Reid Priedhorsky wrote:
Charlie Savage wrote:The 2 point could be spatially equal given different SRIDS and coordinates if they were projected to a common SRID. So shouldgeometry operators silently Call st_transform to make the righthand match the lefthand before comparing? This would be quite the expensive operation.No. You can't automatically transform between different SRID values Think of the case of one geometry with an SRID value of 4326 and onewith an SRID value of -1 (no coordinate system).Exactly.So different SRID values, then the geometries are not equal.No -- as Stanley said, the geometries could be in fact equal, but expressed in different SRS. So if ST_Equals() returned False, it would be wrong.
Maybe. But returning "Operation permitted" is even worse because it means you can't do natural things like this (without extra annoying SRID checking code) in plpgsql:
IF (geom1 == geom2) ... END IF; Or the example with the union earlier posted
It is up to the user to transform geometries to the same SRID before calling ST_EQUALS.Exactly. ;)
So, I still vote that st_equals will not blow up when comparing two geometries with different SRID values, it just will return false.
Charlie
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