1 <?php

  2 /**

  3  * Geohash generation class

  4  * http://blog.dixo.net/downloads/

  5  *

  6  * This file copyright (C) 2008 Paul Dixon (paul@elphin.com)

  7  *

  8  * This program is free software; you can redistribute it and/or

  9  * modify it under the terms of the GNU General Public License

 10  * as published by the Free Software Foundation; either version 3

 11  * of the License, or (at your option) any later version.

 12  *

 13  * This program is distributed in the hope that it will be useful,

 14  * but WITHOUT ANY WARRANTY; without even the implied warranty of

 15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 16  * GNU General Public License for more details.

 17  *

 18  * You should have received a copy of the GNU General Public License

 19  * along with this program; if not, write to the Free Software

 20  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

 21  */

 22

 23

 24

 25 /**

 26 * Encode and decode geohashes

 27 *

 28 */

 29 class Geohash

 30 {

 31     private $coding="0123456789bcdefghjkmnpqrstuvwxyz";

 32     private $codingMap=array();

 33

 34     public function Geohash()

 35     {

 36         //build map from encoding char to 0 padded bitfield

 37         for($i=0; $i<32; $i++)

 38         {

 39             $this->codingMap[substr($this->coding,$i,1)]=str_pad(decbin($i), 5, "0", STR_PAD_LEFT);

 40         }

 41

 42     }

 43

 44     /**

 45     * Decode a geohash and return an array with decimal lat,long in it

 46     */

 47     public function decode($hash)

 48     {

 49         //decode hash into binary string

 50         $binary="";

 51         $hl=strlen($hash);

 52         for($i=0; $i<$hl; $i++)

 53         {

 54             $binary.=$this->codingMap[substr($hash,$i,1)];

 55         }

 56

 57         //split the binary into lat and log binary strings

 58         $bl=strlen($binary);

 59         $blat="";

 60         $blong="";

 61         for ($i=0; $i<$bl; $i++)

 62         {

 63             if ($i%2)

 64                 $blat=$blat.substr($binary,$i,1);

 65             else

 66                 $blong=$blong.substr($binary,$i,1);

 67

 68         }

 69

 70         //now concert to decimal

 71         $lat=$this->binDecode($blat,-90,90);

 72         $long=$this->binDecode($blong,-180,180);

 73

 74         //figure out how precise the bit count makes this calculation

 75         $latErr=$this->calcError(strlen($blat),-90,90);

 76         $longErr=$this->calcError(strlen($blong),-180,180);

 77

 78         //how many decimal places should we use? There's a little art to

 79         //this to ensure I get the same roundings as geohash.org

 80         $latPlaces=max(1, -round(log10($latErr))) - 1;

 81         $longPlaces=max(1, -round(log10($longErr))) - 1;

 82

 83         //round it

 84         $lat=round($lat, $latPlaces);

 85         $long=round($long, $longPlaces);

 86

 87         return array($lat,$long);

 88     }

 89

 90

 91     /**

 92     * Encode a hash from given lat and long

 93     */

 94     public function encode($lat,$long)

 95     {

 96         //how many bits does latitude need?

 97         $plat=$this->precision($lat);

 98         $latbits=1;

 99         $err=45;

100         while($err>$plat)

101         {

102             $latbits++;

103             $err/=2;

104         }

105

106         //how many bits does longitude need?

107         $plong=$this->precision($long);

108         $longbits=1;

109         $err=90;

110         while($err>$plong)

111         {

112             $longbits++;

113             $err/=2;

114         }

115

116         //bit counts need to be equal

117         $bits=max($latbits,$longbits);

118

119         //as the hash create bits in groups of 5, lets not

120         //waste any bits - lets bulk it up to a multiple of 5

121         //and favour the longitude for any odd bits

122         $longbits=$bits;

123         $latbits=$bits;

124         $addlong=1;

125         while (($longbits+$latbits)%5 != 0)

126         {

127             $longbits+=$addlong;

128             $latbits+=!$addlong;

129             $addlong=!$addlong;

130         }

131

132

133         //encode each as binary string

134         $blat=$this->binEncode($lat,-90,90, $latbits);

135         $blong=$this->binEncode($long,-180,180,$longbits);

136

137         //merge lat and long together

138         $binary="";

139         $uselong=1;

140         while (strlen($blat)+strlen($blong))

141         {

142             if ($uselong)

143             {

144                 $binary=$binary.substr($blong,0,1);

145                 $blong=substr($blong,1);

146             }

147             else

148             {

149                 $binary=$binary.substr($blat,0,1);

150                 $blat=substr($blat,1);

151             }

152             $uselong=!$uselong;

153         }

154

155         //convert binary string to hash

156         $hash="";

157         for ($i=0; $i<strlen($binary); $i+=5)

158         {

159             $n=bindec(substr($binary,$i,5));

160             $hash=$hash.$this->coding[$n];

161         }

162

163

164         return $hash;

165     }

166

167     /**

168     * What's the maximum error for $bits bits covering a range $min to $max

169     */

170     private function calcError($bits,$min,$max)

171     {

172         $err=($max-$min)/2;

173         while ($bits--)

174             $err/=2;

175         return $err;

176     }

177

178     /*

179     * returns precision of number

180     * precision of 42 is 0.5

181     * precision of 42.4 is 0.05

182     * precision of 42.41 is 0.005 etc

183     */

184     private function precision($number)

185     {

186         $precision=0;

187         $pt=strpos($number,'.');

188         if ($pt!==false)

189         {

190             $precision=-(strlen($number)-$pt-1);

191         }

192

193         return pow(10,$precision)/2;

194     }

195

196

197     /**

198     * create binary encoding of number as detailed in http://en.wikipedia.org/wiki/Geohash#Example

199     * removing the tail recursion is left an exercise for the reader

200     */

201     private function binEncode($number, $min, $max, $bitcount)

202     {

203         if ($bitcount==0)

204             return "";

205

206         #echo "$bitcount: $min $max<br>";

207

208         //this is our mid point - we will produce a bit to say

209         //whether $number is above or below this mid point

210         $mid=($min+$max)/2;

211         if ($number>$mid)

212             return "1".$this->binEncode($number, $mid, $max,$bitcount-1);

213         else

214             return "0".$this->binEncode($number, $min, $mid,$bitcount-1);

215     }

216

217

218     /**

219     * decodes binary encoding of number as detailed in http://en.wikipedia.org/wiki/Geohash#Example

220     * removing the tail recursion is left an exercise for the reader

221     */

222     private function binDecode($binary, $min, $max)

223     {

224         $mid=($min+$max)/2;

225

226         if (strlen($binary)==0)

227             return $mid;

228

229         $bit=substr($binary,0,1);

230         $binary=substr($binary,1);

231

232         if ($bit==1)

233             return $this->binDecode($binary, $mid, $max);

234         else

235             return $this->binDecode($binary, $min, $mid);

236     }

237 }

238

239

240

241

242

243

244 ?>

  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 }