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On 02/09/2012 11:59 PM, sluedtke wrote:
<blockquote cite="mid:1328824744997-4381557.post@n6.nabble.com"
type="cite">
<pre wrap="">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 class="moz-txt-link-freetext" 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 cite="mid:1328824744997-4381557.post@n6.nabble.com"
type="cite">
<pre wrap="">
Thanks in advance,
Stefan
--
View this message in context: <a class="moz-txt-link-freetext" href="http://osgeo-org.1560.n6.nabble.com/How-to-link-or-combine-adjacent-vector-lines-tp4381557p4381557.html">http://osgeo-org.1560.n6.nabble.com/How-to-link-or-combine-adjacent-vector-lines-tp4381557p4381557.html</a>
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</pre>
</blockquote>
<p><br>
</p>
<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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