exception in polygon.cpp

[makc]

As discussed previously, here is example input leading to:

Error in file: ...\manifold\polygon\src\polygon.cpp (599): 'skipped.empty() || !vert->IsPast(skipped.back(), precision_)' is false: Not Geometrically Valid! None of the skipped verts is valid.

a.obj:

v 0.000000 0.000000 0.000000
v 0.000000 230.000000 0.000000
v -1630.000000 230.000000 0.000000
v -1400.000000 0.000000 0.000000
v 0.000000 0.000000 -2143.000000
v -1630.000000 230.000000 -2143.000000
v 0.000000 230.000000 -2143.000000
v -1400.000000 0.000000 -2143.000000
f 1 2 3
f 3 4 1
f 5 6 7
f 6 5 8
f 7 3 2
f 7 6 3
f 6 4 3
f 6 8 4
f 8 1 4
f 8 5 1
f 5 2 1
f 5 7 2

b.obj:

v -1185.000000 -70.000000 -2143.000000
v -305.000000 -70.000000 -2143.000000
v -1185.000000 -70.000000 0.000000
v -305.000000 -70.000000 0.000000
v -1185.000000 15320.000000 0.000000
v -305.000000 15320.000000 -2143.000000
v -1185.000000 15320.000000 -2143.000000
v -305.000000 15320.000000 0.000000
v -1185.000000 460.000000 0.000000
v -305.000000 460.000000 0.000000
v -1185.000000 460.000000 -2143.000000
v -305.000000 460.000000 -2143.000000
v -1185.000000 160.000000 -2143.000000
v -305.000000 160.000000 0.000000
v -1185.000000 160.000000 0.000000
v -305.000000 160.000000 -2143.000000
f 1 2 3
f 4 3 2
f 5 6 7
f 6 5 8
f 3 7 1
f 5 7 3
f 4 5 3
f 8 5 4
f 2 8 4
f 6 8 2
f 1 6 2
f 7 6 1
f 9 10 11
f 12 11 10
f 13 14 15
f 14 13 16
f 11 15 9
f 13 15 11
f 12 13 11
f 16 13 12
f 10 16 12
f 14 16 10
f 9 14 10
f 15 14 9

here is what they look like:

the exception happens when we try to get the result of a - b.

[makc]

I assume there is a problem in b's bottom area, where some small triangles seem to sit on top of large ones 🤔 despite this mesh passing manifold test.

[makc]

Looking at it further, it is actually whole 2nd box there:

I guess it boils down to what you said here:

I don't currently make any guarantees about handling self-overlapping input meshes, and I don't have an efficient way to test for them either. I would like to make an algorithm to fix these, but that'll take considerable time. Until then, general input meshes aren't going to be safe.

[elalish]

Indeed, you are correct. I really need at least a decent self-overlap checker method. I might just turn that exception into one that says: "self-overlapping input detected, which is not supported". I only haven't because it's possible it could also be a legit bug, though I haven't found any recently.

[makc]

I guess I will close this one since it has to be fixed on web-ifc side.