id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
8375	sym_difference of non-closed polygons returns closed polygon	Volker Schöch <vschoech@…>	Barend Gehrels	"The output multi-polygon from boost::geometry::sym_difference should have the same orientation, closed-ness and underlying scalar data type, as the input (multi-)polygons. My polygon type is oriented '''counter-clockwise''' and '''not closed''', my point type is based on '''int'''. Please find below some code that results in a '''closed''' polygon.

This is the data used as input to sym_difference:

{{{
_TPolygon<int> const polygonB =
	_TPolygon<int>(""MULTIPOLYGON(((813 277,1341 319,1863 361,2391 571,2913 361,3441 319,3963 277,3963 32767,813 32767)))"")
	^ _TPolygon<int>(""MULTIPOLYGON(((813 277,1341 319,1863 571,2391 571,2913 571,3441 319,3963 277,3963 32767,813 32767)))"");
}}}

This is the resulting multi-polygon, consisting of two closed polygons:

{{{
polygonB: MULTIPOLYGON(((2391 571,1863 571,1341 319,1863 361,2391 571)),((2391 571,2913 361,3441 319,2913 571,2391 571)))
}}}

This is my code that wraps boost::geometry to implement the operator used above:

{{{
template<typename T>
template<typename Geometry>
_TPolygon< T > _TPolygon< T >::operator^(Geometry const& geometry) const
{
       _TPolygon< T > polygonOut;
       boost::geometry::sym_difference(*this, geometry, polygonOut);

       // should not be necessary
       //boost::geometry::correct( polygonOut );

       return polygonOut;
}
}}}"	Bugs	closed	Boost 1.56.0	geometry	Boost 1.55.0	Problem	fixed	sym_difference, multi-polygon, polygon, closed, open, correct