[Gmsh] Geometry from an order 2 surface mesh

[Christophe Geuzaine]

Hi Jerome,

Yes indeed - all our meshing algorithms currently generate 1st order geometrical elements, starting from 1st order geometrical elements on the boundary. The meshes are then "curved" later on. I will add the ability to re-use a given high-order discrete surface input when we curve to our TODO list. But it's not trivial.

Christophe

> On 1 Jun 2018, at 14:56, Jerome Robert <jeromerobert at gmx.com> wrote:
> 
> Hi all,
> 
> I am trying to fill an existing order 2 3D triangular mesh with order 2 tetrahedron. In the result mesh, the order 2 vertices of my input mesh are all moved so they were linearly interpolated. So everything is as if my input mesh was used by gmsh as an order 1 surface.
> 
> Here is my .geo:
> 
> // Various options I tryed with no luck
> //Mesh.SecondOrderExperimental=1;
> //Mesh.ElementOrder = 2;
> //Mesh.SecondOrderLinear = 0;
> //Mesh.Algorithm3D = 1;
> 
> // surf.unv contains only order 2 triangles
> Merge "surf.unv";
> Surface Loop(2) = {1};
> Volume(3) = {2};
> Characteristic Length {3} = 1000;
> 
> Which I run with gmsh 3.0.6:
> 
> $ gmsh -3 my.geo -o my.msh
> 
> My understanding is that my input mesh is converted to order 1 by this SetOrder1 call:
> 
> https://gitlab.onelab.info/gmsh/gmsh/blob/a4306e50a3916dd52f72edce56c05f36954f3f0a/Mesh/Generator.cpp#L979
> 
> Interpolation on GEntity::DiscreteSurface or GEntity::DiscreteCurve is also always linear.
> 
> So there seems to be no way to use an order 2 mesh as a gmsh GModel. 
> 
> Is that correct ? If not what would be the way to do it ?
> 
> Regards,
> 
> Jerome
> 
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— 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine

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