GeoHash C#版 找到周围8个区域的GeoHash编码

相信找到这里的 ，geohash算法原理及实现方式应该也有所了解了。原代码了出自
邓星林博客
http://www.cnblogs.com/dengxinglin/archive/2012/12/14/2817761.html
自已找来，加上8个区的实现，加些注释和例子，测试已经ok。网上只有java版，这里让大家少起弯路

using System;

namespace sharonjl.utils
{
    public static class Geohash
    {
        #region Direction enum

        public enum Direction
        {
            Top = 0,
            Right = 1,
            Bottom = 2,
            Left = 3 
        }

        #endregion

        private const string Base32 = "0123456789bcdefghjkmnpqrstuvwxyz";
        private static readonly int[] Bits = new[] {16, 8, 4, 2, 1};

        private static readonly string[][] Neighbors = {
                                                           new[]
                                                               {
                                                                   "p0r21436x8zb9dcf5h7kjnmqesgutwvy", // Top
                                                                   "bc01fg45238967deuvhjyznpkmstqrwx", // Right
                                                                   "14365h7k9dcfesgujnmqp0r2twvyx8zb", // Bottom
                                                                   "238967debc01fg45kmstqrwxuvhjyznp", // Left
                                                               }, new[]
                                                                      {
                                                                          "bc01fg45238967deuvhjyznpkmstqrwx", // Top
                                                                          "p0r21436x8zb9dcf5h7kjnmqesgutwvy", // Right
                                                                          "238967debc01fg45kmstqrwxuvhjyznp", // Bottom
                                                                          "14365h7k9dcfesgujnmqp0r2twvyx8zb", // Left
                                                                      }
                                                       };

        private static readonly string[][] Borders = {
                                                         new[] {"prxz", "bcfguvyz", "028b", "0145hjnp"},
                                                         new[] {"bcfguvyz", "prxz", "0145hjnp", "028b"}
                                                     };
        /// <summary>
        /// 计算相邻
        /// </summary>
        /// <param name="hash"></param>
        /// <param name="direction"></param>
        /// <returns></returns>
        public static String CalculateAdjacent(String hash, Direction direction)
        {
            hash = hash.ToLower();

            char lastChr = hash[hash.Length - 1];
            int type = hash.Length%2;
            var dir = (int) direction;
            string nHash = hash.Substring(0, hash.Length - 1);

            if (Borders[type][dir].IndexOf(lastChr) != -1)
            {
                nHash = CalculateAdjacent(nHash, (Direction) dir);
            }
            return nHash + Base32[Neighbors[type][dir].IndexOf(lastChr)];
        }
        /// <summary>
        /// 细化间隔
        /// </summary>
        /// <param name="interval"></param>
        /// <param name="cd"></param>
        /// <param name="mask"></param>
        public static void RefineInterval(ref double[] interval, int cd, int mask)
        {
            if ((cd & mask) != 0)
            {
                interval[0] = (interval[0] + interval[1])/2;
            }
            else
            {
                interval[1] = (interval[0] + interval[1])/2;
            }
        }

        /// <summary>
        /// 解码
        /// </summary>
        /// <param name="geohash"></param>
        /// <returns></returns>
        public static double[] Decode(String geohash)
        {
            bool even = true;
            double[] lat = {-90.0, 90.0};
            double[] lon = {-180.0, 180.0};

            foreach (char c in geohash)
            {
                int cd = Base32.IndexOf(c);
                for (int j = 0; j < 5; j++)
                {
                    int mask = Bits[j];
                    if (even)
                    {
                        RefineInterval(ref lon, cd, mask);
                    }
                    else
                    {
                        RefineInterval(ref lat, cd, mask);
                    }
                    even = !even;
                }
            }

            return new[] {(lat[0] + lat[1])/2, (lon[0] + lon[1])/2};
        }
        /// <summary>
        /// 编码
        /// </summary>
        /// <param name="latitude">纬度</param>
        /// <param name="longitude">经度</param>
        /// <param name="precision">精度</param>
        /// <returns></returns>
        public static String Encode(double latitude, double longitude, int precision = 12)
        {
            bool even = true;
            int bit = 0;
            int ch = 0;
            string geohash = "";

            double[] lat = {-90.0, 90.0};
            double[] lon = {-180.0, 180.0};

            if (precision < 1 || precision > 20) precision = 12;

            while (geohash.Length < precision)
            {
                double mid;

                if (even)
                {
                    mid = (lon[0] + lon[1])/2;
                    if (longitude > mid)
                    {
                        ch |= Bits[bit];
                        lon[0] = mid;
                    }
                    else
                        lon[1] = mid;
                }
                else
                {
                    mid = (lat[0] + lat[1])/2;
                    if (latitude > mid)
                    {
                        ch |= Bits[bit];
                        lat[0] = mid;
                    }
                    else
                        lat[1] = mid;
                }

                even = !even;
                if (bit < 4)
                    bit++;
                else
                {
                    geohash += Base32[ch];
                    bit = 0;
                    ch = 0;
                }
            }
            return geohash;
        }

        /// <summary>
        /// 获取九个格子 顺序 本身 上、下、左、右、 左上、 右上、 左下、右下
        /// </summary>
        /// <param name="geohash"></param>
        /// <returns></returns>
        public static String[] getGeoHashExpand(String geohash)
        { 
        
        try {
            String geohashTop = CalculateAdjacent(geohash, Direction.Top);//上

            String geohashBottom = CalculateAdjacent(geohash, Direction.Bottom);//下

            String geohashLeft = CalculateAdjacent(geohash, Direction.Left);//左

            String geohashRight = CalculateAdjacent(geohash, Direction.Right);//右


            String geohashTopLeft = CalculateAdjacent(geohashLeft, Direction.Top);//左上

            String geohashTopRight = CalculateAdjacent(geohashRight, Direction.Top);//右上

            String geohashBottomLeft = CalculateAdjacent(geohashLeft, Direction.Bottom);//左下

            String geohashBottomRight = CalculateAdjacent(geohashRight, Direction.Bottom);//右下

            String[] expand = { geohash, geohashTop, geohashBottom, geohashLeft, geohashRight, geohashTopLeft, geohashTopRight,  geohashBottomLeft, geohashBottomRight};
            return expand;
        } catch (Exception e) {
            return null;
        }
        }


        ///// <summary>
        ///// test 
        ///// </summary>
        ///// <param name="args"></param>
        //public  void main()
        //{
        //    double lat = 39.90403;
        //    double lon = 116.407526; //需要查询经纬度，目前指向的是BeiJing
        //    string hash = Geohash.Encode(lat, lon);
        //    int geohashLen = 6;
        //    /*获取中心点的geohash*/
        //    String geohash = hash.Substring(0, geohashLen);
        //    /*获取所有的矩形geohash， 一共是九个 ，包含中心点,打印顺序请参考参数*/
        //    String[] result = Geohash.getGeoHashExpand(geohash);
        //}
    }
}