Hi Markus, Micha, Many thanks for your emails, the combined solution that you suggested worked perfectly.
best regards, Daniel. On 25/08/18 11:03, Markus Metz wrote: > > > On Sat, Aug 25, 2018 at 10:56 AM Micha Silver <tsvi...@gmail.com > <mailto:tsvi...@gmail.com>> wrote: > > > > I think I have a series of steps that will allow you to separate the > "inner" boundaries and generalize only those. The idea is based on > using the v.to.db module, with the "sides" option to add the cat > number of each area to the left and right of each boundary. Outer > boundaries will have "-1" (nothing on that side) for the left or right > sides. Then you can split out the inner boundaries with a v.extract > using a "where" clause. > > nice approach, but it could be simplified because v.generalize has a > where option, i.e. no need for v.extract: > > > > Somewhat convoluted, but here you are as regular grass command, not > in python. > > > > (My example below is from the sample nc_basic_spm_grass7 location. I > tested with the geology map.) > > > > # Make a copy and add cats to the boundaries in layer 2 > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > g.copy vect=geology,my_geol > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.category my_geol layer=2 > type=boundary option=add output=my_geol2 > > > > # Add attribute columns for the left and right sides in layer 2, and > populate from the areas in *layer 1* > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.db.addtable my_geol2 layer=2 > column="left integer,right integer" > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.to.db my_geol2 layer=2 > option=sides column=left,right query_layer=1 > > generalize inner boundaries > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.generalize input=my_geol2 > method=douglas output=my_geol2_smooth thresh=1000 type=boundary > layer=2 where="left > -1 and right > -1" --o > > done > > Markus M > > > > > # Now use the left and right cat value to separate the inner and > outer boundaries > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.extract my_geol2 layer=2 > out=inner_bndry type=boundary where="left<>-1 and right<>-1" > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.extract my_geol2 layer=2 > out=outer_bndry type=boundary where="left=-1 or right=-1" > > > > # Convert inner boundaries to lines for smoothing, and run generalize > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.type input=inner_bndry > out=inner_lines layer=2 from=boundary to=line > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.generalize inner_lines > method=douglas output=inner_lines_smooth thresh=1000 --o > > > > # Convert back to boundary and merge back with the outer boundary > and recreate area centroids > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.type inner_lines_smooth > out=inner_bndry_smooth from=line to=boundary layer=2 --o > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.patch > input=outer_bndry,inner_bndry_smooth output=merge_smooth --o > > GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.centroids merge_smooth > output=merged_areas layer=2 option=add > > > > > > You probably will have to do some manual cleaning of the result, > since the smoothed inner boundaries might no longer exactly intersect > with the untouched outer boundary due to overshoots, etc. > > > > If you try this, let us know how it went. > > > > Regards, Micha > > > > > > > > On 08/24/2018 06:43 PM, Daniel McInerney wrote: > > > > Hi List, > > > > I'm using v.generalize in a script (excerpt included below) to smooth > > the boundaries of a polygon vector dataset. In the attached example > > (input_vector.png), I would like to *only* generalize the internal lines > > (blue), and leave the external boundary (green line) unchanged. I > > thought that the flag, '-l' might provide this functionality, but > > unfortunately the resulting external boundary is changed significantly > > (attached vgeneralize_output.png). > > > > Is this functionality available in v.generalize or is there another way > > that this could be achieved in GRASS? > > > > Thanks in advance. > > > > Best regards, > > Daniel. > > > > ##run generalisation (step: 1 - douglas) > > gscript.run_command('v.generalize', flags='l', overwrite=True, > > input='segments', output='segments_douglas', method='douglas', > threshold=1) > > > > ##run generalisation (step: 2 - sliding average) > > gscript.run_command('v.generalize', flags='l', overwrite=True, > > input='segments_douglas', output='segments_douglas_slide', > > method='sliding_averaging', threshold='2', look_ahead='9', slide='0.1', > > iterations='3') > > > > ##run generalisation (step: 3 - snake) > > gscript.run_command('v.generalize', flags='l', overwrite=True, > > input='segments_douglas_slide', output='segments_douglas_slide_snake', > > method='snake', threshold='3', alpha='1', beta='1') > > > > > > > > > > > > _______________________________________________ > > grass-user mailing list > > grass-user@lists.osgeo.org <mailto:grass-user@lists.osgeo.org> > > https://lists.osgeo.org/mailman/listinfo/grass-user > > > > > > -- > > Micha Silver > > Ben Gurion Univ. > > Sde Boker, Remote Sensing Lab > > cell: +972-523-665918 > > > > _______________________________________________ > > 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
