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# Global B-Spline Curve Interpolation

This Demonstration shows the method of global B-spline curve interpolation. The implementation is fully described in the Details.

### DETAILS

Given a set of points , , this Demonstration interpolates between these points using a degree nonrational B-spline curve. Assigning a parameter value to each and selecting an appropriate knot vector leads to the system of linear equations
. (1)
The control points are the unknowns. Let be the number of coordinates in the (typically 2, 3, or 4). Equation (1) has one coefficient matrix with elements in the right-hand column and, correspondingly, solution sets for the coordinates of the .
The problem of choosing the and remains; their choice affects the shape and parametrization of the curve. Assume that the parameter lies in the range . Three common methods of choosing the are, with ():
Equal spacing:
, , , (2)
Chord length:
let , then
, , (3)
Centripetal:
let , then
, , (4)
Lastly, the following method was used to generate the knots ():
, , . (5)
Here is an example of an application of this algorithm:
Let , and assume the interpolation is a cubic curve. Use equations (3) and (5) to compute the and , and then set up the system of linear equations, equation (1). The separate chord lengths are given by
, , , and the total chord length is . Thus
, , , , .
So .
Thus
The system of linear equations is then represented by
Reference
[1] L. Piegl and W. Tiller, The NURBS Book, 2nd ed., Berlin: Springer–Verlag, 1997.

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