struct PK_BODY_thicken_o_s
    {
    int                       o_t_version;   --- version number
    int                       n_faces;       --- number of non-default faces
                                             --- (0)
    const int                *faces;         --- faces without default offsets
                                             --- (NULL)
    const double             *front_offsets; --- front offsets
                                             --- (NULL)
    const double             *back_offsets;  --- back offsets
                                             --- (NULL)
    PK_check_fa_fa_t          check_fa_fa;   --- check for face-face
                                             --- (PK_check_fa_fa_yes_c)
    PK_thicken_method_t       method;        --- thickening method
                                             --- (PK_thicken_method_offset_c )
    PK_VECTOR1_t              punch_dir;     --- punch direction
                                             --- (zero vector)
    PK_offset_method_t        offset_method; --- offset method
                                             --- (PK_offset_method_accurate_c )
    };

typedef struct PK_BODY_thicken_o_s PK_BODY_thicken_o_t;



This option structure allows individual faces to be given offsets different
from the defaults, and controls what checking is performed.


Description of fields:

n_faces           Length of faces, front_offsets and `back_offsets
                    arrays.

faces             Array of length n_faces, containing faces with
                    non-default offsets.

front_offsets     Array of length n_faces, of front offsets in
                    correspondence to the face array.

back_offsets      Array of length n_faces, of back offsets in
                    correspondence to the faces array.

check_fa_fa       Check for face-face inconsistencies. Permitted values
                    are:
                        PK_check_fa_fa_yes_c
                        PK_check_fa_fa_no_c

method            Thickening method. Permitted values are:
                        PK_thicken_method_offset_c: The side surfaces are
                        created by ruling the side edges along the
                        direction of the surfaces normals.
                        PK_thicken_method_punch_c: The side surfaces are
                        created by sweeping the side edges along an user
                        supplied punch direction.
                    The default value is: PK_thicken_method_offset_c.

punch_dir         Vector of the punch direction. This must be set if
                    'method' is PK_thicken_method_punch_c, and otherwise is
                    ignored.
                    The default value is a zero vector.

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