On Sat, Oct 28, 2017 at 3:18 PM, Huidae Cho <gras...@gmail.com> wrote: > > BTW, let me understand weakly vs strongly connected components generated by v.net.components. > > Strongly connected: All paths between nodes u and v should have the same direction.
>From the manual: "there are directed paths from u to v and from v to u" You can create directed graphs by assigning costs according to line direction with the arc_column and arc_backward_column options. The forward or backward direction of a line can be closed by setting costs to -1. By default, (no cost columns given), line lengths are used as costs, ignoring line direction because 1) line direction can be arbitrary, 2) typically lines can be traversed in both directions. Therefore, method=strong only makes sense if both arc_column and arc_backward_column are given and if some lines are closed in one direction. Otherwise, strong and weak will give the same results. > > Weakly connected: Only requires "connections" between nodes u and v, and their directions don't matter. To be precise, u must be reachable from v or v must be reachable from u. > > If my understanding is correct, a stream vector map generated by thinning and converting the stream raster map (flow directions not guaranteed) to vector would only be weakly connected. > > The stream vector output from r.streams.extract would be both strongly and weakly connected because it honors flow directions. Different stream networks are always different components. If you use arc_backward_column and close backward traversal, each stream network is again broken up into various strongly connected components. If you use r.thin + r.to.vect + arc_backward_column, a single stream network might even be broken up into several weakly connected components. HTH, Markus M > > Please let me know if I'm mistaken. > > Thanks. > Huidae > > > > On Sat, Oct 28, 2017 at 9:06 AM, Huidae Cho <gras...@gmail.com> wrote: >> >> It's working great! Thanks for the quick implementation. It will help a lot! >> >> Huidae >> >> On Fri, Oct 27, 2017 at 3:58 PM, Markus Metz < markus.metz.gisw...@gmail.com> wrote: >>> >>> >>> >>> On Fri, Oct 27, 2017 at 2:38 PM, Huidae Cho <gras...@gmail.com> wrote: >>> > >>> > [...] I tried your r.stream.extract to extract stream lines and its output makes much more sense. It would be great if this module also outputs unique stream "network" numbers. >>> >>> Unique stream network numbers are added as new attribute "network" in trunk r71599. >>> >>> Markus M >>> > >>> > Thanks. >>> > Huidae >>> > >>> > >>> > On Fri, Oct 27, 2017 at 8:14 AM, Markus Metz < markus.metz.gisw...@gmail.com> wrote: >>> >> >>> >> >>> >> >>> >> On Fri, Oct 27, 2017 at 12:52 PM, Huidae Cho <gras...@gmail.com> wrote: >>> >> > >>> >> > Actually, I'm getting the same error as Markus in the NC dataset. I recently discleaned and rebuilt the latest SVN. >>> >> >>> >> In trunk, this bug appeared with r71267 and was fixed with r71477. >>> >> In relbr72, this bug appeared with r71268 and was fixed with r71478. >>> >> >>> >> Please check your revision. >>> >> >>> >> Markus M >>> >> >>> >> > >>> >> > Huidae >>> >> > >>> >> > On Thu, Oct 26, 2017 at 4:14 PM, Markus Metz < markus.metz.gisw...@gmail.com> wrote: >>> >> >> >>> >> >> >>> >> >> >>> >> >> On Thu, Oct 26, 2017 at 5:02 PM, Markus Neteler <nete...@osgeo.org> wrote: >>> >> >> > >>> >> >> > On Thu, Oct 26, 2017 at 9:58 AM, Stefan Blumentrath >>> >> >> > <stefan.blumentr...@nina.no> wrote: >>> >> >> > > Hi, >>> >> >> > > >>> >> >> > > Did you try: >>> >> >> > > >>> >> >> > > https://grass.osgeo.org/grass72/manuals/v.net.components.html >>> >> >> > > >>> >> >> > > That might give you a common attribute for all connected lines in your >>> >> >> > > network… >>> >> >> > >>> >> >> > I just tried that with NC but: >>> >> >> > >>> >> >> > GRASS 7.3.svn (nc_spm_08_grass7):~ > v.net.components input=roadsmajor >>> >> >> > output=roadsmajor_components method=strong >>> >> >> > Building graph... >>> >> >> > Registering arcs... >>> >> >> > 100% >>> >> >> > Flattening the graph... >>> >> >> > ERROR: GngFlatten error >>> >> >> > >>> >> >> > >>> >> >> > GRASS 7.3.svn (nc_spm_08_grass7):~ > v.net.components input=railroads >>> >> >> > output=railroads_components method=strong >>> >> >> > Building graph... >>> >> >> > Registering arcs... >>> >> >> > 100% >>> >> >> > Flattening the graph... >>> >> >> > ERROR: GngFlatten error >>> >> >> > >>> >> >> > Does the network need any special treatment? >>> >> >> >>> >> >> I can not reproduce these errors. Please update your local copy: >>> >> >> make distclean >>> >> >> svn --no-ignore status >>> >> >> svn up >>> >> >> configure >>> >> >> make >>> >> >> >>> >> >> Markus M >>> >> >> > >>> >> >> > Markus >>> >> >> > _______________________________________________ >>> >> >> > grass-user mailing list >>> >> >> > grass-user@lists.osgeo.org >>> >> >> > https://lists.osgeo.org/mailman/listinfo/grass-user >>> >> >> >>> >> >> >>> >> >> _______________________________________________ >>> >> >> grass-user mailing list >>> >> >> grass-user@lists.osgeo.org >>> >> >> https://lists.osgeo.org/mailman/listinfo/grass-user >>> >> > >>> >> > >>> > >>> > >> >> >
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