[Qgis-user] Multipolygons with errors ?
Hugues François
hugues.francois at irstea.fr
Sat Mar 30 08:32:22 PDT 2013
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:goyodiaz at gmail.com]
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 <dbakeman at comcast.net>:
> 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
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