[Gmsh] How are set up U and V vectors for elements ?
Christophe Geuzaine
cgeuzaine at uliege.be
Tue Oct 6 19:43:33 CEST 2020
> On 5 Oct 2020, at 07:05, bilou at netc.it wrote:
>
> Hello. I'm trying to parse a mesh.msh generated by gmsh.
>
> I work with 9-quad elements. I see in documentation that inside of the elements, nodes are ordered like this :
>
> v
> ^
> |
> 3-------6-------2
> | | |
> | | |
> 7 8-------5 --> u
> | |
> | |
> 0-------4-------1
>
> I made a 2D mesh (all surfaces normals are oriented in the same direction)
>
> When i look at my 2D mesh (in plan XY) the element 265 :
> 265 2 44 1047 533 49 1102 1103 544 1104
>
> is oriented like this related to the golbal X and Y axis
>
> ie, when looking at the screen i see:
> 44-------49-------2
> | | | Y
> | | | ^
> 1102 1104 544 |
> | | | |
> | | | |
> 1047--1103----533 x------> X
>
> it seems that u anv v vectors are oriented like this :
> 1-----4-----0
> | | |
> | | |
> u <---5-----8 7
> | | |
> | | |
> 2-----6-----3
> |
> V
> v
>
>
> How are V and U vectors defined for each element ?
It depends on the definition of the surface and the meshing algorithm.
> Is there a way to orient them along the natural X and Y axis ?
With the transfinite algorithm you could force the elements to be generated in a certain order by specifying the interpolation corners. But in general you won't know the correspondance - Gmsh produces unstructured meshes! So you would use the (u,v,w) -> (x,y,z) mapping (through e.g. Lagrange basis functions) to make the connection.
Christophe
>
> Thanks
>
>
>
>
> _______________________________________________
> gmsh mailing list
> gmsh at onelab.info
> http://onelab.info/mailman/listinfo/gmsh
—
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine
More information about the gmsh
mailing list