On Fri, Mar 31, 2006 at 12:04:39AM +0200, Mateusz £oskot wrote: > Martin Davis wrote: > > Yes. The spec doesn't cover this, but I chose to use an empty > > GeometryCollection as a "typeless" empty geometry, for methods which > > need to return one. The createEmptyGeometry method is just a > > convenience method for this convention. > > OK, I understant it. > > > Anyway, what else could that method return that would make sense > > (given that it has no type information)? > > It depends on the idea behind "empty geometry" or "null geometry" [1]. > As I know, OGC Simple Feature Spec. explains that empty geometry > represents empty point set (empty set of coordinates). > According to my understanding: > Point is empty if it contains "uninitialized" coordinates > MultiPoint is empty if it contains no points in its set. > etc. > > There is also a distinction between empty and null. > NULL means something undefined, uninitialized - something unsafe. > EMPTY means something well constructor but with empty set of points. > In some case, NULL object can be compared to EMPTY object with true result.
But what's defined in an EMPTY set of points ? It's the points themself giving semantic of a geometry type. What distinguish an EMPTY point from an EMPTY line from an EMPTY collection ? It's the exactly same topological space: the NO space at all. How can you say that NOTHING is a point or a line or an area ? --strk; _______________________________________________ geos-devel mailing list geos-devel@geos.refractions.net http://geos.refractions.net/mailman/listinfo/geos-devel
