[GRASS-user] How to link or combine adjacent vector lines

[Stefan Luedtke]

On Sat, 2012-02-11 at 21:26 +0200, Micha Silver wrote:

> On 02/11/2012 08:49 PM, Stefan Luedtke wrote: 
> 
> > Sorry for the delay... and thanks for the fast answer. 
> > 
> > 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 two 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. 
> > 
> 
> 
> How will you (or the command) know which lines to combine?


That a difficult question, indeed. Maybe there is no way and I have to
do it manually.
Anyway- thanks for you comments. 

Take care.

> 
> There is: v.edit tool=merge or v.edit tool=connect
> But AFAIK these will not allow you to break topology.
> 
> 
> 
> > I hope I dont miss anything obvious .... ;-)
> > 
> > Cheers, 
> > 
> > Stefan
> > 
> > On Fri, 2012-02-10 at 17:04 +0200, Micha Silver wrote:
> > 
> > > On 02/09/2012 11:59 PM, sluedtke wrote: 
> > > 
> > > > 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. 
> > > 
> > > 
> > > You might be interested in this thread from a year ago.
> > > http://osgeo-org.1560.n6.nabble.com/snap-point-to-line-break-line-at-given-points-tp3887413p3887413.html
> > > 
> > > 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"...
> > > 
> > > 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?
> > > 
> > > 
> > > 
> > > > Thanks in advance, 
> > > > 
> > > > Stefan
> > > > 
> > > > 
> > > > 
> > > > --
> > > > View this message in context: http://osgeo-org.1560.n6.nabble.com/How-to-link-or-combine-adjacent-vector-lines-tp4381557p4381557.html
> > > > Sent from the Grass - Users mailing list archive at Nabble.com.
> > > > _______________________________________________
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> > > > grass-user at lists.osgeo.org
> > > > http://lists.osgeo.org/mailman/listinfo/grass-user
> > > > 
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> > > > 
> > > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > -- 
> > > Micha Silver
> > > GIS Consultant, Arava Development Co.
> > > http://www.surfaces.co.il
> > 
> > 
> > 
> > This mail was received via Mail-SeCure System.
> 
> 
> 
> 
> 
> -- 
> Micha Silver
> GIS Consultant, Arava Development Co.
> http://www.surfaces.co.il
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