dolfin team mailing list archive

[Bartosz Sawicki <sawickib@xxxxxxxxxxxxx>]

Kent Andre wrote:
> On ma., 2009-06-22 at 00:40 -0600, Bartosz Sawicki wrote:
> > On 22/06/09 12:06 AM, Anders Logg wrote:
> > > On Sun, Jun 21, 2009 at 11:36:29PM -0600, Bartosz Sawicki wrote:
> > > > On 19/06/09 02:53 PM, kent-and@xxxxxxxxx wrote:
> > > > > When using VMTK the boundary indicators are stored as a set of arrays
> > > > > with names
> > > > > boundary facet cells,
> > > > > boundary facet numbers
> > > > > boundary indicators
> > > > > The two first arrays are used to find the global facet numbers.
> > > > > The function computes a mesh function based on these arrays.
> > > > >
> > > > > This was what Anders prefered since VMTK does not now anything
> > > > > about the global numbering of facets in Dolfin (without linking it into
> > > > > Dolfin).
> > > > >
> > > > > This is not a VMTK specific problem, but I do think VMTK is the only
> > > > > mesh-generator
> > > > > that let you store boundary indicators at the moment. I guess we should add
> > > > > this to NetGen as well, both Hans Petter Langtangen and Douglas Arnold has
> > > > > bugged
> > > > > me about this the last few days.
> > > > I'm every day user of this functionality. I use Netgen generated models, 
> > > > but also other software which add boundary indicators to existing 
> > > > meshes. Netgen supports boundary indicators quite well, both by geo 
> > > > files, and by GUI. I don't understand what you want to add?
> > > Is it possible to set DOLFIN boundary indicators from Netgen? I didn't
> > > know.
> > It is definitely possible :) I don't have direct converter from Netgen 
> > vol to Dolfin xml. Most of my old models were stored in Diffpack grid 
> > format, so I'm using grid to xml converter.
> > Netgen can export to the grid format, so this is not a big issue.
>
> It is not possible to store the boundary indicators in Dolfin format
> using Netgen, at  the current time. I wrote the Netgen -> dolfin filter
> in Netgen so I should know :).  
>
> But it should be possible to include support for that in a similar
> fashion as we did in VMTK. 

You are right that Netgen doesn't support Dolfin XML mesh format. But it 
doesn't mean that is not possible to use boundary indicators generated 
by Netgen in Dolfin. Converterting via Diffpack grid file preserves 
boundaries.

The algoritm is simple:
1. Generate mesh using Netgen.
2. Mark boundaries indicators.
3. Export to Diffpack format.
4. Convert Diffpack to XML.
5. Enjoy boundary indicators in Dolfin.

cheers,



cheers,
BArtek




> > > Meshing is a problem for us. I don't know what the long-term goal
> > > is. Netgen is good but it would be nice if the interface could be
> > > updated to a modern toolkit instead of Tk.
> > True. Netgen is good mesher, but its development stopped several years 
> > ago. Few months ago Joachim registered sf.net project, so there are 
> > chances for new activity,
> >
> > > One option could be to add meshing capabilities to MeshBuilder (using
> > > an external library like Netgen).
> > This shouldn't be difficult to do. Of cource it depends how strong 
> > integration you need.
> >
> > > I'd like a tool where I can
> > >
> > >   1. draw simple domains in 2D / 3D
> > Simple modeler/CAD ?
> >
> > >   2. import CAD geometry
> > I recommend to use STL as portable format.
> >
> > >   3. set boundary indicators
> > Netgen has such feature.
> >
> > >   4. create and export Mesh in DOLFIN XML
> > Set of converters can solve this problem.
> >
> >
> >
> >
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