NURB Curves

A nonuniform rational B-spline (NURB) curve is a three-dimensional projection of a four-dimensional curve, with an optional set of attributes. A NURB curve is defined by the TQ3NURBCurveData data type. See "Creating and Editing NURB Curves" for a description of the routines you can use to create and edit NURB curves. Figure 29 shows a NURB curve.



 
typedef struct TQ3NURBCurveData {

    unsigned long                       order;

    unsigned long                       numPoints;

    TQ3RationalPoint4D                  *controlPoints;

    float                               *knots;

    TQ3AttributeSet                     curveAttributeSet;

} TQ3NURBCurveData;

Figure 29 A NURB curve

order: The order of the NURB curve. For NURB curves defined by ratios of cubic B-spline polynomials, the order is 4. In general, the order of a NURB curve defined by polynomial equations of degree n is n +1. The value in this field must be greater than 1.
numPoints: The number of control points that define the NURB curve. The value in this field must be greater than or equal to the order of the NURB curve.
controlPoints: A pointer to an array of rational four-dimensional control points that define the NURB curve.
knots: A pointer to an array of knots that define the NURB curve. The number of knots in a NURB curve is the sum of the values in the order and numPoints fields. The values in this array must be nondecreasing (but successive values may be equal, up to a multiplicity equivalent to the order of the curve).
curveAttributeSet: A set of attributes for the NURB curve. The value in this field is NULL if no NURB curve attributes are defined.