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Panic in polygon difference #913
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I ran into the same issue doing a union:
The panic is the same:
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I’m out of action (🤒) rn, but we might try testing these errors against HEAD to see whether the recent fixes are relevant here? |
The HEAD version does indeed fix this issue. Thanks and hope you feel better! |
After returning to my original code using the HEAD version, I found a different example of the same issue. This one fails non-deterministically so you might have to do Example code is really long, click here to see it
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Unfortunately, my application also still produces panics when using the latest commit of this library.
results in the output:
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I thought I left a response on this long ago, sorry for letting the thread drop. Unfortunately I didn't take very good notes either, but as I recall the root of the issue was a lack of available precision. A little more specifically: With B.O. we maintain an invariant of visiting intersections and vertices in a certain order - (the "sweep" is monotonic). We can robustly compute when there is an intersection, but we also need to store the actual (X,Y) value of that intersection so we can order it WRT to our other crossings, to maintain the invariant that we're sweeping monotonically. However, because our floating point representation is finite, the number that we store may entail some error. IIRC, this panic is happening when we have two very close intersections, such that the amount of error in the f64 representation of the intersection is enough to break the monotonicity of the sweep. Like if we are trying to visit numbers in increasing order and we have: If we were trying to visit them monotonically, we might get it wrong. Anyway, not sure if this is helpful to anyone or if I'm even remembering the issue correctly, but I wanted to record my discoveries in case it's helpful for someone down the line. |
Looking at my debug branch a bit, I think this might be related to our usage of |
Implemented all the listed failed cases in this issue as test cases for a new implementation of the algo here a6184b1 and all the tests succeed. |
I get a panic when executing the following code:
The panic looks like this:
I use version 0.23.0 of the geo library with rustc 1.64.0.
I use the intersection and following difference because I need the boolean operation A & ~B which is not directly present in the included boolean operations as far as I could see.
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