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Hi Johannes:<br>
<br>
On 04/22/2011 05:15 PM, Johannes Radinger wrote:
<blockquote cite="mid:A1079EC0-399F-4329-B497-BEC0DD30F786@gmx.at"
type="cite">
<pre wrap="">
Am 22.04.2011 um 13:22 schrieb Moritz Lennert:
</pre>
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<pre wrap="">On 22/04/11 11:34, Johannes Radinger wrote:
</pre>
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<pre wrap="">About my situation: I've got a river network, which
is a polylinefeature set with 43 lines (43 IDs) included (tree-like shape of a rivernet)
all with the same cat-value (1).
Now I would like to unite/merge the lines to one feature (1 ID) if that is possible
and break that single element at given points with v.edit...Because if I break
now at around 40 positions I get over 80 segements (40 old segements and which
are broken again at different positions) but there should be only
41 or so...
so how can I handle that and assign unique cat values for each segment...(at the
moment the don't have to be the same like the breakpoints, just unique values)
any suggestions?
</pre>
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<pre wrap="">
v.edit tool=catadd id= ?
</pre>
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<pre wrap="">
Sorry but I am still confused how to do the break.
In the Attachment there is a GRASS-exported shp.-file with my
rivernet consisting of 43 single lines.
I want to break that river at e.g. 3521021.43671,6041340.79067
which is one point (out of others) along the river.
</pre>
</blockquote>
<br>
Here's what I tried:<br>
<br>
GRASS 6.4.0 (WGS84):~/geodata > v.edit river_gen tool=break
coords="3521021.43671,6041340.79067"<br>
Selecting features...<br>
100%<br>
1 of 43 features selected from vector map
<river_gen@PERMANENT><br>
100%<br>
1 lines broken<br>
Building topology for vector map <river_gen>...<br>
Registering primitives...<br>
44 primitives registered<br>
17135 vertices registered<br>
Building areas...<br>
100%<br>
0 areas built<br>
0 isles built<br>
Attaching islands...<br>
Attaching centroids...<br>
100%<br>
Number of nodes: 45<br>
Number of primitives: 44<br>
Number of points: 0<br>
Number of lines: 44<br>
Number of boundaries: 0<br>
Number of centroids: 0<br>
Number of areas: 0<br>
Number of isles: 0<br>
v.edit complete.<br>
<br>
So I there are now 44 line segments as opposed to the original 43.
One got split into two. But the two new segments have the same cat
number.<br>
Next I wiped out all the old cats:<br>
GRASS 6.4.0 (WGS84):~/geodata > v.category river_gen opt=del
cat=1-43 out=river_gen_tmp<br>
and recreated new cats into a new vector:<br>
GRASS 6.4.0 (WGS84):~/geodata > v.category --o river_gen_tmp
opt=add out=river_gen_2<br>
<br>
In the attached image you can see that the original line segment
with cat=12 (black numbers) got split into two (after the v.edit
step). THe red numbers are the new cat values, and that line segment
got cats 43 and 44.<br>
<br>
Reviewing your first post I want to also note:<br>
I believe that GRASS's topology model will not allow you to merge
the original river segments into one "polyline" (MULTILINE in other
GIS). You *can* of course have polylines in GRASS, but they must
consist of two line segments connected at exactly one point. In any
typical river network you always have three segments intersecting:
the upstream reach, the tributary and the downstream reach. <br>
Others with more experience may correct me, but I think that if you
must merge all the river segments into one "MULTILINE" before
splitting at the new points, then you'll have to use some other tool
and non-topological vector data format outside of GRASS. <br>
<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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Moritz
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</blockquote>
<br>
<br>
<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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