dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Jun 24, 2009 at 09:54:10AM +0200, Kent Andre wrote:
> On ti., 2009-06-23 at 11:09 -0600, Bartosz Sawicki wrote:
> > Kent Andre wrote:
> > > On ma., 2009-06-22 at 20:57 +0200, Anders Logg wrote:
> > >> On Mon, Jun 22, 2009 at 12:46:09PM -0600, Bartosz Sawicki wrote:
> > >>> 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,
> > >> Nice, but not optimal. At some point, we need an application that can
> > >> do all of these (and more). There seem to be a couple of different
> > >> options:
> > >>
> > >>   1. Extend Netgen with full support for DOLFIN (and change the toolkit...) 
> > >>   2. Extend Gmsh with full support for DOLFIN (and change the toolkit...)
> > >>   3. Extend MeshBuilder to do mesh generation (using for example Netgen)
> > >>   4. ?
> > >>
> > >> Any thoughts on these options?
> > >>
> > >> The problem with (3) is that no one is really developing MeshBuilder,
> > >> except when we pay Kalkulo (http://simula.no/applications/kalkulo/) to
> > >> do it.
> > >>
> > > 
> > > It should be fairly easy to include bc indicators in NetGen. I can look
> > > at it, I think I need to update the filter anyway to make sure the mesh
> > > is ordered correctly according to UFC. 
> > 
> > Are you going to extend Netgen to enable export into dolfin-xml?
> > You mentioned about some filter, is it somewhere in dolfin repository? I 
> > can't find anything. Can upload your code into dolfin-convert utility?
> 
> Netgen, in its newest version, can export to dolfin xml. But only the
> mesh, not the bc indicators. 
> 
> > 
> > > In general it is rather easy to write out the mesh and indicators
> > > compared to actually making it. I bet we can make Gmsh write Dolfin mesh
> > > in just a few hours (but I have not looked at Gmsh). 
> > 
> > I'm sure that it will be easy. But don't you thing that good converter 
> > is more flexible solution?
> > 
> > cheers,
> > 
> 
> I don't know. 

Writing directly to DOLFIN from inside Gmsh should be just as flexible
as first writing to Diffpack and then converting. But having a good
conversion tool is also important.

-- 
Anders

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