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

[Daniel Victoria]

I think you must use the accumulation map in the r.distance command. But
bear in mind that you don't need the accumulation map but only your
drainedge lines. Thus, you can threshold the flow accum map in order to
delineate the rivers. And that could be a bit smaller than your complete
flow accumulation map.

Cheers
Daneil

On Wed, Mar 29, 2017 at 1:24 PM Ang Sherpa <angsherpa232 at gmail.com> wrote:

> Thanks Daniel,
>
> Since I am developing Grass Gis based interactive app to delineate
> watershed basin, I have to bundle those raster files along with other
> python packages. When the users installs the app, these files will be
> automatically copied and ready to use for "r.water.outlet" module through
> python script i.e. users just have to enter coordinate in the GUI.There
> will be just a single pair of coordinate at a time.
>
> My concern is that whether drainage direction raster map can be used for
> r.distance or not? Do we achieve the same result?
>
> Bundling the accumulation raster file massively increases the app setup
> file size whereas drainage direction only accounts 1/4th size of
> accumulation raster file.
>
> *Best,*
> *Ang*
>
> On Wed, Mar 29, 2017 at 9:49 PM, Daniel Victoria <
> daniel.victoria at gmail.com> wrote:
>
> 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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