[Gmsh] FW: from hexahedrons to tetrahedrons

[Smith, Mark]

I think 5 tets in a cube see attached.
mark

-----Original Message-----
From: gmsh-bounces at ace20.montefiore.ulg.ac.be [mailto:gmsh-bounces at ace20.montefiore.ulg.ac.be] On Behalf Of Geordie McBain
Sent: 20 May 2011 03:05
To: Michel Dupront
Cc: gmsh at geuz.org
Subject: Re: [Gmsh] from hexahedrons to tetrahedrons

> I have a structured mesh with hexahedrons and I would like to split 
> each hexahedrons into tetrahedrons.
> Is it possible ?

Hello.  Someone asked me this the other day.  At first I thought it should be easy, but then I found I didn't know how to do it, in Gmsh or otherwise.  I had thought that one should be able to simply split each hexahedron, but then reading the documentation for how it's done in the VTK library:

  http://www.vtk.org/doc/nightly/html/classvtkDataSetTriangleFilter.html

I saw that one must meet `the issue of face compatibility across quadrilateral faces (which way to orient the diagonal?)'.

I figure then that it should be possible to export a hexahedral mesh as VTK, use this VTK function to split to tetrahedra and save as VTK, then reread the VTK.  I haven't actually gone on to try this.

I would be interested to hear of a pure Gmsh solution, if anyone has one.

> if yes into how many tetrahedrons ?

I think the answer for this should be six, since the volume of a tetrahedron with three mutually perpendicular edges of unit length is 1/6.

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