CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 05/22/2018 08:33 PM, Zesen Qian wrote:
> Hi Sebastien,
>
> Thanks for this. I wrote the program myself and I'm using surface_mesh
> instead of mesh_3. Question: Why will Mesh_3 be faster? From what I
> understand this will not only generate facets but also cells inside
> the shape? How will that accelerate the process?
Mesh_3 code has been updated to take advantage of threads so it will be 
faster. Moreover, the code of Surface_mesh has not been updated for some
time now because we are planning to replace it with the implementation 
of Mesh_3. If you put no constraints on the tetrahedra, only the 
constraints on surface facets will make the mesh work more.

Sebastien.

> And in particular, if I'm not interested in the cells, how should I
> set the parameters concerning it? i.e., cell_radius_edge_ratio and
> cell_size.
>
> Best,
> Zesen
>
> On Tue, May 22, 2018 at 2:25 PM, Sebastien Loriot (GeometryFactory)
> <>
>  wrote:
> > Note that this PR : https://github.com/CGAL/cgal/pull/3043
> > will bring some noticeable speed up as well as parallel mesh algorithm.
> >
> > Best,
> >
> > Sebastien.
> >
> >
> > On 05/22/2018 07:18 PM, Zesen Qian wrote:
> > > Hi Sebastien,
> > >
> > > Sorry for keep spamming your inbox - but I found how to sample areas
> > > differently based on variety. For future reference, the parameter
> > > distance_bound constrols the max distance from every generated facet
> > > to the surface. So when the same value applies to different areas, the
> > > areas with more details will get sampled more.
> > >
> > > Thank you so much for the help!
> > >
> > > Best,
> > > Zesen
> > >
> > > On Tue, May 22, 2018 at 11:11 AM, Zesen Qian 
> > > <>
> > >  wrote:
> > > > Hi Sebastien,
> > > >
> > > > I think I was mistaken - I tried it again and it seems that I don't
> > > > have to do too much about the angle_bound - adjusting other parameters
> > > > would suffice to give a decent result.
> > > >
> > > > However, it is indeed slow. One feature of my mesh is that it donsn't
> > > > have to be evenly sampled - some areas require more details than
> > > > others.  Can I do some trick so that those area receive extra
> > > > sampling, while other more monotone area get less, so I can save some
> > > > processing time?
> > > >
> > > > Best,
> > > > Zesen
> > > >
> > > > On Tue, May 22, 2018 at 10:26 AM, Zesen Qian 
> > > > <>
> > > > wrote:
> > > > > Hi Sebastien,
> > > > >
> > > > > Thanks for this. I don't know if that's a similiar thing, but I tried
> > > > > https://doc.cgal.org/latest/Surface_mesher/
> > > > > by a distance function(with AABB_tree and side_of_triangle). Seen from
> > > > > the source code of the plugin, it's very similar.
> > > > >
> > > > > To get a decent result it's quite slow. If I set the angular bound to
> > > > > 90 degree(more than 30),  the algorithm is not garanteed to
> > > > > terminate(and indeed in my case). My mesh has some very thin layers
> > > > > that's easy  to be ignored by meshing, so I don't expect this method
> > > > > to work.
> > > > >
> > > > > What I'm now trying is simply using the "solidify" modifier in
> > > > > Blender, and fix the potential self-intersections using refining and
> > > > > outer-hull operation, and then use boolean operation with the original
> > > > > mesh to get a offseted mesh. I'm using libigl to do these tasks.
> > > > >
> > > > > Best,
> > > > > Zesen
> > > > >
> > > > > On Tue, May 22, 2018 at 9:59 AM, Sebastien Loriot (GeometryFactory)
> > > > > <>
> > > > >  wrote:
> > > > > > There is indeed nothing official in CGAL. However, in the Polyhedron
> > > > > > demo we wrote a small plugin that is meshing the distance function to a
> > > > > > mesh
> > > > > > and the output is by construction guaranteed to be free from
> > > > > > self-intersections. However sharp features are not correctly meshed if
> > > > > > not protected.
> > > > > >
> > > > > > Go into 3D Surface Mesh Generation -> Offset meshing once having loaded
> > > > > > a polyhedron.
> > > > > >
> > > > > > Source code is here:
> > > > > >
> > > > > > https://github.com/CGAL/cgal/blob/releases/CGAL-4.12-branch/Polyhedron/demo/Polyhedron/Plugins/Surface_mesh/Offset_meshing_plugin.cpp
> > > > > >
> > > > > > HTH,
> > > > > >
> > > > > > Sebastien.
> > > > > >
> > > > > >
> > > > > > On 05/17/2018 07:44 PM, Zesen Qian wrote:
> > > > > > > Hi list,
> > > > > > >
> > > > > > > I have a triangulated, closed mesh which is free of any degeneracies.
> > > > > > > Is there any reliable way to offset this mesh? By reliable I mean the
> > > > > > > result mesh should be free of any degeneracies.
> > > > > > >
> > > > > > > I searched on Internet and there is simply not an library/program
> > > > > > > available that can do this. I guess CGAL isn't capable of this either,
> > > > > > > but I believe people on this list should be familiar with this topic
> > > > > > > and maybe offer some comments.
> > > > > > >
> > > > > > > Thank you.
> > > > > > >
> > > > > > > Best,
> > > > > > > Zesen
> > > > > >
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