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[lien lee <>]

Hi Camille,

Yes, you are right.  The problem lies in my visualization software.  It's computes the surface normal direction by the order of the three vertice of  each triangle.  After using "  CGAL::output_surface_facets_to_off (out, c2t3, CGAL::Surface_mesher::NO_OPTION);
"  to output the off file to make the mesh oriented, the software shows the mesh normally as expected.

2009/10/7 Camille Wormser <>

[the list seems to have some troubles, I try to post my answer once more...]

I then run the example with the “mesh_a_3d_gray_image.cpp” without any modification made to the original code. The output “out.off” is at attached.  After removing the third empty line in the off file, the mesh is visualized as attached “out_grayimage.jpg”.  As can be seen, there are a lot of holes on the mesh (I don't think they are caused by back face culling since there is no triangle at the holws if I show the mesh in the mode of wireframe).

Hi,
In fact, this is a visualization problem, due to the orientation of the triangles: as you can see in the OFF file, there are 5270 vertices and 10544 (triangular) faces. Assuming that it is manifold (which is in fact the case), so that the number of edges can be deduced, you can compute that

euler_characteristic = v - e + f = -2  = 2 - 2g,

so that the genus appears to be 2. If you fix your visualization tool, you will see that it is in fact the case: one loop is represented by the jawbone, and the other loop comes from the nose.

If you look carefully, you will also see that the skull has a hole on the left temple (not a missing triangle: the mesh is still a manifold without boundary). This happens because the feature size provided to the algorithm is a bit too high (in comparison to the width of the bone layer): the internal and external surfaces cannot be properly separated by the algorithm in this region. Setting a lower feature size would prevent that from happening.

Best,
--
Camille

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