[GRASS-user] Re: Defining Partial Drainage Basin

[Rich Shepard]

On Wed, 10 Feb 2010, Micha Silver wrote:

> A quick tip regarding r.water.outlet (you may have noticed this already)
> The module creates a new raster covering the whole analysis region with
> two possible values: 1 for all cells draining into the outlet, and 0
> everywhere else. If you do r.to.vect straightaway, you?l get a vector
> containing two polygons... I always run r.null setnull=0 on the
> r.water.outlet result first. This insures that r.to.vect leaves you with
> just the drainage area.

Micha,

   I'm under a deadline to finish the current project, and nothing seems to
be working correctly for me.

   I just ran r.water.outlet using the drainage (aspect) map created by
r.watershed. The output is a yellow rectangle that the legend tells me
represents '0'; that is, there're no cells in the calculated basin.

   g.region -p reports:

projection: 99 (Lambert Conformal Conic)
zone:       0
datum:      nad83
ellipsoid:  grs80
north:      1334420
south:      1279150
west:       769190
east:       819260
nsres:      10
ewres:      10
rows:       5527
cols:       5007
cells:      27673689

   The command line was:

r.water.outlet drain=aber10m.drain basin=lockie e=795542.95 n=1308323.52 --o

   I can send copies of aber10m.drain and lockie. It makes no sense to me
that such a simple run fails to define the partial drainage basin. Any help
or ideas you offer will be much appreciated.

Rich