[Gmsh] The direction of normal vectors on the surface elements

[Hanzhi Diao]

Hello,

I am struggling with the direction of the normal vectors on the surface
elements in 3D meshing.

I mesh the surface of a closed 3D Lipschitz domain.

I'd like to know whether there is a generalized approach in Gmsh such
that the resulting surface triangles have the uniformly numbered
vertices.  Then, their normal vectors (calculated by cross product) can
point either outwards or inwards w.r.t. the closed 3D domain.

So far, when modelling the simple domain, I can select the lines/curves
deliberately in order to form a clockwise/counterclockewise loop.

I had a look at the manual but have no idea how to do it in Gmsh.  Or,
perhaps it has to be done outside Gmsh as the post-processing?

Thanks in advance.

Best regards,
Hanzhi