海伦公式计算面积

        /// <summary>
        /// 已知三角形三个边用海伦公式计算面积
        /// </summary>
        /// <param name="alength">a边长</param>
        /// <param name="blength">b边长</param>
        /// <param name="clength">c边长</param>
        /// <returns>面积</returns>
        private double GetHeight(double alength, double blength, double clength)
        {
            double S, p;
            if ((alength + blength > clength) && (alength + clength > blength) && (blength + clength > alength))
            {
                p = (alength + blength + clength) / 2;
                S = Math.Sqrt(p * (p - alength) * (p - blength) * (p - clength));
            }
            else
            {
                S = 0;
            }

            return S;
        }