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

GRASS GRASS user
1

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

2

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@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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3

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.

···

On Wed, Mar 29, 2017 at 9:49 PM, Daniel Victoria <daniel.victoria@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@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

grass-user mailing list
grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

Best,
Ang

4

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

···

Best,
Ang

On Wed, Mar 29, 2017 at 9:49 PM, Daniel Victoria <daniel.victoria@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@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

grass-user mailing list
grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

5

Ang Sherpa 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?

what about?:

https://grass.osgeo.org/grass72/manuals/addons/r.stream.snap.html

r.stream.snap - Snap point to modelled stream network.
Input can be stream network, point vector map with outlets or outlet
coordinates.

-----
best regards
Helmut
--
View this message in context: http://osgeo-org.1560.x6.nabble.com/snap-pour-point-for-r-water-outlet-tp5314835p5314856.html
Sent from the Grass - Users mailing list archive at Nabble.com.

6

Thanks for the link Helmut,

However, it throws an error stating:

(Thu Mar 30 09:14:55 2017)
r.stream.snap
‘r.stream.snap’ is not recognized as an internal or external
command,
operable program or batch file.

I am using standalone version Grass gis 7.2.0

···

On Thu, Mar 30, 2017 at 1:03 AM, Helmut Kudrnovsky <hellik@web.de> wrote:

Ang Sherpa 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?

what about?:

https://grass.osgeo.org/grass72/manuals/addons/r.stream.snap.html

r.stream.snap - Snap point to modelled stream network.
Input can be stream network, point vector map with outlets or outlet
coordinates.

best regards
Helmut

View this message in context: http://osgeo-org.1560.x6.nabble.com/snap-pour-point-for-r-water-outlet-tp5314835p5314856.html
Sent from the Grass - Users mailing list archive at Nabble.com.

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Regards,
Ang Dawa Sherpa
GIS technician - Irrigation Master Plan
WRPPF - DOI, Nepal Government
Lalitpur
contact: 984 007 3861