On Fri, Aug 07, 2009 at 09:49:41AM -0500, Kenneth Marshall wrote:
> On Fri, Aug 07, 2009 at 09:12:34AM -0500, Kenneth Marshall wrote:
> > On Fri, Aug 07, 2009 at 11:29:47PM +1000, Paul Matthews wrote:
> > > We have two points with a finite separation in the x axis.
> > > Postgres thinks they are not the same point, nor one left of the
> > > other, nor to the right. This is clearly a both a physical and
> > > logical impossibility.
>
> Actually, quantum theory will allow this to happen. :)
I'm not a physicist, but I don't think it does. QM defines the
probability distribution within which the particle will be found. Once
you've actually observed both "points" you will know their physical
relation--you'll also have given them energy them so next time you look
they'll be somewhere else, but the act of observation causes the above
distribution to be collapsed. This sidesteps the whole issue of the
fact that points in PG are defined in euclidean space and do indeed
have a definite location and can be compared at all times---they don't
arbitrarily go jumping off millions of miles away or being annihilated
by their anti-particle just because it's possible.
I would agree with Paul that EPSILON is a hack and probably should be
removed. However it will cause user visible changes so it's not quite
as simple as that to change. I don't have anything really very useful
to add apart from saying that maybe the default should be the other way
around?
-- Sam http://samason.me.uk/