struct PK_BODY_hollow_o_s
    {
    int                o_t_version;    --- version number of option structure
    int                n_pierce_faces; --- number of faces in pierce_faces
    const PK_FACE_t   *pierce_faces;   --- faces to be pierced (not offset)
    PK_check_fa_fa_t   check_fa_fa;    --- check for face-face inconsistencies
                                       --- (PK_check_fa_fa_yes_c)
    int                n_offset_faces; --- number of elements in offset_faces
                                       --- and offset_values (0)
    const PK_FACE_t   *offset_faces;   --- faces to be offset by a different
                                       --- value than the function value (NULL)
    const double      *offset_values;  --- offset values for corresponding
                                       --- faces in offset_faces array (NULL)
    PK_LOGICAL_t       pierce_tangent; --- process tangent pierce faces before
                                       --- hollowing operation
                                       --- (PK_LOGICAL_false)
    PK_offset_method_t offset_method;  --- offset method
                                       --- (PK_offset_method_accurate_c)
    };
typedef struct PK_BODY_hollow_o_s PK_BODY_hollow_o_t;


This structure contains optional controls for PK_BODY_hollow_2



Description of fields:

n_pierce_faces        Length of pierce_faces array. The default value
                        is 0.

pierce_faces          The array of faces which are not to be offset. Pierced
                        faces remain only as a section through the hollowed
                        body. For instance, hollowing a cylindrical solid with
                        one end face pierced will result in a tube with one
                        open and one closed end. The default value is NULL.

check_fa_fa           Check for face-face inconsistencies. Permitted values
                        are:
                             PK_check_fa_fa_yes_c
                             PK_check_fa_fa_no_c
                        The default value is PK_check_fa_fa_yes_c.

n_offset_faces        Length of offset_faces and offset_values arrays.
                        The default value is 0.

offset_faces          The array of faces which are to be offset by a value
                        different to that specified via the function arguments.
                        Every face in this array must be matched with a
                        corresponding value in the offset_value array.
                        Faces listed in this array must not be listed within
                        the pierce_faces array.
                        The default value is NULL.

offset_values         The array of specific face offset values. Every value
                        in this array is associated with the corresponding
                        face in the offset_faces array.
                        The same rules apply to these offset values as the
                        offset parameter specified in the function argument
                        list. A zero value is allowed: the associated face
                        will be treated as a pierce face.
                        The default value is NULL.

pierce_tangent        A "tangent pierce face" is a pierce face which
                        shares at least one smooth edge with a face which
                        is not a pierce face. When this option is set to
                        PK_LOGICAL_true, any tangent pierce face(s) will be
                        processed before offsetting the faces in the body
                        so that side faces can be created along the smooth
                        boundary edges. Setting this option to
                        PK_LOGICAL_true has no effect on the result if
                        the body has no tangent pierce faces.

offset_method         The method used for offsetting surfaces in the body.
                        The default value is PK_offset_method_accurate_c.