dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, Mar 16, 2012 at 10:27:58AM +0000, Garth N. Wells wrote:
> On 16 March 2012 10:11, Anders Logg <logg@xxxxxxxxx> wrote:
> > On Fri, Mar 16, 2012 at 09:28:41AM +0000, Garth N. Wells wrote:
> >> On 16 March 2012 09:17, Johan Hake <hake.dev@xxxxxxxxx> wrote:
> >> > Hello!
> >> >
> >> > I have implemented a new version of UnitSphere based on subdivision of an
> >> > initial octahedral surface mesh and tetrahedralization using the CGAL
> >> > framework.
> >> >
> >> > This is all fine, but CGAL uses alot of time tetrahedralizing the initial
> >> > surface mesh. CGAL is also doing some funny things with the surface mesh.
> >> >
> >> >  1) It subdivide the initial surface mesh, which I want to prevent. Is
> >> >     that possible.
> >> >  2) 1) results in small triangles on the surface, but large triangles
> >> >     in the interior. I set a tentative volume constraint based on the
> >> >     size of a triangle of the input mesh.
> >> >
> >> > You can try it out here:
> >> >
> >> >  bzr branch lp:~dolfin-core/dolfin/hake-trunk
> >> >
> >> >  from dolfin import *
> >> >  mesh = UnitSphereNew(4)
> >> >  # Do not try larger subdivisions than 4, at least for now.
> >> >
> >>
> >> Did you look at the CGAL demo for generating a mesh or a sphere:
> >>
> >>    http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Mesh_3/Chapter_main.html#Subsection_50.3.1
> >>
> >> ? It uses an implicit surface description. I has planning to add
> >> support for meshing geometries from implicit descriptions.
> >
> > We (Johannes, Benjamin and myself) are planning to port the Netgen
> > Python wrappers for CSG (Constructive Solid Geometry) to DOLFIN C++
> > based on CGAL (which will allow boolean operations). Is this the same
> > thing?
> >
>
> No -  the implicit description is like a level set - the surface of an
> object is described by f(x) = 0. The user needs to provide f and
> sphere in which the object lies. One can also provides a tolerance
> (the accepted distance from the true object edge and the mesh
> boundary). This description is good for non-polyhedral domains,

ok, sounds useful.

--
Anders


> Garth
>
> >
> >
> >> Garth
> >>
> >> >
> >> > Johan
> >> >
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