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List: grass-user
Subject: Re: [GRASS-user] r.watershed - Cleaning vector streams
From: Adrien_André <adr.andre () laposte ! net>
Date: 2019-03-31 20:20:00
Message-ID: 45166bf3-ffeb-74f4-d9d8-431f9f732027 () laposte ! net
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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 <tsvibar@gmail.com
> <mailto:tsvibar@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
> >
> >
> > _______________________________________________
> > grass-user mailing list
> > grass-user@lists.osgeo.org <mailto:grass-user@lists.osgeo.org>
> > 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
> > grass-user@lists.osgeo.org <mailto:grass-user@lists.osgeo.org>
> > https://lists.osgeo.org/mailman/listinfo/grass-user
--
Adrien
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<p>Thank you for your help,</p>
<p>i'll try r.stream.extract</p>
<p>I do have set a small threshold value but it is on purpose.<br>
The streams i am trying to model are not hydrological.</p>
<p>Best regards,</p>
<p>Adrien<br>
</p>
<div class="moz-cite-prefix">Le 19-03-31 Ã 09 h 48, Markus Metz a
écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CAG+h=FHVqqeouDQEH8eaSh1dSo6GP11MVNBsgHejen3YhfTV+A@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr"><br>
<br>
On Sat, Mar 30, 2019 at 5:30 PM Micha Silver <<a
href="mailto:tsvibar@gmail.com" \
moz-do-not-send="true">tsvibar@gmail.com</a>> wrote:<br>
><br>
><br>
> On 29/03/2019 22:03, Adrien André wrote:<br>
><br>
> Hello,<br>
><br>
> following the wiki doc about stream extraction [1], once
the stream layer thinned and vectorized,<br>
> there are many small arcs i would like to remove (see
attached capture [2]).<br>
><br>
> So, with the underlying drainage direction map [3], and the
resolution r, i would like to delete segments<br>
> - about r*sqrt(2) long<br>
> - whose azimuth is more than 45 ° different from the pixel
value under its starting point.<br>
><br>
><br>
> This might be possible, but I think the best approach would
be to choose the correct threshold value for r.watershed from
the start.<br>
><br>
> Trying to manually "fiddle" with the stream network will
most likely leave you with disconnected segments, or other
inconsistencies.<br>
<div><br>
</div>
<div>+1</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>Markus M</div>
<div><br>
</div>
<div>></div>
><br>
> But i still haven't figured a way to achieve this.<br>
><br>
> Do you have any advice ?<br>
><br>
> Thank you,<br>
><br>
> Best regards,<br>
><br>
> [1] <a
href="https://grasswiki.osgeo.org/wiki/Creating_watersheds#Display_first_results"
moz-do-not-send="true">https://grasswiki.osgeo.org/wiki/Creating_watersheds#Display_first_results</a><br>
> [2] <a
href="https://framapic.org/1exdxrdqxemw/ytuVxiBp2FKh.png"
moz-do-not-send="true">https://framapic.org/1exdxrdqxemw/ytuVxiBp2FKh.png</a><br>
> [3] <a
href="https://grass.osgeo.org/grass74/manuals/r.watershed.html"
moz-do-not-send="true">https://grass.osgeo.org/grass74/manuals/r.watershed.html</a><br>
><br>
><br>
> _______________________________________________<br>
> grass-user mailing list<br>
> <a href="mailto:grass-user@lists.osgeo.org"
moz-do-not-send="true">grass-user@lists.osgeo.org</a><br>
> <a
href="https://lists.osgeo.org/mailman/listinfo/grass-user"
moz-do-not-send="true">https://lists.osgeo.org/mailman/listinfo/grass-user</a><br>
><br>
> -- <br>
> Micha Silver<br>
> Ben Gurion Univ.<br>
> Sde Boker, Remote Sensing Lab<br>
> cell: +972-523-665918<br>
><br>
> _______________________________________________<br>
> grass-user mailing list<br>
> <a href="mailto:grass-user@lists.osgeo.org"
moz-do-not-send="true">grass-user@lists.osgeo.org</a><br>
> <a
href="https://lists.osgeo.org/mailman/listinfo/grass-user"
moz-do-not-send="true">https://lists.osgeo.org/mailman/listinfo/grass-user</a></div>
</blockquote>
<pre class="moz-signature" cols="72">--
Adrien</pre>
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