PK_ERROR_code_t            PK_BODY_thicken_2
(
--- received arguments ---
PK_BODY_t                  body,            --- body to be thickened
double                     front_default,   --- default front offset
double                     back_default,    --- default back offset
double                     tolerance,       --- tolerance
const PK_BODY_thicken_o_t *options,         --- options

--- returned arguments ---
PK_TOPOL_track_r_t  *const tracking,        --- tracking information
PK_BODY_thicken_r_t *const results          --- status information
)


Thickens a sheet body into a solid

NOTE: This function supersedes PK_BODY_thicken, which is now obsolete.


Specific Errors:
    PK_ERROR_cant_thicken          thickening failure
    PK_ERROR_bad_tolerance         proposed edge tolerance is too small
    PK_ERROR_not_sheet             body is not a sheet body
    PK_ERROR_bad_thickness         total thickness is zero
    PK_ERROR_inconsistent_offset   the front (or the back ) offsets have
                                   inconsistent sign
    PK_ERROR_inconsistent_thicken  the thicken sense is inconsistent
    PK_ERROR_not_a_unit_vector     the thicken method is
                                   PK_thicken_method_punch_c and the
                                   punch direction is not an unit vector



Introduction
The sheet body is thickened by front_default outwards (i.e. in the
direction of the face normal) and back_default inwards. Exceptional
faces, which have offsets other that the default, are given in the
option structure together with their front and back offset.

The sense of the thicken for a given face, is the sign of the sum of
the front and back offsets of that face. It is an error for this
sense to vary with face.

It is an error if the sign of the front offset varies with
face. Similarly it is an error if the sign of the back offset varies
with face

It is an error if there is a face with front and back offsets such that the
the thickness produced is within RES_linear of zero.

Only manifold sheet bodies can be thickened.

Some edge geometry on the sheet boundary may have to be approximated by
SP-curves in order to generate a boundary curve on the offset faces. If this
is necessary, such edges will have a tolerance less than or equal to the
tolerance supplied through the tolerance argument.

Two situations can give rise to changes in the topology :

    1) Dealing with geometry which fails to offset. If it is known that the
       offset surface of a face would be self-intersecting an attempt is made
       to remove the face. For example, a blend may be removed from an edge.
       The investigation of self-intersection is not exhaustive, however,
       and it can occur that instances are not trapped.

    2) Dealing with configurations which can be repaired. For instance an
       edge may offset to a point or a face become absorbed into the body.


Checking options
The extent to which checking is applied to the body is specified by
the check_fa_fa field of the option structure. At present
check_fa_fa field can only be used to turn on or off face-face
checking, by setting it to PK_check_fa_fa_yes_c or PK_check_fa_fa_no_c
respectively.  If face-face checking is turned on, then face-face
checks are done on the body in addition to default checks.  For most
applications face-face checking will be tuned off, which will give an
adequate level of checking.

Thickening which would lead to a self-intersecting or non-manifold
solid is not allowed. Some of these cases will not be detected when
face-face checking is switched off. In this case the resulting body
will be invalid.

Table of exact cases
Boundary edges with the following curves on these surfaces will be treated
exactly :

    Surface           | Curve
    -----------------------------------------
    Plane             | Line, Circle, Ellipse or B-curve
    Cylinder          | Line, Circle or B-curve equivalent
    Cone              | Line, Circle or B-curve equivalent
    Sphere            | Circle
    Torus             | Circle
    Swept Surface or  | Line, Profile curve or B-curve equivalent
    B-surface equiv   |
    Spun Surface or   | Circle, Profile curve or B-curve equivalent
    B-surface equiv   |


Cases handled
Thickening only handles the cases where each vertex on the boundary of the
sheet meets one of the following requirements.  Either the vertex is smooth
(surface normals constant on all adjoining faces) or both adjoining boundary
edges must have curves of the types treated exactly (see table above) or the
thickening is into the angle of the edge (i.e. convex edges inwards only and
concave edges outwards only).


Tracking Information
The function returns tracking information relating to which topology
was split, deleted and created. For more information regarding
these structures, please refer to the PK documentation for the
PK_TOPOL_track_r_t structure.

Returned Status and Error Information
If this function returns a value of PK_ERROR_no_errors, the result of
the "thicken" operation will be indicated by the value of the
status field within the results structure.

There are two values for the status field which can indicate a
successful operation :

 o PK_local_status_ok_c      : Indicates that the operation was successful
                               and the modified body is valid.

 o PK_local_status_nocheck_c : Indicates that the operation was successful,
                               but the check_fa_fa field in the option
                               structure was set to PK_check_fa_fa_no_c.

The remaining `PK_local_status_...' codes indicate some failure. The failure
code is normally accompanied by an array of entities which indicate where
the failure or problem occurs. For more information regarding these failure
codes and the returned error entities, please refer to the PK documentation
for the PK_BODY_thicken_r_t structure.