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From: "Kevin Grittner" on 22 Mar 2010 12:01
Simon Riggs <simon(a)2ndQuadrant.com> wrote:

> Yes, for most people touching != overlap. So it just looks like a
> bug.

A quick search of the web turned up a definition of overlap in
geometry as meaning that two polygons share at least one *internal*
point, which would be consistent with your interpretation; but there
is the issue of breaking existing code. Perhaps people are now
accustomed to following the existing overlaps test with a test that
the area of intersection is non-zero?

Anyway, based on what I found, we should document the current
behavior, as the term in PostgreSQL doesn't seem to match the
conventional definition in geometry.

-Kevin

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From: Andrew Dunstan on 22 Mar 2010 12:02


Simon Riggs wrote:
>>
>> Basically, what you feel is missing is documentation that if two
>> shapes share one or more points they are considered to overlap;
>> there is no requirement that they share an area?
>>
>
> Yes, for most people touching != overlap. So it just looks like a bug.
>
>

I guess I must be strange, then, it doesn't strike me as particularly
unnatural. By all means document it, though, if the docs are not clear
on the point.

cheers

andrew

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From: David Fetter on 22 Mar 2010 13:25
On Mon, Mar 22, 2010 at 04:47:37PM +0000, Simon Riggs wrote:
> On Mon, 2010-03-22 at 09:00 -0700, David Fetter wrote:
>
> > > Yes, for most people touching != overlap. So it just looks like a
> > > bug.
> >
> > I don't know which people you've surveyed, but at least in my math
> > classes, one point in common was sufficient for an overlap. I'd be
> > happy to write up something that makes this clear.
>
> If you're happy to document it, good, thanks.

I'm seeing a lot of places where this might be documented. Any ideas
as to which ones are appropriate?

Cheers,
David.
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From: Tom Lane on 22 Mar 2010 13:46
David Fetter <david(a)fetter.org> writes:
> I'm seeing a lot of places where this might be documented. Any ideas
> as to which ones are appropriate?

I would think "Geometric Functions and Operators" would be the most
appropriate spot ...

regards, tom lane

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From: David Fetter on 22 Mar 2010 13:55
On Mon, Mar 22, 2010 at 01:46:51PM -0400, Tom Lane wrote:
> David Fetter <david(a)fetter.org> writes:
> > I'm seeing a lot of places where this might be documented. Any ideas
> > as to which ones are appropriate?
>
> I would think "Geometric Functions and Operators" would be the most
> appropriate spot ...

Please find patch enclosed. :)

Cheers,
David.
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