CGAL users discussion list

[Sascha Zelzer <>]

Hi,

I don't know. I would have thought that the optimization step is allowed 
to modify the position of the initial seed points. Contrary to 1D 
features for example.

- Sascha

On 10/02/2012 07:35 PM, Hamid G wrote:
> Thanks Sascha, this was a great help.
>
> Do you know if the seeded points are going to be preserved in the mesh
> or they are just temporary guides for the meshing algorithm?
>
>
>
> On Fri, Sep 28, 2012 at 12:15 PM, Sascha Zelzer
> <>
>  wrote:
> > Sure,
> >
> > I have attached a file with my code. You can ignore the types in the "mitk"
> > namespace, or replace them with CGAL types where appropriate.
> >
> > In my case, I have a labelled image as the input for the CGAL mesher for
> > which I can provide a mapping of labels to a sampling distance for the seed
> > points (the SeedPointDistanceToLabelMap type in the attached code). So for
> > example I know that my image contains three labels, with consecutive values
> > from 1 to 3. For value 1 I need a sampling distance of 15mm (for example),
> > for value 2 5mm, etc. I then simply iterate over all different sampling
> > distances and for each distance, I iterate over the whole image (with
> > stepping according to the current distance) and create a seed point if the
> > current image value corresponds to a label value for which that sampling
> > distance is required.
> >
> > The created seed points are then inserted into the triangluation object of
> > my domain (instead of relying on the default constructed seed points in
> > make_mesh_3). I'm not sure if that approach has any disadvantages (apart
> > from brute force iterating over the image) but it seems to work okay.
> >
> > - Sascha
> >
> >
> > On 09/28/2012 05:47 PM, Hamid G wrote:
> > > Sascha,
> > >
> > > Would you mind elaborating on what exactly you did? I have same
> > > problem and using varying sizing field didn't help me either.
> > >
> > > thanks in advance,
> > >
> > > On Mon, Sep 17, 2012 at 3:37 PM, Sascha Zelzer
> > > <>
> > >  wrote:
> > > > Hi,
> > > >
> > > > I was finally able to construct a suitable set of seed points and run the
> > > > mesh generation step successfully.
> > > >
> > > > Many thanks for your hints!
> > > >
> > > > Before my first posting to this list, I have tried using a
> > > > CGAL::SizingField
> > > > and setting different values for the tet radii for the different
> > > > sub-domains. That did obviously not work out and I now know it is because
> > > > of
> > > > an inappropriate default seed point set.
> > > >
> > > > Thanks,
> > > >
> > > > Sascha
> > > >
> > > >
> > > > On 09/10/2012 09:57 AM, Mariette Yvinec wrote:
> > > >
> > > > Currently,
> > > > the best way to ensure that small component are mot missed
> > > > is to set initial points in them or on them boundary.
> > > > Then you have to use refine_mesh_3 instead of
> > > > make_mesh_3 for your initaial seeding points to be taken into account.
> > > >
> > > > Another way, if you know the area where the small components are supposed
> > > > to
> > > > be,
> > > > is to define a  variable sizing field with a value locally similar to the
> > > > size of the components
> > > > to be meshed.
> > > >
> > > >
> > > >
> > > > Le 30/08/12 16:18, Sascha Zelzer a écrit :
> > > >
> > > > Hi,
> > > >
> > > > I have posted about my problem already here
> > > >
> > > > http://cgal-discuss.949826.n4.nabble.com/3D-volume-mesher-ignoring-small-subdomains-td4655756.html
> > > > but thought I reformulate it:
> > > >
> > > > I have a labeled image as input to make_mesh_3 which contains a small
> > > > sub-domain (label 2) inside a larger domain (label 1). Small meaning the
> > > > its
> > > > characteristic size is about two orders of magnitude smaller then the
> > > > embedding domain.
> > > >
> > > > So my question is, what are the criteria for refining cells in the large
> > > > domain to ensure that they do not "shadow" a complete small sub-domain? I
> > > > would like to be able to set a large maximum cell size for the large
> > > > domain
> > > > and a suitable cell size for small sub-domain. When setting the cell and
> > > > facet criteria in such a way, my small sub-domain is ignored however.
> > > >
> > > > Any tips would be highly appreciated.
> > > >
> > > > Thanks,
> > > >
> > > > Sascha
> > > >
> > > >
> > > > --
> > > > Mariette Yvinec
> > > > Geometrica project team
> > > > INRIA  Sophia-Antipolis