PICKEN ( palist, transf, point, axis, rad, opt, entype, nhiten, hitlis, 
========================================================================
         indlis, dislis, hitpts, ifail )
         ===============================

  Pick entities inside a cylindrical volume.

Receives:
  KI_tag_list_part         *palist         --- part or list of parts
 <KI_tag_list_<transform>> *transf         --- transformation or
                                           --- list of transformations
  KI_vec                    point          --- point through which axis passes
  KI_vec_direction          axis           --- axis of cylindrical volume
  KI_dbl_radius            *rad            --- radius of cylindrical volume
  KI_cod_slpk              *opt            --- ray options
  KI_cod_ty                *entype         --- type of entity to pick

Returns:
 <KI_int_nitems>           *nhiten         --- number of picked entities
 <KI_tag_list_entity>      *hitlis         --- list of picked entities
 <KI_tag_list_int>         *indlis         --- list of indices of the
                                           --- owning parts
 <KI_tag_list_dbl>         *dislis         --- list of minimum distances
                                           --- from picked entities to ray
 <KI_tag_list_dbl>         *hitpts         --- points on ray axis
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_bad_type               check ray type is correct
                            entity in part list is of incorrect type
  KI_wrong_transf           unsuitable transform
  KI_wrong_entity_in_list   entity in part list is of incorrect type
  KI_not_same_length        part and transform lists are of different lengths

Description:
  PICKEN provides assistance in selecting entities from a display.  PICKEN fires
  a thick ray at a list of parts and can return any edge, vertex, construction
  curve or construction point hit. The inverse of a transform in 'transf' is
  applied to the ray before it is fired at the corresponding part in 'entys';
  i.e. PICKEN acts as if each part in 'entys' is transformed (by the
  corresponding transform in 'transf') before firing the ray, without actually
  transforming them.

  If none of the parts are to be transformed, 'transf' may be specified as a
  null tag. A null tag in 'transf' is interpreted as the identity
  transformation.

  The volume from which the entities will be picked is defined as a cylinder of
  infinite length. The axis of the cylinder passes through 'point' and runs
  parallel to 'axis'. The radius of the cylinder is 'rad'.

  'entype' is the type code which determines what type of entity to look for.
  If a body or list of bodies is given, vertices, edges, construction points and
  construction curves can be found, so either TYTOVX, TYTOED, TYGEPT or TYGECU
  can be given. If an assembly or list of assemblies is given, only construction
  points and construction curves can be found, so either TYGEPT or TYGECU can be
  given.

  'opts' is the type code which determines whether the ray is to be infinite
  SLPKIR or semi_infinite SLPKSR. If SLPKIR is selected then PICKEN will return
  all entities along the whole ray. If SLPKSR is selected then PICKEN will
  return entities along a ray starting at 'point' and in the direction 'axis'.

  All the entities of the correct type which lie within the defined region will
  be found. The data will be returned in three lists of length 'nhiten' as
  follows:

      'hitlis' - A list of tags of picked entities
      'indlis' - A list of indices of the owning bodies or assemblies
      'dislis' - A list of minimum distances from picked entity
                 to the defined axis
      'hitpts' - A list of points on the axis corresponding to the
                 minimum distances in 'dislis'.  These points are the
                 projections of the minimum distance points on to the axis.

  The entries in the lists will be sorted according to the values in the
  'dislis' list, so that the nearest entity comes first.

  If no suitable entities are found, the value of 'nhiten' will be zero and
  'hitlis', 'indlis', 'dislis' and 'hitpts' will be returned as the null tag.

  The distances are not determined to modelling accuracy, and so this routine
  should only be used for operations such as picking from a display, and not for
  modelling calculations.

  If transforms are supplied they may only contain translation and rotation
  components. Reflections, scales and shears are not allowed.