[geos-devel] Re: [GEOS] #527: Union and UnaryUnion both fail at correctly node input lines

[Sandro Santilli]

On Mon, Apr 02, 2012 at 10:13:16PM -0700, Martin Davis wrote:
> JTS uses the FastNodingValidator to check for correctly noded line
> arrangements.  Basically it checks for any interior-interior segment
> intersections, using indexing to speed things up.
> 
> And yes, the OGC operation semantics aren't fully capable when it
> comes to more specific uses like checking noding.  That's one reason
> I introduced the boundary-node rule.
> 
> The Polygonizer is fine with closed lines (as long as, as always,
> the linework is FULLY noded).
> 
> This issue is just one more example of a robustness failure.

Do you think the use of a selected Noder might handle such cases
better than relying on Union operation to do noding ?

It seems to me that GeometryGraph class (used by overlay ops)
uses EdgeIntersectionList and friends to perform noding, rather
than the "noding" package. I've been thinking that this specific
case of a noding failure could have been resolved by an
IteratedNoder (just guessing that the problem is in a splitting
node modifying an edge shape to cross another existing edge).

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