[gdal-dev] OGR Polygon Intersection

[Kai Mühlbauer]

Hi,

OK, I've found something here:

https://info.crunchydata.com/blog/waiting-for-postgis-3.1-geos-3.9

pointing out that a rewrite of the overlay engine in GEOS has taken place.

But I couldn't find anything describing the behaviour of how the first 
point of the intersection is determined. It looks like it skips the 
first point and takes the second. At least my example indicates that.

So my questions would be, is this something which can be relied upon in 
the future and why was this change necessary.

Thanks for any input here.

Cheers,
Kai





Am 27.02.21 um 18:02 schrieb Kai Mühlbauer:
> Hi,
> 
> this might be a silly problem or no problem at all, but I currently 
> can't wrap my head around it.
> 
> I'm using python bindings of GDAL OGR with GEOS support for layer 
> intersection since several years now. Now suddenly my testsuit which 
> checks intersection of two boxes breaks since the intersecting box 
> starts now with a different starting point (all four points of the box 
> fit with the earlier tests).
> 
> The change took place between versions GDAL 3.2.0 -> 3.2.1, GEOS 3.8.1 
> -> 3.9.1 and PROJ 7.1.1 -> 7.2.0. I've tried to find anything what might 
> have changed in the release notes of GDAL and GEOS, but couldn't.
> 
> So if anyone has a clue what's going on or what has changed and can 
> point me to the relevant resources, I would greatly appreciate it.
> 
> Below you find the geometries I uses as JSON strings and the differing 
> intersection.
> 
> src
> '{ "type": "Polygon", "coordinates": [ [ [ 1.0, 1.0, 0.0 ], [ 1.0, 2.0, 
> 0.0 ], [ 2.0, 2.0, 0.0 ], [ 2.0, 1.0, 0.0 ], [ 1.0, 1.0, 0.0 ] ] ] }'
> 
> trg
> '{ "type": "Polygon", "coordinates": [ [ [ 0.5, 0.5, 0.0 ], [ 0.5, 1.5, 
> 0.0 ], [ 1.5, 1.5, 0.0 ], [ 1.5, 0.5, 0.0 ], [ 0.5, 0.5, 0.0 ] ] ] }'
> 
> trg.Intersection(src) (GDAL 3.2.0, GEOS 3.8.1, PROJ 7.1.1)
> '{ "type": "Polygon", "coordinates": [ [ [ 1.0, 1.5, 0.0 ], [ 1.5, 1.5, 
> 0.0 ], [ 1.5, 1.0, 0.0 ], [ 1.0, 1.0, 0.0 ], [ 1.0, 1.5, 0.0 ] ] ] }'
> 
> trg.Intersection(src) (GDAL 3.2.1, GEOS 3.9.1, PROJ 7.2.0)
> '{ "type": "Polygon", "coordinates": [ [ [ 1.5, 1.5, 0.0 ], [ 1.5, 1.0, 
> 0.0 ], [ 1.0, 1.0, 0.0 ], [ 1.0, 1.5, 0.0 ], [ 1.5, 1.5, 0.0 ] ] ] }'
> 
> Thanks in advance!
> 
> Cheers,
> Kai
> 
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/gdal-dev