[Gmsh] Skipping surface on conversion from STEP to geo_unrolled

Gavin Ridley gavin.keith.ridley at gmail.com
Wed Apr 3 21:53:27 CEST 2019

Hi Dr. Geuzaine,

Thanks for your response. I see the problem here now. It doesn't work after
meshing, although the geometry seems to load to the GUI. Unfortunately, I
need to split a surface into two surfaces, and it seems there's no way to
do that to the STEP file using what's available under the OpenCASCADE
kernel right now. I was hoping to be able to convert the STEP to gmsh-style
geometry, then delete a surface (and its dependent volumes) and replace it
with a new, split one. I'll just have to change the CAD then re-export, I

Thanks again!

On Wed, Apr 3, 2019 at 3:11 PM Christophe Geuzaine <cgeuzaine at uliege.be>

> > On 3 Apr 2019, at 18:23, Gavin Ridley <gavin.keith.ridley at gmail.com>
> wrote:
> >
> > Hi,
> >
> > I would just like to note something to the developers regarding a
> perhaps unnecessary skipping of surfaces in the code.
> >
> > I recently have had to convert a STEP file with fairly complicated
> geometry to a GEO.
> Don't do that. By design, Gmsh never translates from one CAD format to
> another. The "unrolled GEO" feature is there for unrolling complex GEO
> scripts. It can indeed export a limited subset of geometrical entities
> created by other CAD kernels, but it's there only for debugging.
> If you want to modify a STEP model, set
> SetFactory("OpenCASCADE");
> at the beginning of your script. Since we import STEP models with
> OpenCASCADE, this will allow you to modify the file directly with
> OpenCASCADE. See
> https://gitlab.onelab.info/gmsh/gmsh/blob/master/demos/boolean/import.geo
> for an example.
> Christophe
> > This is done so that I can split one of the surfaces in the STEP file to
> set different BCs on different parts of the surface. At the moment, it
> appears that gmsh will skip several surfaces in the conversion from STEP to
> geo_unrolled unnecessarily: surfaces were left out from the gmsh file. A
> warning message comes with this.
> >
> > It seems, however, that the skipped surfaces work fine if you just go
> back in and add surfaces manually. Gmsh now reads the geo file correctly.
> >
> > So, why are these surfaces being skipped? Is there some ambiguity about
> their interpretation from STEP? It would be nice to not have to manually go
> in and add the surfaces.
> >
> > --
> > Thanks,
> > Gavin Ridley
> > _______________________________________________
> > 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

Gavin Ridley
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