This polygon is valid according to the OGC SFS, and thus validates
correctly in PostGIS (also GEOS/JTS).
You'd have to look at the validation semantics of the other systems to
determine why they don't validate it. The OGC SFS model is fairly
tolerant in terms of trivial structural aspects - for instance, it
allows duplicate points. I believe this is done in order to allow as a
wide a range of geometries as possible to be represented, consistent
with topological integrity. Some other systems are less tolerant.
So I think strk is probably right - perhaps they don't allow duplicate
points, or perhaps they are reducing the precision and thus causing a
self-intersection (although I tried this in JTS, and reducing precision
doesn't actually cause self-intersections)
Martin
Rykov Denis wrote:
There is following polygon:
POLYGON((317371.62563763 5731575.49932608,
317028.110300846 5731043.43103426,
317028.110300846 5731043.43103426,
316389.822682815 5731138.79331604,
316478.209591618 5731705.00321977,
316478.209591619 5731705.00321977,
317350.223258488 5731584.46661525,
317371.62563763 5731575.49932608))
with two duplicate nodes. When I try to check it with ST_IsValidReason
function I get message
that it is Valid Geometry. Is this OGC compliant? When I try to check
it with QGIS, ArcView or
ArcGIS - I get notice about self intersection. Please explain this situation.
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Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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