[Gmsh] (again) on v4 mesh format

[Christophe Geuzaine]

> On 6 Sep 2018, at 15:04, Alessandro Vicini <alessandro.vicini at sitael.com> wrote:
> 
>  
> In version v2 of the mesh file, surface elements are directly associated to the physical ID of the surface they belong to (which is useful).
> If I get it right, in version v4 this direct association is missing: the surface elements are associated with the elementary ID of the surface, and the correspondence between elementary and physical surfaces is to be found in the Entities list.

Exact.

> My question is: is it possible with version v4 to still have the direct association surface element -> physical surface? Thank you.

As you mentioned, you have it through the "Entity" definitions. The handling of physical groups in version 2 had numerous issues (see https://gitlab.onelab.info/gmsh/gmsh/issues/94). Two of the most serious were that

- if you defined more than 1 group for a given geometrical entity, the elements would be duplicated
- storing the physical group for each element was wasteful (as many integers as elements, instead of a single one)

Christophe

PS: note that if you liked the version 2 format, you can continue to use it (just set Mesh.MshFileVersion=2.2; in your geo file or in your default options) - we will continue to support it. (We still support Version 1...)



> Alessandro
>  
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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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