Re: [GRASS-user] Merge parallel roads
On Wed, Jun 12, 2013 at 11:21 AM, Hendrik Hoeth ho...@linta.de wrote: ... BTW, is there a way to connect the end points of two lines that are close together, but not any of the vertices along the lines? So something like v.clean tool=snap, but only for the end points? I assume that endpoints are aware of being endpoints - could this become a new tool for v.edit? Markus ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Merge parallel roads
Hi Markus, hi Hamish, thanks for your comments and ideas. I had already tried the approach v.to.rast - r.grow - r.thin - r.to.vect before, and while it kind of worked, junctions and splittings are problematic in the cleanup stage at the end, and the size of the raster map is prohibitively large (I ended up patching r.thin such that the tempfile is created on a tmpfs, in order to speed things up). I will look into your approaches during the next few days, and also give skeletron another try. BTW, is there a way to connect the end points of two lines that are close together, but not any of the vertices along the lines? So something like v.clean tool=snap, but only for the end points? Cheers, Hendrik -- If your dreams don't scare you, then you are not dreaming big enough. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Merge parallel roads
Hendrik wrote: BTW, is there a way to connect the end points of two lines that are close together, but not any of the vertices along the lines? So something like v.clean tool=snap, but only for the end points? I wonder if you could do v.to.db to extract the line-end node positions, then run v.distance with a carefully set threshold to make lines between them, then v.patch it all back together. You'd probably want to run v.build.polylines both before and after. ? Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] Merge parallel roads
Hi, I need to merge parallel roads, like highway lanes, into one. I've looked around a bit and found solutions for ArcGIS (Collapse Dual Lines To Centerline) and for OSM XML files (Skeletron), but nothing that works straight in GRASS. What's the best way of doing this in GRASS? Cheers, Hendrik -- If your dreams don't scare you, then you are not dreaming big enough. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Merge parallel roads
On Sun, Jun 9, 2013 at 10:11 AM, Hendrik Hoeth ho...@linta.de wrote: Hi, I need to merge parallel roads, like highway lanes, into one. I've looked around a bit and found solutions for ArcGIS (Collapse Dual Lines To Centerline) and for OSM XML files (Skeletron), but nothing that works straight in GRASS. What's the best way of doing this in GRASS? I have an unsubmitted module v.centerline which extracts the centerline from irregular vector polygon(s). Perhaps this approach could be used here as well. It works like this (I would be pleased to make this script available to a user who wants to make it production ready as I don't find the time): - extract vertices from polygon - triangulate (v.voronoi) - restrict to polygon of interest (v.overlay, maybe not needed for you) - TODO: here add remove-boundaries magic (with convex hull?) - skeletonize (v.net.spanningtree) - TODO: extract longest line (no idea) I think that GRASS 7 should get a generic v.centerline which does the job for both lines as well as polygons. Markus ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Merge parallel roads
Markus N wrote: I have an unsubmitted module v.centerline which extracts the centerline from irregular vector polygon(s). Perhaps this approach could be used here as well. It works like this (I would be pleased to make this script available to a user who wants to make it production ready as I don't find the time): is the prototype working well? or is it still at the theoretical/ experimental stage? I have thought about this problem a lot, it is related to the classic river mile problem which requires defining the center line of the river in a non-arbitrary way. the basic idea is to combine both parallel lines into a single map, run v.buffer to enclose them both, then get a big mosquito to pull all the volume out of the buffer until it is thinned to a single line. for two parallel lines it is not so bad, but when you get splits and convergences and islands it gets ugly. actually the raster tools are pretty good for it but they don't work well when the length:width ratio are so very different as they are for a road or a river. maintaining a similar digitization scale/vertex resolution as the original polygon is another tricky but not critically important final detail. - skeletonize (v.net.spanningtree) - TODO: extract longest line (no idea) this is an approach I have not considered. will take a little thinking about. but if v.net.spanningtree solves the worst part of the problem then I think the longest line should not be so hard to solve with one of the v.net tools. there is a bit in the archives, as well as a user donated v.centerline module, http://thread.gmane.org/gmane.comp.gis.grass.devel/36271/focus=36290 http://thread.gmane.org/gmane.comp.gis.grass.devel/36294 More on the difficulties of the river mile problem and ideas about it: http://thread.gmane.org/gmane.comp.gis.grass.user/22063/focus=22097 see also: http://article.gmane.org/gmane.comp.gis.grass.devel/11504 http://thread.gmane.org/gmane.comp.gis.grass.user/24385 http://thread.gmane.org/gmane.comp.gis.grass.user/42693/focus=42722 http://search.gmane.org/?query=river+milegroup=gmane.comp.gis.grass.user regards, Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
