CRSPCU ( surf, dim, order, nctrl, ctrl, knots, period, split, nspc, spc, 
=========================================================================
         ifail )
         =======

  Create SP-curve(s) from B-spline data defined in surface parameter space.

Receives:
  KI_tag_surface           *surf           --- basis surface for SP-curve
  int                      *dim            --- dimension of control points
  KI_int_order             *order          --- order of curve
  KI_int_nitems            *nctrl          --- number of control points
  KI_dbl_coefficients       ctrl[dim*nctrl] --- control points
  KI_dbl_knots              knots[]        --- knot vector
  KI_cod_logical           *period         --- periodic flag
  KI_cod_logical           *split          --- split flag

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_invalid_geometry       invalid spcurves
  KI_bad_knots              invalid knot vector
  KI_weight_le_0            weights are non positive
                            weights are non-positive
  KI_insufficient_points    insufficient control points
  KI_bad_dimension          dimension must be 2 or 3
  KI_linear_multi_seg       multi-segment linear curves not allowed
  KI_order_lt_2             order must be at least 2

Description:
  Creates an SP-curve on a surface from B-spline data defined in the surface
  parameter space.

  An SP-curve must be G1 continuous, and if periodic must meet itself with
  G1 continuity, an SP_curve may start or end on a surface degeneracy or
  singularity, surface degeneracies may only appear elsewhere on the curve
  if the entire curve lies within the degeneracy.

  The arguments are:

  Basis surface 'surf' of SP-curve.

  . This is the surface in whose parameter space the curve
    is defined. The surface parameters are u and v in what follows.

  . 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.


  Dimension of control points 'dim':

  . For rational curves 'dim' = 3.

  . For non-rational curves 'dim' = 2.

  Order of the curve 'order':

  . The order of the curve = degree + 1.

  . The minimum order is 2.

  . An order 2 B-Spline may consist of one segment only.

  Number of control points 'nctrl':

  . 'nctrl' >= 'order'.

  Control points 'ctrl':

  . For non-rational curves, the control points are points in the
    parameter space of 'surf'. They must be supplied as [u0,v0,u1,v1...].

  . For rational curves each vector contains a point in parameter space
    followed by a weight for the point. The points are supplied
    [u0,v0,w0,u1,v1,w1...]. The weights must be positive.

  . The (u,v) values defining control points do not have to lie within the
    parameter range defined by ENSUPA on limited surfaces, though ideally the
    B-spline curve so defined will be. If this is not the case, then an
    attempt will be made to extend the surface so that the curve lies wholly
    within it.

  . The curve must be G1 continuous in parameter space, so that linear
    curves of >1 segment are not allowed.

  . The curve will NOT be checked for self-intersection.

  Knot vector 'knots':

  . The knot values must form a non-decreasing sequence.

  . The B-Spline may be closed, and may be periodic.

  . For non-periodic B-Splines there must be ('nctrl' + 'order') knot values,
    the maximum multiplicity of an internal knot value is ('order' - 1), and
    the maximum multiplicity of an end knot value is 'order'.

  . For periodic B-Splines there must be ('nctrl' + 1 ) knot values, the
    maximum multiplicity of any knot value is ('order' - 1). If the periodic
    knot has multiplicity greater than 1, repetitions must be given at the
    end of the knot vector.

  Periodic flag 'period':

  . The B-Spline may be periodic if it is closed and meets itself with G1
    continuity, and the resulting three space SP-Curve is also closed and
    and meets itself with G1 continuity.

  Split flag 'split':

  . If 'split' is set true an ordered list of SP-Curves will be returned
    which satisfy continuity requirements. Care should still be taken that
    the degeneracy conditions are met. The flag may be turned off when it
    is known that the resulting single SP-Curve is valid.


  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  |
      _____________________|___________________|

  Periodics:

  If a single SP_Curve is returned, it will be periodic if the periodic flag
  'period' was set KI_true. If 'period' was set KI_false but the SP_Curve is
  closed and G1 continuous, Parasolid may choose to treat the curve as
  periodic. OUSPCU is not affected and returns bspline data as received by
  CRSPCU, ENCUPA will however reflect this internal periodicity.