Hello, I'm back after few time because of work and because I had to look deeper at OGC spec. to give a right answer.
After I read it the implementation standard (http://www.opengeospatial.org/standards/sfa) I definitively think the union of two polygons sharing a limited number of points result in a valid multipolygon since a multipolygon is defined as their elements' *interior* may not intersect and may touch at only a finite number of points. Furthermore, fig 12 and 17, draw an example similar to my case study to illustrate respectively an invalid polygon and (17c) a valid multipolygon. When QGis validity checker throw an error of this kind of multipolygon, I think it is wrong. Should I report a bug ? Hugues. -----Message d'origine----- De : Goyo [mailto:[email protected]] Envoyé : lundi 25 mars 2013 21:13 À : David J. Bakeman Cc : Hugues François; Quantam GIS Objet : Re: [Qgis-user] Multipolygons with errors ? 2013/3/25 David J. Bakeman <[email protected]>: > OK. So if I take your shape file and run Vector/Geometry > Tools/Singlepart to multipart. Then if two parts of a feature touch each other I think it's invalid again (as for the OGC-SFS). > Note grass doesn't report any topo errors on either the singlepart or > multipart shape files. This may be due to GRASS using a different geometry model. It validates against different criteria. Goyo _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
