geohash算法原理及实现方式

1 using System;
  2 
  3 namespace sharonjl.utils
  4 {
  5     public static class Geohash
  6     {
  7         #region Direction enum
  8 
  9         public enum Direction
 10         {
 11             Top = 0,
 12             Right = 1,
 13             Bottom = 2,
 14             Left = 3 
 15         }
 16 
 17         #endregion
 18 
 19         private const string Base32 = "0123456789bcdefghjkmnpqrstuvwxyz";
 20         private static readonly int[] Bits = new[] {16, 8, 4, 2, 1};
 21 
 22         private static readonly string[][] Neighbors = {
 23                                                            new[]
 24                                                                {
 25                                                                    "p0r21436x8zb9dcf5h7kjnmqesgutwvy", // Top
 26                                                                    "bc01fg45238967deuvhjyznpkmstqrwx", // Right
 27                                                                    "14365h7k9dcfesgujnmqp0r2twvyx8zb", // Bottom
 28                                                                    "238967debc01fg45kmstqrwxuvhjyznp", // Left
 29                                                                }, new[]
 30                                                                       {
 31                                                                           "bc01fg45238967deuvhjyznpkmstqrwx", // Top
 32                                                                           "p0r21436x8zb9dcf5h7kjnmqesgutwvy", // Right
 33                                                                           "238967debc01fg45kmstqrwxuvhjyznp", // Bottom
 34                                                                           "14365h7k9dcfesgujnmqp0r2twvyx8zb", // Left
 35                                                                       }
 36                                                        };
 37 
 38         private static readonly string[][] Borders = {
 39                                                          new[] {"prxz", "bcfguvyz", "028b", "0145hjnp"},
 40                                                          new[] {"bcfguvyz", "prxz", "0145hjnp", "028b"}
 41                                                      };
 42 
 43         public static String CalculateAdjacent(String hash, Direction direction)
 44         {
 45             hash = hash.ToLower();
 46 
 47             char lastChr = hash[hash.Length - 1];
 48             int type = hash.Length%2;
 49             var dir = (int) direction;
 50             string nHash = hash.Substring(0, hash.Length - 1);
 51 
 52             if (Borders[type][dir].IndexOf(lastChr) != -1)
 53             {
 54                 nHash = CalculateAdjacent(nHash, (Direction) dir);
 55             }
 56             return nHash + Base32[Neighbors[type][dir].IndexOf(lastChr)];
 57         }
 58 
 59         public static void RefineInterval(ref double[] interval, int cd, int mask)
 60         {
 61             if ((cd & mask) != 0)
 62             {
 63                 interval[0] = (interval[0] + interval[1])/2;
 64             }
 65             else
 66             {
 67                 interval[1] = (interval[0] + interval[1])/2;
 68             }
 69         }
 70 
 71         public static double[] Decode(String geohash)
 72         {
 73             bool even = true;
 74             double[] lat = {-90.0, 90.0};
 75             double[] lon = {-180.0, 180.0};
 76 
 77             foreach (char c in geohash)
 78             {
 79                 int cd = Base32.IndexOf(c);
 80                 for (int j = 0; j < 5; j++)
 81                 {
 82                     int mask = Bits[j];
 83                     if (even)
 84                     {
 85                         RefineInterval(ref lon, cd, mask);
 86                     }
 87                     else
 88                     {
 89                         RefineInterval(ref lat, cd, mask);
 90                     }
 91                     even = !even;
 92                 }
 93             }
 94 
 95             return new[] {(lat[0] + lat[1])/2, (lon[0] + lon[1])/2};
 96         }
 97 
 98         public static String Encode(double latitude, double longitude, int precision = 12)
 99         {
100             bool even = true;
101             int bit = 0;
102             int ch = 0;
103             string geohash = "";
104 
105             double[] lat = {-90.0, 90.0};
106             double[] lon = {-180.0, 180.0};
107 
108             if (precision < 1 || precision > 20) precision = 12;
109 
110             while (geohash.Length < precision)
111             {
112                 double mid;
113 
114                 if (even)
115                 {
116                     mid = (lon[0] + lon[1])/2;
117                     if (longitude > mid)
118                     {
119                         ch |= Bits[bit];
120                         lon[0] = mid;
121                     }
122                     else
123                         lon[1] = mid;
124                 }
125                 else
126                 {
127                     mid = (lat[0] + lat[1])/2;
128                     if (latitude > mid)
129                     {
130                         ch |= Bits[bit];
131                         lat[0] = mid;
132                     }
133                     else
134                         lat[1] = mid;
135                 }
136 
137                 even = !even;
138                 if (bit < 4)
139                     bit++;
140                 else
141                 {
142                     geohash += Base32[ch];
143                     bit = 0;
144                     ch = 0;
145                 }
146             }
147             return geohash;
148         }
149     }
150 }