[GRASS-user] Re: Defining Partial Drainage Basin

[Daniel Victoria]

In order for a basin to be delineated correctly, the pour point has to
be in a high accumulation area (I once heard the expression synthetic
river...)

Well, put your pour point on top of the accumulation map and see if
it's on top of the river. If not, change your easting and northing
coordinates appropriately. If you come from ArcGIS world, they have a
tool called Snap Pour Point that does that. I recall doing something
similar in grass using v.distance and a stream raster...

Good luck
Daniel

On Wed, Feb 10, 2010 at 4:22 PM, Rich Shepard <rshepard at appl-ecosys.com> wrote:
> 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
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user
>