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On 04/24/2011 03:36 PM, Johannes Radinger wrote:
<blockquote cite="mid:1B8FCF4F-AAE3-40BB-B1AA-635AF2E27C6F@gmx.at"
type="cite">Hi Micha,
<div>Hi other GRASS users!</div>
<div><br>
<div>
<div>Am 23.04.2011 um 18:01 schrieb Micha Silver:</div>
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<div>So if I understand you correctly, it is not really
possible to split a river network at one point into to
parts. I attached a picture to illustrate what I want
(e.g. two break points in a rivernet). I think that this
kind of breaking I want to do is quite common, so there's
probably another solution in grass gis...</div>
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</blockquote>
<br>
Well, in QGIS you can merge all the line segments of the original
shapefile into one, using the "Vector->Geometry
Tools->Singleparts to Multipart" tool. This will leave you with a
single "MULTILINE" feature. <br>
<br>
However when importing to GRASS all the lines will be "re-broken" at
each intersection and new nodes created in order to enforce
topology. Referring to the attached image (I altered yours) the
stars represent topological "errors" and as far as I know GRASS will
not allow you to ignore these intersections when you import. (The
only vector feature that can be imported without topology is
points).<br>
<br>
So to recap:<br>
* You can split line features at arbitrary points using v.edit
tool=break<br>
* You cannot, AFAIK, cause GRASS to merge line segments where
topological rules require there to be a node.<br>
<br>
Back to your problem, If you're into PostGIS, here's a post that
might give you some ideas:<br>
<a
href="http://postgis.refractions.net/pipermail/postgis-users/2007-September/017159.html">http://postgis.refractions.net/pipermail/postgis-users/2007-September/017159.html</a><br>
<br>
Regards,<br>
Micha<br>
<br>
<br>
<blockquote cite="mid:1B8FCF4F-AAE3-40BB-B1AA-635AF2E27C6F@gmx.at"
type="cite">
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<div><br>
</div>
<div>I appreciate any hints to solve that (just see the
attached picture and the older posts)</div>
<div><br>
</div>
<div>thanks</div>
<div>/johannes</div>
</div>
<div><br>
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<br>
<blockquote type="cite">
<div bidimailui-charset-is-forced="true"
bidimailui-detected-decoding-type="preferred-charset"
text="#000000" bgcolor="#ffffff"> <br>
Regards,<br>
Micha<br>
<br>
<br>
<blockquote
cite="mid:A1079EC0-399F-4329-B497-BEC0DD30F786@gmx.at"
type="cite">
<pre wrap="">In the end I want two features/categories one on each side of the break.
what are the exact steps especially when I want to do it with several points
(I know the procedure with a python for loop in combination with v.edit).
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<blockquote type="cite">
<pre wrap="">Moritz
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<br>
<pre class="moz-signature" cols="72">--
Micha Silver
Arava Development Co. +972-52-3665918
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://www.surfaces.co.il/">http://www.surfaces.co.il</a>
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<pre class="moz-signature" cols="72">--
Micha Silver
Arava Development Co. +972-52-3665918
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a>
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