[GRASS-user] Re: Defining Partial Drainage Basin

[Micha Silver]

On 02/10/2010 12:32 AM, Rich Shepard wrote:
> On Tue, 9 Feb 2010, Rich Shepard wrote:
>
>> I want to limit my analyses to that portion of the basin that drains 
>> into
>> a specified location along the main creek. Which module will allow me to
>> define a partial basin with this point as the outlet?
>
> Got it. r.water.outlet, after running r.watershed.
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, youĺl 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.
>
> BTW. is there a readily available source for learning how to interpret 
> the
> output maps of these various terrain/hydrological modules?
>
> Rich
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-- 
Micha Silver
http://www.surfaces.co.il/
Arava Development Co.  +972-52-3665918