GIS-判断点是否落在指点的多边形区域内

/// <summary>
        /// 判断坐标点是否落在指定的多边形区域内
        /// </summary>
        /// <param name="point">指定的坐标点</param>
        /// <param name="list">多变形区域的节点集合</param>
        /// <returns>True 落在范围内 False 不在范围内</returns>
        public bool IsWithIn(ESRI.ArcGIS.Client.Geometry.MapPoint point, List<ESRI.ArcGIS.Client.Geometry.MapPoint> list)
        {
            double x = point.X;
            double y = point.Y;

            int isum, icount, index;
            double dLon1 = 0, dLon2 = 0, dLat1 = 0, dLat2 = 0, dLon;

            if (list.Count < 3)
            {
                return false;
            }

            isum = 0;
            icount = list.Count;

            try
            {
                for (index = 0; index < icount - 1; index++)
                {
                    if (index == icount - 1)
                    {
                        dLon1 = list[index].X;
                        dLat1 = list[index].Y;
                        dLon2 = list[0].X;
                        dLat2 = list[0].Y;
                    }
                    else
                    {
                        dLon1 = list[index].X;
                        dLat1 = list[index].Y;
                        dLon2 = list[index + 1].X;
                        dLat2 = list[index + 1].Y;
                    }

                    if (((y >= dLat1) && (y < dLat2)) || ((y >= dLat2) && (y < dLat1)))
                    {
                        if (Math.Abs(dLat1 - dLat2) > 0)
                        {
                            dLon = dLon1 - ((dLon1 - dLon2) * (dLat1 - y)) / (dLat1 - dLat2);
                            if (dLon < x)
                                isum++;
                        }
                    }
                }
            }
            catch { }

            if ((isum % 2) != 0)
            {
                return true;
            }
            else
            {
                return false;
            }
        }