Pull the centroid of the geometry and use generate_series() / pointn() to "explode" the points and test each point for above & right of centroid, above and left of centroid, etc...
> -----Original Message----- > From: [email protected] > [mailto:[email protected]] On > Behalf Of Armin Burger > Sent: Thursday, February 26, 2009 11:57 AM > To: PostGIS Users Discussion > Subject: [postgis-users] order of points in ST_ConvexHull > > > Hello > > I need to find a possibility to identify upper-left, > upper-right, etc. > corners of +/- rectangular polygons. I.e. polygons with > guranteed just 4 > corners, but with a shape that is typically between a rectangle and a > rhomb. The polygons define the geometry of image boundaries ("image > footprints"). But it cannot be guaranteed which point in the polygon > corresponds to which corner since the order of points during geometry > creation is unknown. > > One idea was to use ST_ConvexHull(geometry) since for this > very simple > polygons the convex hull seems to be identical with the geometry. It > looked to me that the order in this convex hull was: > lower-right, lower-left, upper-left, upper-right > Does anybody know if this order is always like that or can this order > change? Would anybody know another method to identify which > point of the > polygon corresponds to which corner? > > Regards > > Armin > _______________________________________________ > postgis-users mailing list [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
