点到线段的最短距离

private double pointToLine(int x1, int y1, int x2, int y2, int x0,
int y0) {
double space = 0;
double a, b, c;
a = lineSpace(x1, y1, x2, y2);// 线段的长度
b = lineSpace(x1, y1, x0, y0);// (x1,y1)到点的距离
c = lineSpace(x2, y2, x0, y0);// (x2,y2)到点的距离
if (c <= 0.000001 || b <= 0.000001) {
space = 0;
return space;
}
if (a <= 0.000001) {
space = b;
return space;
}
if (c * c >= a * a + b * b) {
space = b;
return space;
}
if (b * b >= a * a + c * c) {
space = c;
return space;
}
double p = (a + b + c) / 2;// 半周长
double s = Math.sqrt(p * (p - a) * (p - b) * (p - c));// 海伦公式求面积
space = 2 * s / a;// 返回点到线的距离（利用三角形面积公式求高）
return space;
}

// 计算两点之间的距离
private double lineSpace(int x1, int y1, int x2, int y2) {
double lineLength = 0;
lineLength = Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2)
* (y1 - y2));
return lineLength;

}