bg::union_(ring,ring) returns wrong result

[Mitsuhiko-Matsukawa]

boost1.80, Visual Studio 2017

void Test()
{
    namespace bg = boost::geometry;
    using point = bg::model::point<double, 2, bg::cs::cartesian>;

#if 0
    //correct result
    bg::model::ring<point> ring0 = {
        { 981,98 },
        { 927,0 },
        { 970,98 },
        { 981,98 }
    };

    bg::model::ring<point> ring1 = {
        { 927,0 },
        { 981,98 },
        { 995,98 },
        { 927,0 }
    };
#else
    //wrong result
    bg::model::ring<point> ring0 = {
        { 981.792858339935151,98 },
        { 927.152135631899114,0 },
        { 970,98 },
        { 981.792858339935151,98 }
    };

    bg::model::ring<point> ring1 = {
        { 927.152135631899114,0 },
        { 981.792858339935151,98 },
        { 995,98 },
        { 927.152135631899114,0 }
    };
#endif

    bg::model::multi_polygon<bg::model::polygon<point>> result;
    bg::union_(ring0, ring1, result);

    auto area0 = bg::area(ring0);
    auto area1 = bg::area(ring1);
    auto area_result = bg::area(result);
    assert(std::max(area0, area1) < area_result );
}

[Mitsuhiko-Matsukawa]

If I input the above data, get_distance_measure is called at these parameters.

p1=(927.15213563189911, 0.0000000000000000);
p2=(981.79285833993515, 98.000000000000000);
p=(981.79285833993515, 98.000000000000000);

If p is equal to p1 or p2, the distance should be 0. However, it returns 1.4551915228366852e-11.
If I fix this function and return 0, the result will be correct.

c1b8dbb

[Mitsuhiko-Matsukawa]

It might be better to fix handle_imperfect_touch .
We need a tolerance.

[barendgehrels]

Thanks for the report. I can reproduce it and I am considering your solution.

[barendgehrels]

It is fixed in a similar way as your fix, but slightly different to avoid regressions elsewhere.
Thanks again for the report and the analysis.