Martin Davis wrote: > But, I think there is a bit of good news. I'm pretty sure that if you > are querying in lat-long space, relationships like ST_contains end up > being *more inclusive*. (I.e. you may get points returned which > wouldn't actually lie in the geometry if it was densified). This is due > to the fact that the spheroid "blows up like a balloon" and curves lines > outward. This is probably better than the alternative of being *less > inclusive*.
I disagree: Take polygons A and B, completely disjoint but with a shared boundary. Take point Z contained by polygon A in geodetic space. We've said polygon B can be more inclusive in planar space and include point Z. ST_contains will never say that A and B both contain point Z. Point Z has therefore switched polygons. > > This also means that there is no problem using the standard PostGIS > spatial index on geodetic data - the index is only an approximation > anyway, so as long as it doesn't lose geometry (which it won't by the > argument above) it will work fine. > I think because the edges of bounding boxes used by the index are effectively meridians and parallels, the spatial indexes are a different case, so we may be OK here? Cheers, Will _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
