Wrong results for dissolve Polygon

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Wrong results for dissolve Polygon

Wimmer, Andreas
 
Dear Boost Geometry Contributors,
 
I am testing the boost::geometry::dissolve function upon some invalid polygons that are produced by a certain in-house segmentation alg.
The fact that the algorithm is producing possibly invalid polygons cannot be changed easily so I thought I will fix them afterwards using dissolve from “geometry/extensions/algorithms/dissolve.hpp” for the latest boost 1.58 version.
Unfortunately I stumbled over the following polygons for  which dissolve produces wrong results.
 
The following code illustrates the result
 
using namespace boost::geometry;
using namespace boost::geometry::model;
using namespace boost::geometry::model::d2;
 
int main(int argc, _TCHAR* argv[])
{
        polygon< point_xy<float> > Poly;
        read_wkt("POLYGON((10 10, 10 20, 20 20, 15 12, 15 18, 20 10, 10 10))",
                 Poly);
 
        multi_polygon< polygon< point_xy< float > > > Dissolved;
        boost::geometry::dissolve(Poly, Dissolved);
}
 
Which results in a polygon including the small intersection part which should be excluded from the polygon
And even more problematic the following example (same polygon with and additional self-touching outer ring) results in missing the entire main part of the polygon
 
int main(int argc, _TCHAR* argv[])
{
        polygon< point_xy<float> > Poly;
        read_wkt("POLYGON((10 10, 10 20, 20 20, 20 25, 22 25, 20 20, 15 12, 15 18, 20 10, 10 10))",
                 Poly);
 
        multi_polygon< polygon< point_xy< float > > > Dissolved;
        boost::geometry::dissolve(Poly, Dissolved);
}
 
I hope somebody can show me what I did wrong or what I can to too work around this problem.
 
Best regards,
 
 
Andreas Wimmer
 
 
 

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