[GRASS-user] extract slope lower than 25 meters ?

GRASS GRASS user
,
1

Good morning, I have to extract slope lower than 25 meters. But i’m working with SRTM raster DEM 30 meters resolution… 1/ Is there a tool with qgis in order to extract slope values? 2/ According to you, is it possible to extract 25 meters slope values with srtm 30 meters. if it is not the case, do you know another way? Another DEM more acurate for instance? Thank you very much.

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2

Hi,
generally we cinsider slope an angle measure. What do you mean with slope under 25 meters?
In GRASS you can use r.slope.aspect to obtain the slope map.

This is the GRASS mailing list, not QGIS’s. Anyway you can use many GRASS commands through the GRASS plugin in QGIS. Within the Processing toolbox look for “slope” keyword using the Filter tool at the top of the toolbox

giovanni

Il 03/apr/2015 09:46 “image93” <lcelati@cci-paris-idf.fr> ha scritto:

Good morning, I have to extract slope lower than 25 meters. But i’m working with SRTM raster DEM 30 meters resolution… 1/ Is there a tool with qgis in order to extract slope values? 2/ According to you, is it possible to extract 25 meters slope values with srtm 30 meters. if it is not the case, do you know another way? Another DEM more acurate for instance? Thank you very much.

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On 03/04/15 09:45, image93 wrote:

Good morning, I have to extract slope lower than 25 meters. But i'm
working with SRTM raster DEM 30 meters resolution... 1/ Is there a tool
with qgis in order to extract slope values? 2/ According to you, is it
possible to extract 25 meters slope values with srtm 30 meters. if it is
not the case, do you know another way? Another DEM more acurate for
instance? Thank you very much.

You can always interpolate from 30m resolution data to an estimation of higher-resolution data, for example using v.surf.rst. However, this will always only be an estimation, not the real altitude data. If you want real slope you have to find a higher-resolution DEM. Which region are you working on ?

For France, IGN-France has higher-resolution products.

Moritz

4

On 03.04.2015 08:45, image93 wrote:

Good morning,I have to extract slope lower than 25 meters. But i'm working
with SRTM raster DEM 30 meters resolution...

See also: <https://geoservice.dlr.de/web/maps/srtm:x-sar&gt; and a relevant document <http://www.dlr.de/eoc/en/Portaldata/60/Resources/dokumente/7_sat_miss/srtm_products_en.pdf&gt;\. You might be lucky and you region lies inside what is already covered.

Nikos

5

Hello,
Thank you.
Indeed, my region lies inside what is already covered. But do you know how
to get the data?

Thanks.

--
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6

* image93 <lcelati@cci-paris-idf.fr> [2015-04-09 19:08:10 -0700]:

Hello,
Thank you.
Indeed, my region lies inside what is already covered. But do you know how
to get the data?

<http://centaurus.caf.dlr.de:8080/free_SRTM_X-band_data.html&gt;

Nikos