Error in difference between two polygons about nettopologysuite HOT 4 CLOSED

What is JTS' result? I suspect it is a precision problem.

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@FObermaier same suspect. I wanna check jts results first.

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checked: jts'trunk returns same results

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We also checked JTS with the same result. After some investigation it turns out its due to our implementation. We did calculate an intersection and then in a second step tried to remove the intersection from the geometry.
The problem is that one point is exactly on the line between two vertices and then the pricision model when rounding the coordinates moves the line between the two vertices slightly, and then if the intersection point is inside the geometry it creates a tail.

So strictly speeking the algorithm is correct and you just have to be carefull when using calculated geometries and instead of calculating an overlap and then removing that overlap, then just remove it by using the difference between the two original geometries

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