[postgis-devel] Minimum number of points in a POLYGON ring?

[Mark Cave-Ayland]

Hi there,

Having just been working on the parser again, I've just wanted to verify 
we are currently doing the check for the minimum number of points in a 
polygon ring correctly.

Currently the parser enforces a minimum of 3 points in a ring - but 
given that the last point in a ring must be the same as the first point, 
do we need to increase this to 4? So in other words, is a polygon with 
no area simple?

A bit of googling shows Informix believes the minimum number of points 
in a polygon should be 4 (see USE31 in 
http://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=/com.ibm.spatial.doc/spat310.htm), 
but that doesn't distinguish between whether that is for the whole 
polygon or just an individual ring. Can anyone clarify this with the OGC 
spec?


Many thanks,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
T: +44 870 608 0063