Re: [gdal-dev] OGR Polygon Intersection

Kai Mühlbauer Sun, 28 Feb 2021 02:26:28 -0800

Hi,

thanks Darafei, I've found the news on OverlayNG. Also thanks to DanielBaston, who wrote me off list. Your help is very much appreciated.

So "normalize" would bring these polygons to their canonical form, whichis coordinates in lexicographic order, right? I'll just add this to mytestsuite.

@Even Rouault, I'd try adding "normalize" to GDAL OGR and pythonbindings, but my C/C++/SWIG knowledge might not be sufficient. If I'dtry anyway, what should I read to prepare?


Cheers,
Kai


Am 27.02.21 um 19:11 schrieb Darafei "Komяpa" Praliaskouski:

Please use GEOSNormalize / ST_Normalize or other equivalents beforecomparing geometries between library versions. The starting point in thering can change because of different optimizations, and GEOS 3.9 was acomplete rewrite of the geometry overlay subsystem.

On Sat, Feb 27, 2021 at 9:02 PM Kai Mühlbauer<[email protected] <mailto:[email protected]>> wrote:


    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

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--
Darafei "Komяpa" Praliaskouski
OSM BY Team - http://openstreetmap.by/ <http://openstreetmap.by/>


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