

	Hey! Im using Qgis 2.6 on a 64 bit windows platform. I need to process 140 DEMs and i would like to make an automatic process to calculate Slope aspect curvature. In order to do the script i need the command itself for the slope aspect curvature. I have tried :
import processing
processing.runalg("saga:slopeaspectcurvature", 'D:/data/dem.tif', 1,'D:/data/slope/dem_slope.tif',None, None, None, None)
the process creates a slope map at my given path, but the value of ranges is between 0 and 1. As i know it should be between 0-90 degrees. if i execute it from the toolbox, the range is different( even if percentages are used). in any case the values are totally different. Because the slope has a different range every other map(aspect, curvatures) have bad values.
Other ways to compute slope aspect from console or python script? Any suggestions what i am missing or doing wrong?
Thank you a lot!

	
	
	
	
	
	
	
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