CGAL users discussion list

["Laurent Rineau (GeometryFactory)" <>]

On mercredi 05 octobre 2011 10:21:46 Maarten Moesen wrote:
> Dear all,
> 
> I'm currently trying out the sharp-feature preservation of CGAL's 3D mesh
> generator on a 32-bit machine with MSVC 2008 (version 3.8, with Laurent
> Rineau's Triangulation_data_structure_3.h patch applied). My test geometry
> is a box having a big sphere cut out from its center. I add  as 1D sharp
> features  using line segments the circles where the sphere cuts the sides
> of the box, as well as the ribs of the box. Unfortunately, the mesher does
> not preserve all the features near the circle... most of the times a few
> segments are missing. The sample code is below. An example mesh is also
> attached.

Hi Maarten,

Thanks for your complete report. I was able to reproduce your experiment 
easily.

Actually the sharp features are preserved: "missing" segments are actually in 
the 3D complex. What is missing is the two incident facets!

Your domain is defined as an implicit surface (iso-surface of a function). 
Because of that, even if the surface of the domain can be decomposed into 
patches (separated by sharp curves), the "surface_patch_index" is the same 
for 
all triangles of the mesh. If your domain was able to tag surface patches 
differently, with different surface indices, then the topological criterion
  CGAL::parameters::facet_topology=CGAL::FACET_VERTICES_ON_SAME_SURFACE_PATCH
could "fix" the issues you have around sharp curves that correspond to a 
small 
angle (say, less than 30°).

Another way of fixing that is by decreasing the ratio edge_size/facet_size, 
or 
decreasing the facet_distance.

-- 
Laurent Rineau, PhD
R&D Engineer at GeometryFactory           http://www.geometryfactory.com/
Release Manager of the CGAL Project       http://www.cgal.org/