[Dune] DGF format and local ordering of vertices

[Dedner, Andreas]

I'm afraid there is no guarantee. This has nothing directly to do with dgf but with the general
structure of the dune grid interface. A grid manager could require a specific orientation - so I think
alu originally required triangles to be oriented counter clock wise (but alu was originally only for
the flat case); another grid manager could require clock wise
The documentation for dgf is merely stating that you do not need to know what the grid manager requires
but can use any orientation.
That also means that the question if orientation is preserved must depend on the grid manager used.
Afaik alugrid and alberta will preserve the orientation you use in the dgf file - as grids supporting surface
clockwise or counter clockwise does not really make a lot of sense any more...
Andreas



________________________________
From: dune-bounces+a.s.dedner=warwick.ac.uk at dune-project.org [dune-bounces+a.s.dedner=warwick.ac.uk at dune-project.org] on behalf of Sacconi, Andrea [a.sacconi11 at imperial.ac.uk]
Sent: 27 September 2012 17:10
To: dune at dune-project.org
Subject: [Dune] DGF format and local ordering of vertices

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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