[GRASS-user] Problem with r.basin in grass7

[Markus Neteler]

Hi Andrea,

On Thu, Nov 6, 2014 at 5:46 AM, Andrea Timmermann <timmermann at gmx.at> wrote:
> Hi !
>
> I downloaded the 5-Nov Grass and also updated all the addons extensions I
> use.
>
> When I run:
> "r.basin map=map at Elevation prefix=o coordinates=-71.10394196,43.9865230801
> threshold=19005 dir="C:\\Users\\Andrea\\Basins"
>
> I get:
> "...
> Building topology for vector map <o_map_outlet at Elevation>...
> Registering primitives...
> One primitive registered
> One vertex registered
> Building areas...
> 0 areas built
> 0 isles built
> Attaching islands...
> Attaching centroids...
> Number of nodes: 0
> Number of primitives: 1
> Number of points: 1
> Number of lines: 0
> Number of boundaries: 0
> Number of centroids: 0
> Number of areas: 0
> Number of isles: 0
> ------------------------------
> An ERROR occurred running r.basin
> Please try with another pairs of outlet coordinates"

I have just now submitted a bunch of fixes for r.basin, see

http://trac.osgeo.org/grass/changeset/62672

Please try again...

...
> And about the known issues at the same page: "r.basin hasn't been designed
> for working in lat/long coordinates. This means that if you are working in
> lat/long coordinates, you need to reproject your map first in order to apply
> the tool".
>
> The DEMs I am using have a resolution of 0.33 degrees

Do you mean 33 arcseconds? Otherwise it would be something like 30km pixels :-)

> and when I reproject
> them (projection: 3 (Latitude-Longitude); zone: 0; datum: nad83; ellipsoid:
> grs80), the areas covered by the DEMs files vary depending on the longitude:
> the surface covered by one file is larger near the equator than closer to
> the poles. So I think this means that the cell resolution of my reprojected
> map is larger near the poles than at the equator? If so, it would only make
> sense to compare the morphometric parameters for catchments at a similar
> latitude I think... Am I right? I am a bit confused with this ...

Perhaps you can find a DEM in a metric projection for your study area
which would save you some times?

Best
Markus