create_exterior_skeleton_and_offset_polygons_2 stucks

[HunorSzabo]

Issue Details

Calling CGAL::create_exterior_skeleton_and_offset_polygons_2 for a "simple polygon stucks.

• Code works if I use less precision see commented out x,y arrays, but it's not a good solution I suppose.
• Also seem to work if I skip orientation but that also doesn't feel like the proper solution to me.

Just run/see code below to reproduce to simply reproduce, tried with and older 4.13 CGAL version and noticed on windows that it also thorws some "Microsoft C++ exception: CGAL::Uncertain_conversion_exception at memory location 0x000000CAD34FE3D0", not on Linux though with the most recent version.

Thank you for your time and effort, highly appreciated!

Source Code

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Polygon_2<K>   CGALPolygon;
void testCGAL() {
	/*const double x[28] = { 3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,3.4641,-6.52835e-17,-6.33865e-17,-5.78057e-17,-4.88654e-17,-3.70853e-17,-2.31499e-17,-7.86906e-18,7.86906e-18,2.31499e-17,3.70853e-17,4.88654e-17,5.78057e-17,6.33865e-17,6.52835e-17,3.4641, };
	const double y[28] = { 16.9915,15.4955,13.0989,9.94113,6.20559,2.10939,-2.10939,-6.20559,-9.94113,-13.0989,-15.4955,-16.9915,-17.5,-19.5,-18.9334,-17.2664,-14.596,-11.0773,-6.9148,-2.35047,2.35047,6.9148,11.0773,14.596,17.2664,18.9334,19.5,17.5, };*/
	double x[28] = { 3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,3.4641015529632568,-6.5283512761760263e-17,-6.3386490615069335e-17,-5.7805677252904074e-17,-4.8865411228468343e-17,-3.7085263204542273e-17,-2.314985300804045e-17,-7.8690580132517397e-18,7.8690580132513576e-18,2.3149853008040067e-17,3.7085263204541891e-17,4.8865411228467961e-17,5.7805677252903704e-17,6.3386490615068965e-17,6.5283512761759894e-17,3.4641015529632568, };
	double y[28] = { 16.991481781005859,15.495480537414551,13.09893798828125,9.9411334991455078,6.2055854797363281,2.1093919277191162,-2.1093919277191162,-6.2055854797363281,-9.9411334991455078,-13.09893798828125,-15.495480537414551,-16.991481781005859,-17.5,-19.5,-18.933364868164063,-17.266391754150391,-14.595959663391113,-11.077262878417969,-6.9147953987121582,-2.3504652976989746,2.3504652976989746,6.9147953987121582,11.077262878417969,14.595959663391113,17.266391754150391,18.933364868164063,19.5,17.5, };
	CGALPolygon cgalPolygon;
	typedef boost::shared_ptr<CGALPolygon> PolygonPtr;
	for (int i = 0; i < 28; ++i) {
		auto point = K::Point_2(x[i], y[i]);
		cgalPolygon.push_back(K::Point_2(x[i], y[i]));
	}
	if (cgalPolygon.is_clockwise_oriented()) {
		cgalPolygon.reverse_orientation();
	}
	std::vector<PolygonPtr> exteriorSkeleton = CGAL::create_exterior_skeleton_and_offset_polygons_2(1e-5, cgalPolygon);
	std::cout << "Uncreachable point";
}

Environment

• Operating system: Windows/Linux, 64 bits):
• Compiler: Visual Studio, GCC
• Release or debug mode: Debug/Release
• Specific flags used: none
• CGAL version: 5.0.2, 4.13
• Boost version: 1.6.8

Here is the polygon plot by vtk,

[HunorSzabo]

@sloriot I read it in one of your comment back 2014 that "This CGAL package requires the input polygon (with holes) to be non-degenerate, strictly-simple, and oriented counter-clockwise."
Do I need to use reverse_orientation(); before calling create_exterior_skeleton_and_offset_polygons_2?

[HunorSzabo]

@sloriot even a temporary tip would suffice and appretiated

[sloriot]

You can try using the function filtering collinear points introduced in #2920. I'm planning on working on the package next month.

[HunorSzabo]

thanks for the tip @sloriot will try today!
Is counterclockwise orientation still required?

[sloriot]

Yes otherwise interior and exterior are swapped

[afabri]

The PR #4905 fixes this problem.