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This is an initial version of 3D-EPUG-OVERLAY, an algorithm for exactly (and efficiently) intersecting 3D triangulated meshes.

Warnings:

  • I intend to rewrite most of this code.
  • This code lacks a good documentation (a short term goal is to improve this).
  • The "main" reads/writes text off files (with triangulated meshes) with floating-point coordinates. Converting too/from floating-point coordinates may introduce errors in the mesh (thus, it could be a good idea to provide exact rational coordinates to the algorithm and get the resulting rationals before they are converted to floating-point numbers). There are some interesting papers mentioning the challenge of converting meshes with rational coordinates into meshes with floating-point coordinates.
  • This algorithm employs Simulation of Simplicity (a symbolic perturbation technique) to handle the special cases. This technique is very solid (it is not a numerical perturbation -- the perturbation is only "simulated" ). However, when the output is written to a file SoS is ignored:
    • This may generate artifacts in the output. For example: faces with area 0 (this area would be infinitesimal considering SoS), polyhedra with volume 0 (again, the volume would be infinitesimal considering the perturbation), etc.
    • A future work is to regularize the output meshes removing these artifacts (an alternative is to process them not ignoring the symbolic perturbations).

Restrictions:

  • The algorithm assumes the input meshes are valid (free of self-intersections, watertight, consistent). It may work with invalid meshes (but it is not guaranteed to work -- the output may be invalid, the program may crash, etc).

Compiling/running:

  • We employ the excellent CGAL library to do the computations with interval arithmetic (this accelerates the computations with rationals in the predicates).
  • This program also requires GMP.
  • This repository includes a Makefile (however, I still have to improve it...).
  • If you try to run the program without arguments it will print a small help message showing the required arguments.
  • Example of command line arguments:
    • ./meshIntersection 282_bimba_cvd.stl.off 203_vase.stl.off 64 8 1 out.off
    • The first and second arguments are the input meshes.
    • The third and fourth arguments are the resolutions of the first and second level grids (the optimum is very broad -- we typically use a heuristic to choose this resolution: g1 x g2 = power(100000 x m0 x m1,1/6), where g1*g2 is the product of the resolution of the two grids, m0 and m1 are the number of triangles in the two input meshes).
    • The fifth argument is the trigger for creating the second-level grid (again, the optimum is very broad -- we typically choose a small number for this).
    • The last argument is the output mesh.
  • This program uses OpenMP for running in parallel

Example of mesh intersection computation:

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