PK_ERROR_code_t                   PK_FACE_intersect_face
(
--- received arguments ---
PK_FACE_t                         face_1,     --- first face
PK_FACE_t                         face_2,     --- second face
const PK_FACE_intersect_face_o_t *options,    --- options structure

--- returned arguments ---
int                        *const n_vectors,  --- number of point intersections
PK_VECTOR_t               **const vectors,    --- posns of point intersections
int                        *const n_curves,   --- number of intersection curves
PK_CURVE_t                **const curves,     --- intersection curves
PK_INTERVAL_t             **const bounds,     --- bounds of curves
PK_intersect_curve_t      **const types       --- types of intersections
)


PK_FACE_intersect_face finds the intersections between two faces.


Specific Errors:
    PK_ERROR_missing_geom              face has no attached geometry
    PK_ERROR_bad_option_data           bad option structure data given
    PK_ERROR_not_on_curve              given parameters not on curve
    PK_ERROR_cant_do_intersect         intersection cannot be done



 PK_FACE_intersect_face finds the intersections between two faces
 (face_1 and face_2), returning intersection points (vectors)
 and curves of intersection (curves).

 If the faces are from the same body any curves returned will be created as
 construction geometry in the body.

 If the faces are from different bodies and any of the curves returned are of
 type intersection curve, then these curves will refer to copies of
 the surfaces of faces.

 No attempt is made to define surface regions of partial coincidence, and
 if the surfaces of faces are fully coincident no intersection data will be
 returned.

 The returned points (vectors) will be returned at points where the faces
 make point contact. n_vectors indicates the number of intersection points.

 The curves returned (curves) will be the basis curves of trimmed curves,
 and their corresponding bound in bounds,  n_curves indicates
 the number of curves returned.

 type classifies curves as being either:

      PK_intersect_curve_simple_c : Simple intersection curves
   or PK_intersect_curve_tangent_c: Tangent intersection curves


 The available fields in the option structure PK_FACE_intersect_face_o_t are as
 described below:

 The option have_box indicates whether a box has been specified
 (default = PK_LOGICAL_false)

 The option box enables a 3-space box of interest to be supplied. The
 box may be used to improve performance. The intersection curves returned
 are not guaranteed to lie within the bounds of the box.

 The option have_uvbox_1 indicates whether a uvbox_1 has been specified.
 The option have_uvbox_2 indicates whether a uvbox_2 has been specified.

 The options uvbox_1 and uvbox_2 enable the supplying of parameter boxes
 for the first and second face respectively. Again these
 boxes are only used to constrain the region of interest for performance
 purposes. The intersection curves returned are not trimmed to lie
 within the boundaries of the parameter box/es.
 Four parameters should be supplied to define the parameter box, U-min,
 U-max, V-min and V-max.

 The option have_vector indicates whether a uvbox_2 has been specified.

 The option vector enables a point on a branch of the intersection to be
 specified (by supplying the x, y, and z coordinates). For this
 case only the branch of the intersection on which this point lies will be
 returned.