Foreign Surface
The foreign surface consists of two perpendicular unit vectors (e1 and e2), the normal to the plane(e3), the origin of the plane and the foreign ID returned by the function user_init_surf().
Data Format:
e1[3] Unit vector, in the u direction
e2[3] Unit vector, in the v direction
e3[3] Normal to the plane
origin[3] Origin of the plane
foreign_id Foreign ID returned by user_init_surf()
Parameterization is established by the Foreign Surface callback function user_eval_surf().