Thank you for this prompt reply. One additional
question. Is there any quick way to get a hipsometric curve or
area values between different altitude intervals from a DEM
representing my basin?
I don't know about quick, but here are a few GRASS modules that you
might find helpful.
r.reclass
can create a new raster from the original DEM broken into steps that
you specify. So you could create a raster with elevation steps of,
say, 50 meters. Now run r.stats -a on
that raster and you'll get a list of the total area for each value.
This list could be imported into any other software (spreadheet) to
calculate the accumulated areas for each elevation step.
Another option could be to use r.contours to create contour
lines at whatever interval is suitable. (There is also the GDAL Tool
gdal_contour
in QGIS, under Raster->Extraction). Now merge the contour lines
with the basin boundary to form closed boundaries around each
elevation "strip", and convert into polygons. And finally, in GRASS
use the v.rast.stats
module to calculate several statistics for each elevation polygon.
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.
The units should be the units of the coordinate system. I
think that if you want altitudes and lengths in meters,
you'll have to project both the raster and the line features
to a projected CRS with meters as units.
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 as it gives me back only one cell as the basin
and not a combination of cells which could form a real
basin. Any tutorial or video in how to use this command?
Perhaps the problem is that the outlet point must fall
exactly on a stream. There's a trick using v.distance to
find a drainage point exactly on the stream, described here:
First add two columns to the streams layer: outlet_x,
outlet_y. Now use v.distance with your outlet point as the
"from" parameter, and the stream as the "to" parameter. Set
the upload parameter to "to_x,to_y" and the column parameter
to "outlet_x,outlet_y". Now after you run, you should get
the X,Y coordinates of a point *on the stream* nearest to
your planned outlet point. Use those coordinates in your
r.water.outlet command, and you should get the full drainage
area.
