[GRASS-user] GRASS raster curvature analysis type

[Markus Metz]

On Tue, Sep 13, 2016 at 5:48 PM, Markus Neteler <neteler at osgeo.org> wrote:
> On Tue, Sep 13, 2016 at 4:02 PM, Anna Petrášová <kratochanna at gmail.com> wrote:
>> On Tue, Sep 13, 2016 at 7:58 AM, Helmut Kudrnovsky <hellik at web.de> wrote:
>>> georges wrote
>>>> Hello,
>>>>
>>>> I would like to know whether raster curvature analysis in GRASS
>>>> is Gaussianor Mean curvature analysis?
>>>> https://en.wikipedia.org/wiki/Gaussian_curvature
>>>> https://en.wikipedia.org/wiki/Mean_curvature
>>>>
>>>> This GRASS 7.2 manuals page mentions that raster curvature analysis can be
>>>> conducted in direction of steepest slope and in the direction of the
>>>> contour tangent, therefor distinguishing two curvature options: profile
>>>> and tangential.
>>>>
>>>> Still are these two Gaussian or Mean curvatures?
>>>>
>>>> Thank you for the reply.
>>>
>>> I can't tell you directly which algorithm is used.
>>>
>>> fortunately GRASS GIS is open source; so maybe have a look at the source
>>> code to check:
>>>
>>> r.slope.aspect:
>>>
>>> https://trac.osgeo.org/grass/browser/grass/trunk/raster/r.slope.aspect/main.c
>>>
>>> or
>>>
>>> r.resamp.rst
>>>
>>> https://trac.osgeo.org/grass/browser/grass/trunk/raster/r.resamp.rst/main.c
>>>
>>> HTH
>>
>> also r.param.scale:
>> https://trac.osgeo.org/grass/browser/grass/trunk/raster/r.param.scale/

IIUC, Gaussian and Mean curvatures are based on principal curvatures.
Principal curvatures in turn are calculated for an orthonormal basis.
r.param.scale calculates different principal curvatures for different
bases (z-axis and the surface normal vector). You can obtain Gaussian
or Mean curvatures from these principal curvatures.

Markus M

>
>
> You find the formulas used for the r.slope.aspect and r.resamp.rst
> implementations in the GRASS book, 3rd edition, 2008, Springer,
> Appendix pages 371-376.
>
> Best,
> Markus
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user