Function offset_polyhedron 

pub fn offset_polyhedron(
    verts: &[[f64; 3]],
    faces: &[[usize; 3]],
    d: f64,
) -> OffsetMesh

Offset a closed polyhedron mesh outward (or inward for negative d).

Equivalent to OffsetMesh::from_triangle_soup(verts, faces).offset(d) but named for clarity when working with closed polyhedra.