dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

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,

Garth

> --
> Anders
>
>
>> Garth
>>
>> >
>> > Johan
>> >
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