[GRASS-user] Strange r.slope.aspect output of Aster dem : slope calculations

[Vaclav Petras]

On Fri, Dec 20, 2013 at 12:37 PM, Markus Neteler <neteler at osgeo.org> wrote:

> On Fri, Dec 20, 2013 at 4:54 PM, manuel.martin
> <manuel.martin at orleans.inra.fr> wrote:
> > Hi all,
> > I just computed the slope using r.slope.aspect on the Aster data over the
> > full French territory, and as a result got large artefact stripes on a
> south
> > west-north east axe? When could it come from (inadequate re-projection,
> the
> > slope routine or the aster data)?
>
> Do you use these data in their original projection?
>
> Hi, I would say that problem is in the DEM. Maybe the DEM needs some
cleanup (such as smoothing by r.neighbors). Using lower resolution (less
detailed) may help (r.resample probably needed). Blue stripes are probably
places where the elevation changes a lot and thus creating slopes.

So, using EU-DEM might be a good solution.

Vaclav

BTW:
> you may use the new EU-DEM: Digital Surface Model at 25m
>
> I made some screenshots at:
> http://courses.neteler.org/eu-dem-new-digital-surface-model-at-25m/
>
> and continue to use it for various applications:
>
> http://courses.neteler.org/using-the-25m-eu-dem-for-shading-openstreetmap-layers/
>
> (r.sun based analysis coming soon)
>

> Markus
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