Thank you Markus, indeed your approach looks like what I need..The hint with v.net.components was the part that I was missing; I'll try as soon as possible and will report back on how this works. cheers, Johannes
On Wed, Mar 11, 2020 at 10:16 PM Markus Metz <markus.metz.gisw...@gmail.com> wrote: > Hi Johannes, > > IIUC, what you want to do is an operation that involves topological > relations of vector geometries (connected lines) and a common attribute. > There is no easy common recipe for this. > > Just a suggestion: > for each stream order: > extract all lines with this stream order (v.extract) > identify connected lines (v.net + v.net.components) > update a new attribute of the original lines with the comp attribute of > the output of v.net.components plus some offset to separate different > stream orders > > HTH, > > Markus M > > > On Tue, Mar 10, 2020 at 5:20 PM Johannes Radinger < > johannesradin...@gmail.com> wrote: > > > > So...no also with GRASS-user as recipient... > > > > On 05.03.20 16:21, Micha Silver wrote: > > > > > > On 3/5/20 10:47 AM, Johannes Radinger wrote: > > >> > > >> Hi Micha, hi all, > > >> > > >> sorry for my late response...however, just today I managed to try > > >> your approach of building polylines to connect "touching stream > > >> lines"...but... > > >> > > >> On 24.02.20 16:48, Micha Silver wrote: > > >>> > > >>> On 24/02/2020 10:45, Johannes Radinger wrote: > > >>>> Hi all, > > >>>> I have a large river network dataset (lines). Now I'd to assign > > >>>> unique categories to each group of connected lines that have an > > >>>> attribute in common. > > >>>> > > >>>> For example, my rivers are categorized based on some kind of stream > > >>>> order. I want to group all rivers that belong to stream order 2 and > > >>>> are spatially connected; each group should get a unique category > > >>>> value. I thought that I could first extract all rivers with a > > >>>> particular attribute (e.g. stream order = 2) which will provide me > > >>>> some scattered pattern of lines. Then I need a spatial join tool to > > >>>> make subgroups of lines that are connected. How can I achieve the > > >>>> latter? Any idea? > > >>> > > > > > > > > >>> > > >>> Here's a procedure that might work for you. Somewhat clunky, but I > > >>> think it gets what you want. > > >>> > > >>> It's based on the v.build.polylines module to connect all touching > > >>> stream reaches. First extract each order from the stream vector into > > >>> a new vector. Then build polylines. Patch them all together. Now you > > >>> have a polyline vector with a single cat value for each set of > > >>> original stream reaches that had the same order and that were > touching. > > >> > > >> Unfortunately, the v.build.polylines tool does not work as it only > > >> does not connect multiple (intersecting) lines like in a river > > >> network. As an example I tried to build polylines from the stream > > >> network of the NC dataset. Yous suggested approach should result that > > >> each sub-network (i.e. river network that is not connected to another > > >> one) should get its own ID/cat...however, v.build.polylines results > > >> in a connected stream network that consists of multiple cats: > > >> > > > Maybe I misunderstood your question. The steps I tried use a > > > stream_order column to group stream segments, then apply a new > > > attribute "merged_id" to those stream orders that touch. i.e. that > > > connect to the same confluence point. > > > > > > > > > Here's what I get using the nc_basic_spm mapset: > > > > > > > > > r.watershed elev=elevation accum=nc_facc drain=nc_fdir bas=nc_bas > > > stream=nc_str thresh=1000 > > > r.stream.order stream_rast=nc_str direct=nc_fdir elev=elevation > > > accum=nc_facc stream_vect=nc_streams > > > ORDERS=`v.db.select -c nc_streams group=strahler column=strahler` > > > echo $ORDERS > > > > > > # Create a new stream vector for each stream order > > > > > > for o in $ORDERS; do > > > > > > v.extract input=nc_streams output=streams_${o} > where="strahler=${o}" > > > > > > # Give each polyline it's own cat value > > > > > > v.build.polylines input=streams_${o} output=streams_${o}_polyline > > > type=line cat=first > > > > > > done > > > > > > > > > # patch the stream orders back together > > > > > > POLYLINES=`g.list vect pattern="streams*polyline" separator=comma` > > > > > > v.patch input=$POLYLINES output=streams_polylines > > > > > > v.db.addcolumn map=streams column="merged_id INTEGER" > > > > > > > > > # And use v.distance to update that merged_id column from cat values > > > in polylines vector > > > v.distance from=streams to=streams_polylines upload=cat > column=merged_id > > > v.db.addcolumn map=nc_streams column="merged_id INTEGER" > > > v.distance from=nc_streams to=streams_polylines upload=cat > > > column=merged_id > > > > > > Now, all stream reaches that have the same order and are "touching" > > > have the same merged_id. See the attached image. > > > > > > > > > If that's not your purpose, then just ignore... > > > > > Micha thank you for your help and of course, you're fully correct! > > Merging lines that belong to the same stream order works in this case > > well...but this is because of the definition of the Strahler ordering > > system, where there is only one "touching node" (i.e. river junction) of > > two rivers of the same stream order (i.e. when two 2nd order streams > > meet, the become a 3rd order stream). Thus your solution works because > > of this specifics and might not work if streams are grouped based on a > > different (ordering) system. > > > > I was already thinking of the next step (beyond simple Strahler): As > > mentioned in my initial post I am dealing with "some kind" of stream > > order. It is similar to grouped stream orders (e.g. stream order 1-2 = > > "headwater streams"). I tried to somehow reproduce my situation based on > > your example of the NC dataset. What I basically did was to reassign a > > new stream order "99" to all former 1st and 2nd order streams. Then I > > did exactly what you did in your example, and of course I don't unique > > merged_ids for the subnetworks of touching lines (see attached Figs) > > that all belong the the same "order" 99 (the original strahler order 3 > > works of course, see Fig.)...So is there a more general way (as said > > something like v.dissolve but for lines/networks?): > > > > ##################### > > g.region raster=elevation > > > > r.watershed --o elev=elevation accum=nc_facc drain=nc_fdir bas=nc_bas > > stream=nc_str thresh=1000 > > r.stream.order stream_rast=nc_str direct=nc_fdir elev=elevation > > accum=nc_facc stream_vect=nc_streams > > > > #ORDERS=`v.db.select -c nc_streams group=strahler column=strahler` > > #echo $ORDERS > > > > # Regroup orders 1-2 (to 99) > > v.db.addcolumn map=nc_streams@test2 columns="strahler_groups INTEGER" > > v.db.update map=nc_streams column=strahler_groups query_column=strahler > > v.db.update map=nc_streams column=strahler_groups value=99 > > where="strahler=1 OR strahler=2" > > > > NEWORDERS=`v.db.select -c nc_streams group=strahler_groups > > column=strahler_groups` > > echo $NEWORDERS > > > > # Create a new stream vector for each stream order > > for o in $NEWORDERS; do > > v.extract input=nc_streams output=streams_${o} > > where="strahler_groups=${o}" > > # Give each polyline it's own cat value > > v.build.polylines input=streams_${o} output=streams_${o}_polyline > > type=line cat=first > > done > > > > d.vect -c map=streams_99_polyline@test2 > > ################# > > > > Thank you very much! > > > > Cheers, > > > > Johannes > > > > > > > >> v.clean --overwrite input=streams@PERMANENT output=streams_break > > >> tool=break > > >> v.build.polylines --overwrite input=streams_break@test > > >> output=streams_poly cats=first type=line > > >> d.vect -c map=streams_poly > > >> > > >> So what would be needed here is some kind of tool that connects all > > >> touching lines and assigns a common category value, similar to the > > >> v.dissolve tool for polygon features. I can imagine that such a task > > >> might be not that uncommon also in another context? Any suggestions > > >> how to achieve this in GRASS? > > >> > > >> A workaround that came into my mind was to create buffers around > > >> lines in order to make areas out of lines. Subsequently these > > >> touching areas can be merged using v.dissolve and the information > > >> about the common category can be queried using v.distance. > > >> Nevertheless, a rather cumbersome way to just assign a common > > >> category value to all lines that are touching... > > >> > > >> Any further ideas? > > >> > > >> cheers, > > >> > > >> Johannes > > >> > > >>> > > >>>> Cheers, > > >>>> Johannes > > >>>> > > >>>> _______________________________________________ > > >>>> grass-user mailing list > > >>>> grass-user@lists.osgeo.org <mailto: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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