I have calculated slope and aspect using the DEM (Terrain models) GUI in QGIS Essen. I was also able to calculate the profile and tangential curvature using the toolbox r.slope.aspect. I was wondering if anyone can point me in the direction of documentation that describes the algorithm used to calculate these terrain parameters. I would like to know HOW they are calculated not how to use the plugins. For example, I would like to now how large of an averaging window the program uses, how it choses direction, what it does on the edges of a raster, etc.


There is good documentation on all aspects of GRASS internals, including references to literature. So see the documentation on r.slope.aspect. Unfortunately I find it difficult to get this level of documentation for the methods exposed in the DEM/Terrain Models QGIS GUI. I'd recommend sticking entirely to GRASS if these implementation details are important to you; but perhaps someone else has a link to the QGIS implementation, it's probably all documented in GDAL.

  • If one is really keen and inquisitive, it can often be found in the source code, hence open source; for both GRASS and QGIS, GDAL, etc. – SaultDon Oct 19 '16 at 1:31
  • Agreed, but GRASS's comprehensive summaries of higher-level information is a big mark in its favour. – alphabetasoup Oct 19 '16 at 1:33
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    For sure, that's why I just added a comment. I've found GRASS manual pages and the wiki extremely educational. – SaultDon Oct 19 '16 at 1:36
  • As an extra, there are now the direct links to the source code starting from GRASS GIS 7.2.0 :-) See e.g. at page bottom of grass.osgeo.org/grass72/manuals/r.slope.aspect.html – markusN Oct 20 '16 at 18:26
  • There is great documentation of all GIS processing in a book entitled 'Geomorphometry: Concepts, Software, Applications' from the Developments in Soil Science series (33). I've found it to be very informative and helpful! – Alex Dec 14 '16 at 19:18

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