[Gmsh] How to swith surface normal of a step file and to export this orientation in .mesh format

[NENNIG Benoit]

Dear gmsh team,

I would like to switch orientation of surfaces coming from a part design by FreeCAD and export in step format.
- I try to reverse normal orientation in the FreeCAD (MyShape.reverse() ??) but in gmsh nothing change (however I am not sure of how is made the export in step and if step can store inward normal vector....)
- I try the "classical" gmsh version :
    Physical Surface (1) = {-SufList[]}; 
It works for .msh format (native gmsh) but in .mesh (inria format) only the label is change into -label but the orientation remain the same...
- flip all mesh normal is not possible because I have other shape in my mesh, not concerned with this problem.

Do you have an idea ?

Thanks!

Benoit

ps : In .msh format, I observe that if the surface has strong variation close a small inner corner, the element orientation may be random close to the inner corner if there is only one element on the corner thickness.