Crash when processing a post-processed shapenet file

[noamgat]

Hi,
I've postprocessed shapenet models, using the mesh fusion ( https://github.com/davidstutz/mesh-fusion ) library, in order to add "thickness" to the shapenet model to avoid very thin regions.

Here is an example:
u1e22cc04-7c4d-4ed5-bda3-8ff8067f22ee.zip

When I later try to simplify them (and keep them watertight), I get a crash with the simplify tool:

simplify -i u1e22cc04-7c4d-4ed5-bda3-8ff8067f22ee.obj -o u1e22cc04-7c4d-4ed5-bda3-8ff8067f22ee_65536.obj -m -f 65536

simplify: /home/noamgat/hdd/Manifold/3rd/igl/per_vertex_point_to_plane_quadrics.cpp:83: igl::per_vertex_point_to_plane_quadrics(const MatrixXd&, const MatrixXi&, const MatrixXi&, const MatrixXi&, const MatrixXi&, std::vector<std::tuple<Eigen::Matrix<double, -1, -1, 0, -1, -1>, Eigen::Matrix<double, 1, -1, 1, 1, -1>, double> >&)::<lambda(const RowVectorXd&, const MatrixXd&, double)>: Assertion `std::abs(S.row(j).dot(ei)) < 1e-10' failed.
Aborted (core dumped)

This is consistent across all models. They are watertight (MeshlabServer is able to compute their volume, which is only possible for watertight meshes).

Any idea why this is happening?

[hjwdzh]

I believe this is the problem of the libigl library. I also had this problem before when the triangle is degenerated, e.g., the length of some certain edges is smaller than 1e-10. I think you could check whether you have such edges, and if so, this should probably be the problem.

[noamgat]

Assuming this is the case, how would you advise to work around this issue?

…

On Thu, Nov 21, 2019 at 8:21 PM Jingwei Huang ***@***.***> wrote: I believe this is the problem of the libigl library. I also had this problem before when the triangle is degenerated, e.g., the length of some certain edges is smaller than 1e-10. I think you could check whether you have such edges, and if so, this should probably be the problem. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#5?email_source=notifications&email_token=AAKFA2ALQK2O4TG6CV5C7NDQU3GSXA5CNFSM4JP7SL3KYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEE3FXOI#issuecomment-557210553>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAKFA2CKKGVURM6EVRJFCZTQU3GSXANCNFSM4JP7SL3A> .

[hjwdzh]

Maybe consider implementing the simplify yourself, or change the libigl code a little bit, or remove degenerated triangles in the mesh (which I think is the most difficult option).