[Gmsh] MeshFormat Version number

[Christophe Geuzaine]

j s wrote:
> My gmsh reader relies on the fact that each physical number is unique 
> across dimensions.  Are you saying this is no longer happening?
>  

Hi Juan - Physical entity ids have *never* been unique across 
dimensions---cf. the documentation. As with elementary entity ids, they 
must be unique per dimension. (You cannot have Nurbs(1) and Spline(1), 
but you can have Point(1) and Spline(1). This is deeply rooted in the 
boundary representation model used by Gmsh.)

Of course, nothing prevents you from *choosing* unique physial ids 
gobally... This was basically what we forced when assigning names 
instead of numerical ids to physicals in the previous version of the 
mesh file. This was an oversight, since it could lead to ambigious cases 
when reading a mesh.



> This is going to be a few hours effort to change my algorithm, so please 
> help me understand all of the ramifications correctly.
>  
> I then need to check the dimensionality of each element I am reading in 
> and assign it to a different group according to number and dimension?  
> Why can't we just use names instead of numbers, and ensure that the 
> names are unique across all dimensionalities?
>  
> Juan
> 
> On Wed, Sep 2, 2009 at 7:59 AM, Christophe Geuzaine <cgeuzaine at ulg.ac.be 
> <mailto:cgeuzaine at ulg.ac.be>> wrote:
> 
>     Geordie McBain wrote:
> 
>         On Mon, Aug 31, 2009 at 11:07 AM, Rui
>         Maciel<rui.maciel at gmail.com <mailto:rui.maciel at gmail.com>> wrote:
> 
>             Does anyone know what changed between the previous and the
>             new file format
>             version?
> 
> 
>         The motivation,according to doc/VERSIONS.txt is `bumped mesh version
>         format to 2.1
>         (small change in the $PhysicalNames section, where the group
>         dimension
>         is now required)'.
> 
> 
>     Exactly: it's a very small change, only affecting the optional
>     $PhysicalNames/$EndPhysicalNames section.
> 
>     The problem was that with version 2, we did not save a dimension
>     (0D, 1D, 2D or 3D) together with the name. Hence we could not
>     guarantee a one-to-one mapping between physical names and physical
>     numbers. Indeed,  physical numbers need only to be unique per
>     dimension (you can have Physical Point(1) and Physical Line(1)).
> 
> 
> 
> 
> 
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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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> 


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine