[Gmsh] Units for STEP files

[Victor Kemp]

Thanks Christophe for clearing that up.


On Sun, Mar 31, 2019 at 10:49 AM Christophe Geuzaine <cgeuzaine at uliege.be>
wrote:

>
>
> > On 30 Mar 2019, at 21:32, Victor Kemp <victorkemp at gmail.com> wrote:
> >
> > Thanks Jeremy and Christophe.
> >
> > I think the manual might be wrong in saying that the default "" uses the
> units from the file. I have a file with meters and inches but GMSH 4.2.2
> produces a mesh in millimeters. It also doesn't make sense to use the units
> from the file because there can be more than one, and they're decided
> arbitrarily by the software that created the file and not easily visible to
> the user. Does the default value of Geometry.OCCTargetUnit really mean that
> it uses OCCT's default, which is mm, and behaves the same as Gmsh 3?
>
> When "Geometry.OCCTargetUnit" is empty we don't specify any units, so
> indeed we use OCCT's default behavior, so exactly as in Gmsh 3. I have
> updated the documentation to clarify this. Thanks!
>
> >
> > Also, is it unsafe to use "M" because of those bugs, or have they been
> fixed?
> >
>
> We've still experienced quite a few problems with "M" - which prompted the
> change in the default value for the option in 4.2.
>
> Cheers,
>
> Christophe
>
>
> > I mean 3.0.7, not 3.8.
> >
> >
> > On Sun, Mar 31, 2019 at 2:21 AM Christophe Geuzaine <cgeuzaine at uliege.be>
> wrote:
> >
> >
> >
> > > On 30 Mar 2019, at 08:22, Victor Kemp <victorkemp at gmail.com> wrote:
> > >
> > > How does Gmsh decide what units to use for its dimensionless mesh made
> from a STEP file? I've noticed that different versions seem to do it
> differently. Is there a setting to control this or likely future stability?
> It seems to change unpredictably with each new version and that makes
> interoperability with other software difficult.
> > >
> > > Version 3.early: millimeter
> > > Version 3.8: meter
> >
> > Gmsh 2 and 3 used the coordinates in STEP files as-is, i.e. didn't
> handle units at all. (Note that Gmsh 3.8 does not exist.)
> >
> > > Version 4.0: meter
> > > Version 4.1: meter
> >
> > Gmsh 4 introduced a mechanism to choose the unit, through the
> "Geometry.OCCTargetUnit" option, as mentioned by Jeremy.
> >
> > The default value for that option was "M" (meters) in Gmsh 4.0 and Gmsh
> 4.1. This however led to several regressions, as the conversion for files
> written in other units (millimeters, inches, etc.) would sometimes lead to
> subtle artefacts in the geometry.
> >
> > > Version 4.2: millimeter
> > >
> >
> > So in Gmsh 4.2, the default value of "Geometry.OCCTargetUnit" has been
> set to "" (i.e. empty). This means that we don't translate units by
> default; but you can set the option to your preferred unit if you want to.
> >
> > Christophe
> >
> >
> > >
> > > _______________________________________________
> > > 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
> >
> >
> >
>
> —
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
>
>
>
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