private double pointToLine(Vector2 point1, Vector2 point2, Vector2 position)//point1和point2為線的兩個端點
    {
        double space = 0;
        double a, b, c;
        a = Vector2.Distance(point1,point2);// 線段的長度      
        b = Vector2.Distance(point1, position);// position到點point1的距離      
        c = Vector2.Distance(point2, position);// position到point2點的距離 
        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;// 半周長      
        double s = Math.Sqrt(p * (p - a) * (p - b) * (p - c));// 海倫公式求面積      
        space = 2 * s / a;// 返回點到線的距離（利用三角形面積公式求高）      
        return space;
    }