SWEENT ( swept, path, latrls, extent, nlatrl, state, ifail )
============================================================

  Sweep entity

Receives:
  KI_tag_list_topology     *swept          --- body, vertex, face or list of
                                           --- faces to sweep
  KI_vec_displacement       path           --- translation vector

Returns:
  KI_tag_list_topology     *latrls         --- lateral edge or face(s)
  KI_tag_list_topology     *extent         --- extruded vertex or edge(s)
  KI_int_nitems            *nlatrl         --- number of laterals
  KI_cod_rtlo              *state          --- state of body after sweep
                                           ---   RTLOOK => Valid
                                           ---   RTLONG => Negated
                                           ---   RTLOSX => Self-intersecting
  KI_cod_error             *ifail          --- failure code

Specific errors:
  KI_su_self_intersect      Sweep would produce a self-intersecting surface
  KI_impossible_sweep       Cannot determine swept geometry
  KI_non_manifold           Cannot sweep body with non-manifold boundary
  KI_unsuitable_entity      Body unsuitable for sweep
  KI_wrong_entity           Sweep entity is not a body, vertex or face

Description:
  The entity to be swept is moved along the path vector leaving lateral
  entities in its wake. Entities which may be swept, the laterals they produce
  and the type of the resulting body are identified in the following table.

      Swept Entities        |    Laterals Returned     |      Result
  ===========================================================================
  Minimal body              |   One edge               |     Wire body
                            |                          |
  End vertex of wire body   |   One edge               |     Wire body
                            |                          |
  Wire body                 |   One or more faces      |     Sheet body
                            |                          |
  Sheet body                |   One or more faces      |     Solid body
                            |                          |
  One or more faces of a    |   One or more faces      |     Solid body
  solid body                |                          |
                            |                          |
  General body              |   One or more faces      |     General body
                            |       and edges          |
  ===========================================================================

  For every entry in 'latrls', there is a corresponding entry in 'extent'. This
  list contains the topological entities extruded to create the lateral entities.
  For every lateral face there is a swept edge from the original body and for
  every lateral edge there is a swept vertex.

   Suitable Sweep Entities:

     . Any minimal body.
     . End vertices (in contradistinction to interior vertices) of wires.
     . Any wire body, either an open or closed loop of edges.
     . Any sheet body whose boundary is manifold.
     . Any group of manifold faces of a solid body. Entire shells must
       not be contained within the list.
     . Any general body with only one region and no edges with more than
       two faces.

  Attempting to sweep an entity which is not one of the above will give rise
  to the ifail KI_unsuitable_entity.

  An entity which has an edge whose attached curve is of the type TYCUIN
  (ie intersection curve), TYCUFG (ie foreign geometry), TYCUSP (ie sp-curve)
  or type TYCUCP (ie constant parameter curve) cannot be swept. However tolerant
  edges and sheet bodies, which have curves of type TYCUSP (ie sp-curves)
  attached to their fins can be swept.

  After a sweep any coincident topology will not be fused or united.

  In general this procedure may give rise to self-intersecting body
  boundaries, which could cause unpredictable errors later.


  Any new surfaces created are analytic surfaces if possible. If it is
  not possible to use an analytic surface then the type of the new
  surface will depend on SLIPGS (see SEINTP and OUINTP). If the creation
  of generated surfaces is off, then any new non-analytic surfaces will
  be B-surfaces; if it is on, then they will be swept surfaces.


  If local checking is on, (see SEINTP and OUINTP) consistency checks will be
  made on newly created topological and geometrical entities, and the state
  of the body returned. A state of RTLOOK indicates the body is valid. A state
  of RTLONG indicates that the result body was originally "inside out" but has
  been negated, and is now "positive" (has positive volume) and valid. A state
  of RTLOSX indicates the body is self-intersecting and further modelling
  operations on it may fail.

  If the session parameter for local checking is switched off, the state
  returned will be RTLOOK regardless.

  A self-intersecting body can be returned even if the ifail is zero.

  For general bodies, the body is copied, the copy is transformed,
  corresponding vertices on the body and its copy are joined with
  lateral edges, and corresponding edges are joined with lateral faces.
  All the lateral entities are returned, both edges and faces.  The
  state of RTLONG is never returned since this has no meaning for
  general bodies.