CRSPTC ( surf, t_cu, tol, degens, sense, nspc, spc, ifail )
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  Approximate a trimmed curve by an SP-curve.

Receives:
  KI_tag_surface           *surf           --- surface upon which 't_cu' lies
  KI_tag_curve             *t_cu           --- trimmed curve to approximate
  double                   *tol            --- required tolerance
  KI_cod_logical           *degens         --- create degenerate SP-Curves
  KI_cod_logical           *sense          --- SP_Curve sense

Returns:
  KI_int_nitems            *nspc           --- number of SP-curves returned
  KI_tag_list_curve        *spc            --- SP-curves
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_failed_to_create_sp    failed to create SP_Curve
  KI_tolerances_too_tight   tolerance too tight
  KI_bad_precision          tol less than modelling resolution

Description:
  CRSPTC approximates 't_cu' which lies approximately on 'surf' by an
  SP_Curve or series of SP_Curves, lying on 'surf'.

  The arguments are

  Basis surface 'surf'.

  . Surface upon which to create SP_Curve(s), 'surf' forms the basis surface
    of the new SP_curve(s).

  . If 'surf' is construction geometry or is attached to a face, within a
    body, the SP-curve will be created as construction geometry
    in that body, and may only be attached to topology within that body.

  Trimmed Curve 't_cu'.

  . Trimmed curve to be approximated by SP_curve(s)

  . Lies approximately on 'surf'. Note that if the trimmed curve is
    sufficiently long to overhang the ENSUPA range of a limited surface,
    then the surface may be extended in order to accommodate the SP-curve(s).

  Required tolerance 'tol'

  . The SP_Curve will be created to the distance tolerance 'tol', i.e. it
    lies within 'tol' of the image of 't_cu' in the surface. The image of
    't_cu' in this context means the curve formed by the locus of points
    on 'surf' closest to corresponding points on 't_cu'.

  . If the required tolerance cannot be met then the function will fail with
    error KI_tolerances_too_tight indicating that a larger tolerance may allow a
    successful approximation.

  Production of zero length sp_curves 'degen'.

  . Sp_curves may start or end on surface degeneracies, may lie entirely
    within them, but may not pass through them. A trimmed curve which passes
    through a surface degeneracy will be approximated by at least two
    SP_Curves. If 'degens' is true a zero length SP_Curve will be returned
    which joins the otherwise disjoint SP_Curves in parameter space. Zero
    length SP_Curves may not be attached to a model.

  SP_curve sense 'sense'

  . If 'sense' is true the created SP_Curve will have the same sense as the
    trimmed curve in that it starts at the trimmed curve start. If 'sense'
    is false the SP_Curve will start at the trimmed curve end and end at the
    trimmed curve start.


  The returns are

  List of SP_Curves 'spc' of length 'nspc'.

  Ownership:

  The ownership of the newly created SP_Curve(s) is determined by the ownership
  of 'surf' as follows

      |____________________|___________________|
      | 'surf' owner       | SP_Curve owner    |
      |____________________|___________________|
      | World              | World             |
      | Assembly           | Assembly          |
      | Body               | Body              |
      | Face               | Body owning face  |
      _____________________|___________________|