给定n个点:
p0, p1, p2, ..., pn;
如何获得点c1、c2,以使由
p0、c1、c2、pn
定义的三次贝塞尔曲线最接近给定的点?
我试过最小二乘法。在阅读http://www.mathworks.com/matlabcentral/fileexchange/15542-cubic-bezier-least-square-fitting的pdf文档之后,我写出了这个方法。但是我找不到一个好的t(i)函数。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows;
namespace BezierFitting
{
class CubicBezierFittingCalculator
{
private List<Point> data;
public CubicBezierFittingCalculator(List<Point> data)
{
this.data = data;
}
private double t(int i)
{
return (double)(i - 1) / (data.Count - 1);
// double s = 0.0, d = 0.0;
//
// for (int j = 1; j < data.Count; j++)
// {
// if (j < i)
// {
// s += (data[j] - data[j - 1]).Length;
// }
// d += (data[j] - data[j - 1]).Length;
// }
// return s / d;
}
public void Calc(ref Point p1, ref Point p2)
{
double n = data.Count;
Vector p0 = (Vector)data.First();
Vector p3 = (Vector)data.Last();
double a1 = 0.0, a2 = 0.0, a12 = 0.0;
Vector c1 = new Vector(0.0, 0.0), c2 = new Vector(0.0, 0.0);
for (int i = 1; i <= n; i++)
{
double ti = t(i), qi = 1 - ti;
double ti2 = ti * ti, qi2 = qi * qi;
double ti3 = ti * ti2, qi3 = qi * qi2;
double ti4 = ti * ti3, qi4 = qi * qi3;
a1 += ti2 * qi4;
a2 += ti4 * qi2;
a12 += ti3 * qi3;
Vector pi = (Vector)data[i - 1];
Vector m = pi - qi3 * p0 - ti3 * p3;
c1 += ti * qi2 * m;
c2 += ti2 * qi * m;
}
a1 *= 9.0;
a2 *= 9.0;
a12 *= 9.0;
c1 *= 3.0;
c2 *= 3.0;
double d = a1 * a2 - a12 * a12;
p1 = (Point)((a2 * c1 - a12 * c2) / d);
p2 = (Point)((a1 * c2 - a12 * c1) / d);
}
}
}
如何得到与给定点最接近的立方贝塞尔曲线?
例如,这里有30个点:
22, 245
26, 240
39, 242
51, 231
127, 189
136, 185
140, 174
147, 171
163, 162
169, 155
179, 107
181, 147
189, 168
193, 187
196, 75
199, 76
200, 185
201, 68
204, 73
205, 68
208, 123
213, 118
216, 210
216, 211
218, 68
226, 65
227, 110
228, 102
229, 87
252, 247
这些点分布在由四个点控制的立方贝塞尔曲线周围:
P0 (0, 256), P1 (512, 0), P2 (0, 0), P3 (256, 256)。
假设曲线从(0,256)到(256,256),如何获得靠近原始点的另外两个控制点?