[GRASS-user] r.watershed - Cleaning vector streams

[Markus Metz]

On Sat, Mar 30, 2019 at 5:30 PM Micha Silver <tsvibar at gmail.com> 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
>
>
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>
> --
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
>
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