[Qgis-user] Problems with profile from line altitude values + r.water.outlet command

[Mikhail Titov]

Jaime Palalane <mitasjp-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org> writes:

> I am trying to use qGIS to characterize a hydrographic basin but I am
> facing problems with the profile from line tool as it is giving an
> unique altitude value for my rivers and lengths in grades. I would
> like to have them in SI units. I would appreciate some tips in how to
> solve this problem.

You should project your raster first into something like UTM.

> I am also trying to use the r.water.outlet command to define a basin
> draining to a specific point of a stream in raster format but without
> success

Remember to project raster!

> as it gives me back only one cell as the basin and not a combination
> of cells which could form a real basin.

You are off the stream. Make sure you place your outlet _exactly_ on
the stream. You can use flow accumulation (AKA upslope contributing
area) to manually position your outlet better. GRASS 7 has module to
snap outlet to stream [1].

But even better approach is to use TauDEM via sextante [2]. You can easily
snap your outlets to stream with it and more tools are at your disposal.

> Any tutorial or video in how to use this command?

[3]

[1] http://svn.osgeo.org/grass/grass-addons/grass7/raster/r.stream.snap/
[2] http://hub.qgis.org/projects/sextante-taudem
[3] http://hydrology.usu.edu/taudem/taudem5.0/documentation.html

-- 
Mikhail