On Sun, 31 Oct 2010 14:00:46 +0100, Borys Jurgiel wrote > Hi, > > In Spatialite layers, if I digitize a polygon counter-clockwise, the > ftools' geometry validity check says: > > Feature $n has incorrect node ordering > > Is it intentional, or a bug? It doesn't affect shapefiles. >
Hi Boris, in OGC-SFS specs there is absolutely no indication at all concerning the RING's node ordering (clockwise / counterclockwise). and this makes full sense, because for OGC POLYGONs the first RING always is the EXTERIOR ring, and any other subsequent RING (if present) has to be interpreted as an INTERIOR ring. this rule is absolutely clear and unambiguous: so there is no need at all to enforce a preferred node-ordering. AFAIK the nowadays obsolescent SHP format used a completely different rule: - the exterior ring has to be clockwise - any interior ring has to be counterclockwise - rings relative ordering is not relevant So I suppose that ftools (incorrectly) checks any polygon geometry for validity following the superseded SHP-like rules. But from the SpatiaLite's own perspective this makes no sense at all, because node ordering is absolutely irrelevant in this case. bye Sandro _______________________________________________ Qgis-developer mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-developer
