[postgis-users] Problem : Within() incorrectly returns 'false'

[Brent Wood]

Mark Leslie a écrit :
> Arnaud,
> I've managed to track down the bug.  It seems that the algorithm
> determines any point to be within a zero length segment, which your
> polygon had a pair of.
> I've made the fix and committed it.

A zero length segment implies a duplicate vertex. 

I understood such a situation to be an invalid topology, so should get picked
up by isvalid(). Where a feature is invalid() a wrong answer from a query is
always possible, and is not necessarily a bug (although it is nice to get these
fixed :-)  

Are zero length segments one of the conditions picked up by isvalid()?

Cheers,

   Brent Wood