id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
12752	difference algorithm returning invalid geometry (regression over 1.59.0)	Volker Schöch <vschoech@…>	Barend Gehrels	"My ""tc::geo::polygon"" type is actually a '''multi-polygon''', using a polygon type that is based on '''int''', oriented '''counter-clockwise''' and '''open''' (not closed). Please consider the following example: 
{{{
tc::geo::polygon<int> polygonA;
boost::geometry::read_wkt(""MULTIPOLYGON(((3232 2413,2136 2646,3232 2412,3232 2413)),((3232 2532,3232 2856,1031 2856,1031 1056,3232 1056,3232 2221,2136 2328,1032 1212,1032 1458,1032 1764,2136 2790,3232 2532)))"", polygonA); // does not throw
_ASSERT( boost::geometry::is_valid(polygonA) ); // returns true

tc::geo::polygon<int> polygonB;
boost::geometry::read_wkt(""MULTIPOLYGON(((1032 2130,1032 1764,2052 2712,1032 2130)),((3234 2580,2558 2690,3234 2532,3234 2580)),((2558 2690,2136 2790,2052 2712,2136 2760,2558 2690)))"", polygonB); // does not throw
_ASSERT( boost::geometry::is_valid(polygonB) ); // returns true

tc::geo::polygon<int> polygonC;
boost::geometry::difference(polygonA, polygonB, polygonC); // does not throw
// polygonC: MULTIPOLYGON(((3232 2413,2136 2646,3232 2412,3232 2413)),((2568 2688,3232 2580,3232 2856,1031 2856,1031 1056,3232 1056,3232 2221,2136 2328,1032 1212,1032 1458,1032 1764,2052 2712,2136 2790,2568 2688),(1032 1764,1032 2130,2052 2712,1032 1764)),((2952 2598,3232 2532,3232 2533,2952 2598)))
boost::geometry::is_valid(polygonC); // returns false!
}}}
The difference of two valid multi-polygons yields an invalid multi-polygon.

May be related to tickets #10661, #11674, #11676, #12751.

This problem was NOT present in boost 1.59.0."	Bugs	closed	Boost 1.67.0	geometry	Boost 1.66.0	Problem	fixed	difference, multi-polygon, polygon