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

Schmid, Verena schmid.verena at siemens.com
Wed Mar 18 12:43:43 CET 2015


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? If not, is there a way to obtain the behavior I expected?

Thank you for your help!
Kind regards,
Verena

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