Add mollification step to avoid degenerate faces #5037
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Degenerate faces (which can cause an infinite loop in `loop_over_edges`) are handled by using the mollification step described in section 4.5 of N. Sharp & K. Crane "A Laplacian for Nonmanifold Triangle Meshes" (2020). The tolerance value is set to 1/1000 of the minimum non-zero edge length.
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Heat_method_3/include/CGAL/Heat_method_3/internal/Intrinsic_Delaunay_triangulation_3.h
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…launay_triangulation_3.h Co-authored-by: Sebastien Loriot <sloriot.ml@gmail.com>
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What is waiting for approval ? |
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@janetournois will have a look. |
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@janetournois Is this PR replaced by #5033? |
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Thanks @oboes for this PR! |
thanks to mollification step
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Thanks @oboes ! |
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There are conflicts with master |
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@janetournois what is the status of this PR? Ready to be tested? |
…-oboes # Conflicts: # Heat_method_3/test/Heat_method_3/CMakeLists.txt
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It's ready (again) to be tested |
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@janetournois What is the |
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nothing left :-) @lrineau |
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@MaelRL This PR is marked as "not yet approved", is it still the case ? |
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@janetournois worked on it and is done with it, so I guess it can be cleared. |
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successfully tested in https://cgal.geometryfactory.com/CGAL/testsuite/results-5.3-Ic-98.shtml |
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Summary of Changes
This PR fixes the infinite loop problem from issue #5010 by implementing the "mollification" step from
N. Sharp & K. Crane "A Laplacian for Nonmanifold Triangle Meshes" (2020) (section 4.5).
Basically, the problem arises from degenerate faces (triangles) in the input mesh. These degenerate faces can be "removed" by increasing the length of all edges in the mesh by a small, constant amount
epsilonuntil no input triangle is degenerate. This constant depends on a user-defined tolerance valuedelta, which is the tolerance with which we want the (strict) triangle inequality to hold in each triangle. According to the paper, this method will not significantly distort the Laplacian of the mesh.The paper does not discuss the choice of the user-defined tolerance
delta. I decided to use an arbitrary value of(min_length*1e-4)wheremin_lengthis the minimum non-zero edge length in the mesh. This seems to work well enough, and in any case if the mesh is already free of degenerate faces to begin with, the mollification step should not change the end result.Release Management