Function face_directions 

pub fn face_directions(
    mesh: &Triangulation,
    options: &Directions,
    tol: Tolerances,
) -> OgeomResult<Vec<FaceDirection>>

The directions a mesh’s flat faces face, largest area first.

See the module documentation for what is reported. A direction and its antipode are one face direction. An empty mesh, or one whose triangles all have no area, has none.

Errors

OgeomError::Domain for options out of range, or a triangle indexing a vertex the mesh does not have.