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Next: Distance Tolerance Up: Fairing of B-Spline Curves Previous: The New Control Point

The Ranking-List

The best location has now be found by changing a control point. Solving the next problem is to determine the faired control point. That means we have to find the index $r$ of the control point.

We want to change the control point where the largest improvement of the fairness functional is given. We call this improvement

\begin{displaymath}
z_r = E_l(\bar{\bf d}_r) - E_l(\widetilde{\bf d}_r) \ge 0
\end{displaymath}
(17)

ranking-number. Following up some calculations we obtain by inserting the control point $\widetilde{\bf d}_r$ (14)
\begin{displaymath}
z_r =
\left(\bar{\bf d}_r - \widetilde{\bf d}_r \right)^2 \cdot
\int_a^b \left( N_{r,k}^{(l)}(t) \right)^2 \; dt\;\;\;.
\end{displaymath}
(18)

This ranking-number is a weighted function of the squared change of control point $\bar{\bf d}_r$.

The ranking-numbers have to be calculated for all involved control in order to find the largest improvement. This ranking-list then has to be sorted.

The whole ranking-list has to be calculated only in the first step for all control points because the control point $\widetilde{\bf d}_r$ influences only the ranking-numbers $z_i$ with the index $r - k + 1\le i \le r + k - 1$ and these ranking-numbers only have to be recalculated in the following step.