PK_BCURVE_splinewise_sf_t

struct PK_BCURVE_splinewise_sf_s
    {
    int                   degree;           --- The degree = order-1.
    int                   n_positions;      --- The number of positions
    PK_VECTOR_t          *positions;        --- The positions
    PK_PARAM_end_t        t_end;            --- End condition at lower t
    PK_PARAM_end_t        T_end;            --- End condition at upper T
    PK_VECTOR_t           t_deriv;          --- Derivative at lower t
    PK_VECTOR_t           T_deriv;          --- Derivative at upper T
    PK_PARAM_knot_t       how_knot;         --- How knot vector defined
    double               *knot;             --- Knot vector
    };
typedef struct PK_BCURVE_splinewise_sf_s PK_BCURVE_splinewise_sf_t;


This data structure is the splinewise standard form of a 3D b-curve.


Specific Errors:
    PK_ERROR_incompatible_props     only one end is periodic or a periodic
                                    curve has coincident end points (MILD)
    PK_ERROR_bad_derivative         't_deriv' or 'T_deriv' too large (MILD)
    PK_ERROR_insufficient_points    not enough spline points (MILD)
    PK_ERROR_coincident_points      repeated spline points (MILD)
    PK_ERROR_bad_position           a spline point is outside size box (MILD)
    PK_ERROR_bad_knots              bad parameterisation (MILD)
    PK_ERROR_repeated_knots         repeated knots (MILD)
    PK_ERROR_wrong_number_knots     wrong number of knots (MILD)
    PK_ERROR_bad_order              degree < 0 or degree > 3 or
                                    degree < 2 and supplied clamping vectors
                                    are incorrect (MILD)

Used in:

PK_BCURVE_ask_splinewise
PK_BCURVE_create_splinewise

'degree'         Curve degree.
                 When the standard form is input to Parasolid
                 (PK_BCURVE_create_splinewise), 'degree' may only be set to 3
                 to produce cubic curves or 0 in which case Parasolid will
                 select an appropriate degree.

'n_positions'    Number of positions.
                 If 't_end' is PK_PARAM_end_periodic_c then 'n_positions'
                 must be at least 3, otherwise 'n_positions' must be at
                 least 2.

'positions'      Array of positions.
                 Consecutive positions must not coincide.
                 For a closed, non-periodic curve the start and end
                 positions must coincide.
                 For a periodic curve the start and end positions must not
                 coincide.

't_end'          End condition at lower t (i.e. start of curve).
                 If this is PK_PARAM_end_periodic_c then 'T_end' must also be
                 PK_PARAM_end_periodic_c.
                 If this is PK_PARAM_end_clamped_vector_c then 't_deriv' must
                 be set to the start derivative.

'T_end'          End condition at upper T (i.e. end of curve).
                 If this is PK_PARAM_end_periodic_c then 't_end' must also be
                 PK_PARAM_end_periodic_c.
                 If this is PK_PARAM_end_clamped_vector_c then 'T_deriv'
                 must be set to the end derivative.

't_deriv'        Derivative at start of curve if 't_end' is
                 PK_PARAM_end_clamped_vector_c.

'T_deriv'        Derivative at end of curve if 'T_end' is
                 PK_PARAM_end_clamped_vector_c.

                 The derivatives in 't_deriv' and 'T_deriv' should be supplied
                 with respect to a parameter which varies from 0 to 1 between
                 the first or last two 'positions' (as appropriate). In other
                 words, the derivatives should have dimensions of length. The
                 magnitude is significant, and supplying vectors which are too
                 large may cause the curve to loop or have tight curvature.

'how_knot'       How the knot vector is defined.

'knot'           If 'how_knot' is PK_PARAM_knot_defined_c then 'knot' is the
                 knot vector of length 'n_positions' if the curve is not
                 periodic or 'n_positions' + 1 if the curve is periodic.
                 If 'how_knot' is PK_PARAM_knot_auto_c then 'knot' is ignored.