/// <summary>
        /// 多边形面积计算(不论凸凹)
        /// </summary>
        /// <param name="N">坐标点数即多边形的边数</param>
        /// <param name="X">坐标的横坐标集合</param>
        /// <param name="Y">坐标的纵坐标集合</param>
        /// <returns>多边形的面积</returns>
        public static double Area(int N, double[] X, double[] Y)
        {
            double area;
            if (N < 3)
            {
                return 0;
            }
            area = Y[0] * (X[N - 1] - X[1]);
            for (int i = 1; i < N; i++)
            {
                area += Y * (X[(i - 1)] - X[(i + 1) % N]);
            }
            return area / 2;
        }