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On 02/11/2012 08:49 PM, Stefan Luedtke wrote:
<blockquote cite="mid:1328986155.2407.17.camel@hydro44" type="cite">
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Sorry for the delay... and thanks for the fast answer. <br>
<br>
Adding a column and then running a command in the sense of
"v.dissolve" is not an option because there are just to many. I
was thinking of a way that combines <b><u>two</u></b> lines into
one if they share the same node. For the example mentioned the
last time, this means, keeping the line as a single one until the
tributary merges the main river. The main river might consist of
more than one line, but a short tributary should not. <br>
<br>
</blockquote>
<br>
How will you (or the command) know which lines to combine?<br>
<br>
There is: v.edit tool=merge or v.edit tool=connect<br>
But AFAIK these will not allow you to break topology.<br>
<br>
<br>
<blockquote cite="mid:1328986155.2407.17.camel@hydro44" type="cite">
I hope I dont miss anything obvious .... ;-)<br>
<br>
Cheers, <br>
<br>
Stefan<br>
<br>
On Fri, 2012-02-10 at 17:04 +0200, Micha Silver wrote:<br>
<blockquote type="CITE"> On 02/09/2012 11:59 PM, sluedtke wrote:
<blockquote type="CITE">
<pre>Dear friends,
I have been trying for some hours now but could not find any solution.
We do have a shape file of a river network, but a bad one because single
rivers consist of multiple lines. Just think of the easiest example, a river
with one tributary. I would like to end up with an vector dataset that holds
2 lines for this example, one for the river and one for the tributary of
course. In my case, the dataset holds, just as an example, 10 lines, and a
distinct set of them makes either the river or the tributary. The lines of
each set are connected by the nodes of the single lines.
Any ideas how to get ride of this format are very welcome.
</pre>
</blockquote>
<br>
You might be interested in this thread from a year ago.<br>
<a moz-do-not-send="true"
href="http://osgeo-org.1560.n6.nabble.com/snap-point-to-line-break-line-at-given-points-tp3887413p3887413.html">http://osgeo-org.1560.n6.nabble.com/snap-point-to-line-break-line-at-given-points-tp3887413p3887413.html</a><br>
<br>
The short story is that GRASS builds topology when importing a
line vector. So each intersection of two lines (i.e. a tributary
that branches off the main channel) will be made into a separate
line. You can force GRASS to ignore topology, but you probably
don't want to. And a correct river network does indeed keep
each stream reach as a separate line. (Then you can use the
various river network modules r.stream.*). So maybe your
original shapefile is not "bad"...<br>
<br>
What you can do it add an additional column to the vector attrib
table and indicate, in that column, which tributary each segment
belongs to. THen you can select, display, label, calculate, etc
based on this "tributary" attribute column. Would that help?<br>
<br>
<br>
<blockquote type="CITE">
<pre>Thanks in advance,
Stefan
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</pre>
</blockquote>
<br>
<br>
<br>
<pre>--
Micha Silver
GIS Consultant, Arava Development Co.
<a moz-do-not-send="true" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a>
</pre>
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<br>
<pre class="moz-signature" cols="72">--
Micha Silver
GIS Consultant, Arava Development Co.
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a></pre>
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