[GRASS-user] [snap pour point for r.water.outlet]

[Daniel Victoria]

Hi Ang,

I had replied off list. I'm now replying to the list so other can comment

The idea is that to delineate watersheds, the outlet has to lie in a place
with high accumulation. So if you get your outlet points a bit messed up, a
way to force them to go to the right place is to use r.distance.

I don't have a specific code nor I recall the steps I've taken back in
2010, when I did this. But, looking at the r.distance manual [1], this is
what I'd try if I had to repeat the process today:

1) Convert my outlet points to raster, each with a different category
2) Threshold your flow accumulation map in order to delineate the rivers
(high flow accumulation)
3) Run r.distance to find the closest river line to each of your output
point. Check that you don't create any points to far away from the original
position.
4) Use the output of r.distance as the coordinates in r.water.outlet

Cheers
Daniel

[1] - https://grass.osgeo.org/grass72/manuals/r.distance.html

On Wed, Mar 29, 2017 at 12:55 PM Ang Sherpa <angsherpa232 at gmail.com> wrote:

> Hi users,
>
> While using "r.water.outlet" to delineate watershed basin, although the
> coordinates of the stream was noted from google earth and fed into
> "r.water.outlet" module, it produces plain raster.
>
> Is there any solution to make sure that the coordinates of outlet point
> automatically snaps to the nearest line of stream in drainage direction map?
>
>
> Any words will be appreciated.
>
>
> *Best,*
> *Ang*
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