[postgis-users] OpenGIS Compliance Documentation

[Mateusz Loskot]

On 24 October 2013 01:31, BladeOfLight16 <bladeoflight16 at gmail.com> wrote:
> I was looking at this page today:
>
> http://postgis.refractions.net/docs/using_postgis_dbmanagement.html#OGC_Validity


FYI, the only official project site is postgis.net, so
http://postgis.net/docs/manual-2.0/using_postgis_dbmanagement.html#OGC_Validity


> This is a wonderfully simple explanation of what constitutes validity and
> simplicity with regards to geometries. However, I noted that this page
> doesn't seem to address problems with POLYGONs like when the exterior ring
> is self intersecting. For example, this query:
>
> SELECT ST_IsValidDetail(ST_GeomFromText('POLYGON((0 1,1 1,1 0,-1 0,-1 -1,0
> -1,0 1))'));
>
> correctly yields
>
> (f,Self-intersection,010100000000000000000000000000000000000000)
>
> Maybe I'm missing something in the documentation, but I don't see anything
> that directly indicates that this would be considered invalid. Maybe it's
> assumed that this would not be considered a POLYGON at all since a POLYGON
> must be simple? I'm not really sure. I think some kind of clarification is
> in order regardless of what kind. It seems that polygon rings must adhere to
> the simplicity requirements for line strings. Maybe that could be mentioned?

It is described in words. I  believe, these two make the whole picture:

"a simple geometry is one that has no anomalous geometric points, such
as self intersection"

"boundary of a POLYGON may intersect at a POINT but only as a tangent"

Best regards,
-- 
Mateusz  Loskot, http://mateusz.loskot.net