union_() generates self-intersecting polygon

[max@…]

I have a program which generates unions of a multipolygon and a ring. Sometimes, I have an identical point in the two shapes. The union_ result is a self-intersecting polygon.

Demo source attached. Output with Boost 1.58 and 1.60:

input multipolygon is valid input ring is valid result multipolygon is invalid: Geometry has invalid self-intersections. A self-intersection point was found at (-95, 60); method: t; operations: i/i; segment IDs {source, multi, ring, segment}: {0, 0, -1, 3}/{0, 0, -1, 6}

[max@…]

Demo source for the union_ bug

[anonymous]

I think the problem is not union_() - the correct result is a polygon that "touches" itself (but does not actually intersect), and that's what union_() does. The problem may just be a false negative in is_valid().

[Barend Gehrels]

Thanks for the report. It is fixed in the branch feature/cluster_touch

• still hope to get it in 1.61 because it fixes more issues