Re: [jts-dev] Struggling with polygon topology again. Overlapping inner

[Martin Davis <mtnclimb@xxxxxxxxx>]

Not sure why the first version of the code would not work - it *looks* functionally identical to the second version.

You shouldn't have to use the OverlayOp class directly - not the best JTS style (although supported by the API, might not be as stable as the Geometry method).

The reason a MultiPolygon is returned is exactly what you see in the image.  3 holes touch and surround a disconnected area, which creates an extra polygon when the final one is subtracted.

On Mon, Sep 19, 2016 at 8:14 PM, Phil Scadden <p.scadden@xxxxxxxxxx> wrote:

Hmm, this version works;

                Polygon op = geometryFactory.createPolygon(p.getExteriorRing().getCoordinates());
                Geometry g = op;
                for (k=0;k<p.getNumInteriorRing();k++) {
                   Polygon ip = geometryFactory.createPolygon(p.getInteriorRingN(k).getCoordinates());
                   g = OverlayOp.overlayOp(g, ip, OverlayOp.DIFFERENCE);
                }


Now just need to figure out why the output geometry is a multipolygon...

--
Phil Scadden, Senior Scientist GNS Science Ltd 764 Cumberland St, Private Bag 1930, Dunedin, New Zealand Ph +64 3 4799663, fax +64 3 477 5232

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