CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

It is not guarantee that the convex hull of the original mesh will be
preserved in a Delaunay or Regular triangulation after adding the
new nodes. I don't see an easy solution to this problem without using
a conforming triangulation (and even with, you might get some Steiner
points on your constrained facets).

Sebastien.

On 01/27/2014 06:13 PM, Qianqian Fang wrote:
> On 01/27/2014 02:00 AM, Sebastien Loriot (GeometryFactory) wrote:
> > Could you give some details on the distribution of new nodes
> > and how you would like them to be connected to the surface?
>
> hi Sabastien
>
> for a convex shaped mesh, my goal is actually make a new
> convex hull including the new nodes, and fill the extended
> space with new (delaunay) tetrahedra (the original mesh
> space is not changed).
>
> An example is to add a node over the top facet of a cube-like mesh:
> the resulting mesh will be a pyramid-over-cube (see attachment):
> the bottom cube is the same as the original, the top pyramid is
> filled by tetrahedra, each has a base on one of the surface triangles
> on the top cube surface, and a tip at the newly added node. If two
> nodes are added over the top facet, I expect to see a
> "tent-over-cube" mesh, etc ...
>
> For a mesh with cavities, I'd like to again get the convex hull
> covering both the old nodes and the new nodes first, and tessellate
> the extended space (without refining for quality purposes), and
> then remove the new elements that do not share the newly
> inserted nodes.
>
> let me know if I can explain this better.
>
> Qianqian
>
> > I don't think you will be able to do something like this using
> > something out-of-the-box.
> >
> > Sebastien.
> >
> > On 01/27/2014 12:29 AM, Qianqian Fang wrote:
> > > Dear list:
> > >
> > > for a project of mine, I need to modify a pre-made
> > > tetrahedral mesh (output of CGAL 3D mesh generator)
> > > by adding a bunch of additional 3D nodes. The new nodes
> > > are outside of the existing mesh. I'd like to insert new
> > > tetrahedra between the new nodes and the surface triangles
> > > that have direct sight to the new nodes. It is important not
> > > to insert any additional nodes aside from the ones I need.
> > > The quality of the new elements are not important
> > > and thus a quality-based refinement is not preferred.
> > >
> > > I am wondering if anyone know if this is possible in
> > > CGAL? it would be wonderful if you can point me to
> > > the CGAL sample or share a code snippet to illustrate
> > > how to implement.
> > >
> > > thank you very much
> > >
> > > Qianqian