Geometry Boost List: [geometry] Building difference between and MultiPolygon or Collection and Polygon

Subject: [geometry] Building difference between and MultiPolygon or Collection and Polygon
From: Stadin, Benjamin (Benjamin.Stadin_at_[hidden])
Date: 2017-04-19 15:33:40

Hi,

I want to cut out all smaller polygons which are within one larger polygon. I used GEOS for this, but due to performance issue with GEOS to build the difference I wanted to give BOOST a try. To give an example, the following works with GEOS. But it seems it needs to be worked around in BOOST Geometry, since the difference method doesn’t take a vector or geometry collection.

Example code using GEOS:

        const geos::geom::Geometry* cutGeometry = originalGeometry->clone();
        for (auto intersectIndexValue : intersects)
        {
            const geos::geom::Geometry *intersectCandidate = intersectIndexValue.second->geom();

            if (intersectCandidate->within(originalGeometry))
            {
                cutGeometry = cutGeometry->difference(intersectCandidate);
            }
        }

       double originalAreaSize = originalGeometry->getArea();
       double cutAreaSize = cutGeometry->getArea();
       // … do something if the cutted polygon is too small compared to the original

So the issue is that boost::geometry::difference() takes a single input geometry, a single geometry to build the difference against, and an output vector for the cut resulting geometry / geometries. But it doesn’t take a collection as input.

Is there an alternative and efficient way to build the difference between using input polygon collection instead of just a single polygon?

Regards
Ben