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;

}