Re: [postgis-users] Overlapping of polygons with SimplifyPreserveTopology
On 11/12/13 19:15, Sandro Santilli wrote: A topological approach would solve it. Simplifying a polygon may overlap with the still-unsimplified adjacent one, so you can't check after each single simplification. You could check afterwards, at the end, but then resolving one overlap on one side may introduce another overlap in the other side. Really, you need to model your data topologically, then simplify edges, rather than full polygon boundaries. Actually, I simplified (with ST_SimplifyPreserveTopology) one edge at a time, but did not check at every step (I was under the impression that this function did preserve topology). See http://strk.keybit.net/blog/2012/04/13/simplifying-a-map-layer-using-postgis-topology/ Thanks, this did the trick. It would be useful to add it to PostGIS. Regards, Luca Morandini Data Architect - AURIN project Melbourne eResearch Group Department of Computing and Information Systems University of Melbourne Tel. +61 03 903 58 380 Skype: lmorandini ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
Re: [postgis-users] Overlapping of polygons with SimplifyPreserveTopology
On Tue, Dec 10, 2013 at 7:00 AM, Paolo Cavallini cavall...@faunalia.it wrote: Hi Luca, you really need to use full topology for this. ST_SimplifyPreserveTopology simply prevents topological errors, it does not guarantee sharing of nodes etc. Good luck. Exactly. So, two ways to go with this, so far: * use the PostGIS topology model * use GRASS, if your workflow let you move data in and out to the GRASS db cheers p -- Paolo Corti Geospatial software developer web: http://www.paolocorti.net twitter: @capooti skype: capooti ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
Re: [postgis-users] Overlapping of polygons with SimplifyPreserveTopology
On 10/12/13 17:00, Paolo Cavallini wrote: Hi Luca, you really need to use full topology for this. ST_SimplifyPreserveTopology simply prevents topological errors, it does not guarantee sharing of nodes etc. Thanks for your answer Paolo, but our issue is how prevent simplification when it yields overlapping polygons: could a universe polygon solve it ? Regards, Luca Morandini Data Architect - AURIN project Melbourne eResearch Group Department of Computing and Information Systems University of Melbourne Tel. +61 03 903 58 380 Skype: lmorandini ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
[postgis-users] Overlapping of polygons with SimplifyPreserveTopology
Folks, we noticed that, despite the use of ST_SimplifyPreserveTopology, non-adjacent polygons may overlap; this happens when there is a long and narrow water body of between them (think of a fiord), but this body is not itself a polygon. To solve this issue we came up with the idea of adding an universe polygon; that is, a polygon that enclose the entire extent of a table, so that every polygon has a left and right polygon: would this do the trick ? Regards, Luca Morandini Data Architect - AURIN project Melbourne eResearch Group Department of Computing and Information Systems University of Melbourne Tel. +61 03 903 58 380 Skype: lmorandini ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
Re: [postgis-users] Overlapping of polygons with SimplifyPreserveTopology
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Il 10/12/2013 04:49, Luca Morandini ha scritto: we noticed that, despite the use of ST_SimplifyPreserveTopology, non-adjacent polygons may overlap; this happens when there is a long and narrow water body of between them (think of a fiord), but this body is not itself a polygon. To solve this issue we came up with the idea of adding an universe polygon; that is, a polygon that enclose the entire extent of a table, so that every polygon has a left and right polygon: would this do the trick ? Hi Luca, you really need to use full topology for this. ST_SimplifyPreserveTopology simply prevents topological errors, it does not guarantee sharing of nodes etc. Good luck. - -- Paolo Cavallini - www.faunalia.eu QGIS PostGIS courses: http://www.faunalia.eu/training.html -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.15 (GNU/Linux) Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iEYEARECAAYFAlKmreQACgkQ/NedwLUzIr538QCePEiOoGaI2eSq9u8JsCviY77X 0bgAn0BrwdhOY0Ua4hnLmIWE/YdkLon3 =UWZJ -END PGP SIGNATURE- ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
