[Gmsh] Reversed orientation of 3rd and 4th order line elements

Christophe Geuzaine cgeuzaine at ulg.ac.be
Wed Mar 18 13:17:58 CET 2015

> On 18 Mar 2015, at 12:43, Schmid, Verena <schmid.verena at siemens.com> wrote:
> Hello,
> I use gmsh version 2.9.0 and came across some unexpected behavior:
> Attached are two example .geo files for a simple geometry with two parts: a square on the left and a square on the right hand side, sharing one edge. I want the boundary of both squares to be oriented counter clockwise. Thus, the shared edge has to be reversed for one square (the one on the right hand side in the example). Based on the manual, this is done adding a minus sign in the  “Physical Line” command. This works fine for linear and quadratic meshes. But when I look at 3rd or 4th order meshes, I have the problem, that the interior edge nodes are not reversed. For the example.msh and the example_reversed.msh I get the following node ordering of line element 3:
> 3rd order: 2,3,9,10 gets reversed to 3,2,9,10
> 4th order: 2,3,10,11,12 gets reversed to 3,2,10,11,12
> Instead, I expected the inner edge nodes to be reversed as well, such that
> 3rd order: 2,3,9,10  would get reversed to 3,2,10,9
> 4th order: 2,3,10,11,12 would get reversed to 3,2,12,11,10                  
> Is this a bug?

Indeed, good catch: the MLineN::reverse() function was not coded. This is fixed in SVN r20639.


> If not, is there a way to obtain the behavior I expected?
> Thank you for your help!
> Kind regards,
> Verena
> <example.geo><example_reversed.geo>_______________________________________________
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Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 

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