Re: [GRASS-user] snap point to line/break line at given points

[Micha Silver]

On 04/24/2011 03:36 PM, Johannes Radinger wrote: Hi Micha, Hi other GRASS users! Am 23.04.2011 um 18:01 schrieb Micha Silver: 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... 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. 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). So to recap: * You can split line features at arbitrary points using v.edit tool=break * You cannot, AFAIK, cause GRASS to merge line segments where topological rules require there to be a node. Back to your problem, If you're into PostGIS, here's a post that might give you some ideas: http://postgis.refractions.net/pipermail/postgis-users/2007-September/017159.html Regards, Micha I appreciate any hints to solve that (just see the attached picture and the older posts) thanks /johannes Regards, Micha 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). This mail was received via Mail-SeCure System. Moritz _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. -- Micha Silver Arava Development Co. +972-52-3665918 http://www.surfaces.co.il <river_gen.jpg>_______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. -- Micha Silver Arava Development Co. +972-52-3665918 http://www.surfaces.co.il

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