ENPBEN ( entity, ulimit, vlimit, ifail )
========================================

  Calculates the parametric box of the given entity.

Receives:
  KI_tag_topology          *entity         --- entity whose parametric box
                                           --- is required

Returns:
  KI_dbl                    ulimit[2]      --- u parametric limits
  KI_dbl                    vlimit[2]      --- v parametric limits
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_missing_geom           QTP_param_rubber
  KI_no_geometry            entity does not have geometry attached
  KI_wrong_entity           entity is not a face

Description:

  The entity must be a face.

  U and v parametric limits are returned in two arrays. Element
  zero of 'ulimit'  will contain the lower u value and element one
  the upper u. Element zero of 'vlimit' will contain the lower v
  and element one the upper v.

  The u and v limits will bound an area of the surface in which the
  face is defined. The surface parameter space is defined by ENSUPA
  in two arrays 'urange' and 'vrange'. The parameter box is defined

  (1)
                   'ulimit[0]' < 'ulimit[1]'  and
                   'vlimit[0]' < 'vlimit[1]'

  (2)
           'ulimit[1]' - 'ulimit[0]' <= 'urange[1]' - 'urange[0]'
           'vlimit[1]' - 'vlimit[0]' <= 'vrange[1]' - 'vrange[0]'

  Hence for surfaces with periodic parameters the parameter box can
  never be larger than the period of the corresponding surface
  parameter.

  (3)
              'urange[0]' <= 'ulimit[0]' < 'urange[1]'
              'vrange[0]' <= 'vlimit[0]' < 'vrange[1]'

  So for a face that 'straddles' the boundary of a periodic
  parameter, the upper parameter value will be greater than the
  upper parameter range.

  An attempt to find the parametric box of a face with no surface
  attached or insufficient geometry will fail.