[Gmsh] Avoiding duplicate surfaces with OpenCASCADE kernel

[Ingraham, Daniel J. (GRC-LTV0)]

Hi Gmsh users,

I'm trying to mesh a geometry that has some rotational symmetry. In the
past, I've used the Rotate command to help with this, with good results.
With the built-in geometry kernel, everything works fine. With the
OpenCASCADE kernel, however, Gmsh appears to duplicate surfaces when I
define a new elementary volume after rotating the surfaces.

I've read on this mailing list that OpenCASCADE will duplicate surfaces
when they aren't oriented properly, and that this can be disabled if
`Geometry.OCCAutoFix` is set to `0`. I've tried that, but the duplicate
surfaces are still created.

With the built-in kernel, the orientation of a surface can be reversed
by negating its ID number in the `Surface Loop` call, but that doesn't
appear to be the case when using the OpenCASCADE kernel.

I've attached two example geo scripts that demonstrate the problem.
`builtin.geo` uses the built-in kernel, and `opencascade.geo` uses
OpenCASCADE.

Any ideas?

Thanks!

Daniel

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