r.watershed - Cleaning vector streams

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r.watershed - Cleaning vector streams

Adrien ANDRÉ
Hello,

following the wiki doc about stream extraction [1], once the stream
layer thinned and vectorized,
there are many small arcs i would like to remove (see attached capture [2]).

So, with the underlying drainage direction map [3], and the resolution
r, i would like to delete segments
- about r*sqrt(2) long
- whose azimuth is more than 45° different from the pixel value under
its starting point.

But i still haven't figured a way to achieve this.

Do you have any advice ?

Thank you,

Best regards,

[1]
https://grasswiki.osgeo.org/wiki/Creating_watersheds#Display_first_results
[2] https://framapic.org/1exdxrdqxemw/ytuVxiBp2FKh.png
[3] https://grass.osgeo.org/grass74/manuals/r.watershed.html

--
Adrien


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Re: r.watershed - Cleaning vector streams

Micha Silver-2

On 29/03/2019 22:03, Adrien André wrote:
Hello,

following the wiki doc about stream extraction [1], once the stream layer thinned and vectorized,
there are many small arcs i would like to remove (see attached capture [2]).

So, with the underlying drainage direction map [3], and the resolution r, i would like to delete segments
- about r*sqrt(2) long
- whose azimuth is more than 45° different from the pixel value under its starting point.


This might be possible, but I think the best approach would be to choose the correct threshold value for r.watershed from the start.

Trying to manually "fiddle" with the stream network will most likely leave you with disconnected segments, or other inconsistencies.


But i still haven't figured a way to achieve this.

Do you have any advice ?

Thank you,

Best regards,

[1] https://grasswiki.osgeo.org/wiki/Creating_watersheds#Display_first_results
[2] https://framapic.org/1exdxrdqxemw/ytuVxiBp2FKh.png
[3] https://grass.osgeo.org/grass74/manuals/r.watershed.html


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Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918

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Re: r.watershed - Cleaning vector streams

Markus Metz-3


On Sat, Mar 30, 2019 at 5:30 PM Micha Silver <[hidden email]> wrote:

>
>
> On 29/03/2019 22:03, Adrien André wrote:
>
> Hello,
>
> following the wiki doc about stream extraction [1], once the stream layer thinned and vectorized,
> there are many small arcs i would like to remove (see attached capture [2]).
>
> So, with the underlying drainage direction map [3], and the resolution r, i would like to delete segments
> - about r*sqrt(2) long
> - whose azimuth is more than 45° different from the pixel value under its starting point.
>
>
> This might be possible, but I think the best approach would be to choose the correct threshold value for r.watershed from the start.
>
> Trying to manually "fiddle" with the stream network will most likely leave you with disconnected segments, or other inconsistencies.

+1

Please try r.stream.extract in order to get a clean vector stream network. The approach r.thin + r.to.vect creates noise and does not always follow flow directions.

Markus M

>
>

> But i still haven't figured a way to achieve this.
>
> Do you have any advice ?
>
> Thank you,
>
> Best regards,
>
> [1] https://grasswiki.osgeo.org/wiki/Creating_watersheds#Display_first_results
> [2] https://framapic.org/1exdxrdqxemw/ytuVxiBp2FKh.png
> [3] https://grass.osgeo.org/grass74/manuals/r.watershed.html
>
>
> _______________________________________________
> grass-user mailing list
> [hidden email]
> https://lists.osgeo.org/mailman/listinfo/grass-user
>
> --
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
>
> _______________________________________________
> grass-user mailing list
> [hidden email]
> https://lists.osgeo.org/mailman/listinfo/grass-user
_______________________________________________
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[hidden email]
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Re: r.watershed - Cleaning vector streams

Adrien ANDRÉ

Thank you for your help,

i'll try r.stream.extract

I do have set a small threshold value but it is on purpose.
The streams i am trying to model are not hydrological.

Best regards,

Adrien

Le 19-03-31 à 09 h 48, Markus Metz a écrit :


On Sat, Mar 30, 2019 at 5:30 PM Micha Silver <[hidden email]> wrote:
>
>
> On 29/03/2019 22:03, Adrien André wrote:
>
> Hello,
>
> following the wiki doc about stream extraction [1], once the stream layer thinned and vectorized,
> there are many small arcs i would like to remove (see attached capture [2]).
>
> So, with the underlying drainage direction map [3], and the resolution r, i would like to delete segments
> - about r*sqrt(2) long
> - whose azimuth is more than 45° different from the pixel value under its starting point.
>
>
> This might be possible, but I think the best approach would be to choose the correct threshold value for r.watershed from the start.
>
> Trying to manually "fiddle" with the stream network will most likely leave you with disconnected segments, or other inconsistencies.

+1

Please try r.stream.extract in order to get a clean vector stream network. The approach r.thin + r.to.vect creates noise and does not always follow flow directions.

Markus M

>
>
> But i still haven't figured a way to achieve this.
>
> Do you have any advice ?
>
> Thank you,
>
> Best regards,
>
> [1] https://grasswiki.osgeo.org/wiki/Creating_watersheds#Display_first_results
> [2] https://framapic.org/1exdxrdqxemw/ytuVxiBp2FKh.png
> [3] https://grass.osgeo.org/grass74/manuals/r.watershed.html
>
>
> _______________________________________________
> grass-user mailing list
> [hidden email]
> https://lists.osgeo.org/mailman/listinfo/grass-user
>
> --
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
>
> _______________________________________________
> grass-user mailing list
> [hidden email]
> https://lists.osgeo.org/mailman/listinfo/grass-user
-- 
Adrien

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