[Dune] DGF format and local ordering of vertices

[Martin Nolte]

As Andreas already pointed out, there is no such guarantee and requiring such a 
thing will break some grid managers (e.g., AlbertaGrid or ALUGrid). Moreover, in 
the case of a hypersurface, the term orientation does not even make sense.

What do you want this information for? If you just want the (covariant) normal, 
you can obtain them from the intersections. If you can come up with a situation 
where a face normal is needed independent of the intersection, let us know.

Best,

Martin

On 09/27/2012 06:10 PM, Sacconi, Andrea wrote:
> Hi everyone,
>
> I'd like to ask you a question about the Dune Grid Format (DGF) and the ordering
> of the corners in an element of the mesh.
>
> Suppose I put my vertices and my simplices in a dgf file, and then I use it to
> feed the grid constructor (Alberta, ALUGRID, whatever).
> In the online documentation about the DGF, under the field "Simplex", I read
> that "no ordering of local vertices is required".
> In my particular case, however, I do need a special ordering, since I'm dealing
> with hypersurfaces. To set an example: if you have the unit cube as initial
> geometry, I need that, looking from outside, all the triangles have corners
> counter-clockwise oriented s.t. the unit normal points outward. I do need that
> this ordering (used in .dgf file) is preserved!
>
> Is there any way of knowing whether this important information is preserved?
> Otherwise, the computation of the normal to each triangle could lead to weird
> results (strong nonsymmetric time-dependent behaviour for initial symmetric
> configurations).
>
> Thanks for your help!
>
> Andrea
> __________________________________________________________
>
> Andrea Sacconi
> PhD student, Applied Mathematics
> AMMP Section, Department of Mathematics, Imperial College London,
> London SW7 2AZ, UK
> a.sacconi11 at imperial.ac.uk
>
>
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-- 
Dr. Martin Nolte <nolte at mathematik.uni-freiburg.de>

Universität Freiburg                                   phone: +49-761-203-5630
Abteilung für angewandte Mathematik                    fax:   +49-761-203-5632
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