查找附近网点geohash算法及实现 （PHP版本）

https://blog.csdn.net/wangxiafghj/article/details/9014363geohash  算法原理及实现方式
https://blog.charlee.li/geohash-intro/  geohash：用字符串实现附近地点搜索
https://blog.sina.com.cn/s/blog_7c05385f0101eofb.html    查找附近点–Geohash方案讨论
https://www.wubiao.info/372        查找附近的xxx 球面距离以及Geohash方案探讨
https://en.wikipedia.org/wiki/Haversine_formula       Haversine formula球面距离公式
https://www.codecodex.com/wiki/Calculate_Distance_Between_Two_Points_on_a_Globe   球面距离公式代码实现
https://developer.baidu.com/map/jsdemo.htm#a6_1   球面距离公式验证  
https://www.wubiao.info/470     Mysql or Mongodb LBS快速实现方案

geohash有以下几个特点：

首先，geohash用一个字符串表示经度和纬度两个坐标。某些情况下无法在两列上同时应用索引 （例如MySQL 4之前的版本，Google App Engine的数据层等），利用geohash，只需在一列上应用索引即可。

其次，geohash表示的并不是一个点，而是一个矩形区域。比如编码wx4g0ec19，它表示的是一个矩形区域。 使用者可以发布地址编码，既能表明自己位于北海公园附近，又不至于暴露自己的精确坐标，有助于隐私保护。

第三，编码的前缀可以表示更大的区域。例如wx4g0ec1，它的前缀wx4g0e表示包含编码wx4g0ec1在内的更大范围。 这个特性可以用于附近地点搜索。首先根据用户当前坐标计算geohash（例如wx4g0ec1）然后取其前缀进行查询 （SELECT * FROM place WHERE geohash LIKE ‘wx4g0e%’），即可查询附近的所有地点。

Geohash比直接用经纬度的高效很多。

Geohash算法实现（PHP版本）

<?php class Geohash {     private $coding="0123456789bcdefghjkmnpqrstuvwxyz";     private $codingMap=array();        public function Geohash()     {         for($i=0; $i<32; $i++)         {             $this->codingMap[substr($this->coding,$i,1)]=str_pad(decbin($i), 5, "0", STR_PAD_LEFT);         }        }        public function decode($hash)     {         $binary="";         $hl=strlen($hash);         for($i=0; $i<$hl; $i++)         {             $binary.=$this->codingMap[substr($hash,$i,1)];         }            $bl=strlen($binary);         $blat="";         $blong="";         for ($i=0; $i<$bl; $i++)         {             if ($i%2)                 $blat=$blat.substr($binary,$i,1);             else                 $blong=$blong.substr($binary,$i,1);            }             $lat=$this->binDecode($blat,-90,90);          $long=$this->binDecode($blong,-180,180);         // $lat=$this->binDecode($blat,2,54);         // $long=$this->binDecode($blong,72,136);            $latErr=$this->calcError(strlen($blat),-90,90);         $longErr=$this->calcError(strlen($blong),-180,180);            $latPlaces=max(1, -round(log10($latErr))) - 1;         $longPlaces=max(1, -round(log10($longErr))) - 1;            $lat=round($lat, $latPlaces);         $long=round($long, $longPlaces);            return array($lat,$long);     }        public function encode($lat,$long)     {         $plat=$this->precision($lat);         $latbits=1;         $err=45;         while($err>$plat)         {             $latbits++;             $err/=2;         }            $plong=$this->precision($long);         $longbits=1;         $err=90;         while($err>$plong)         {             $longbits++;             $err/=2;         }            $bits=max($latbits,$longbits);            $longbits=$bits;         $latbits=$bits;         $addlong=1;         while (($longbits+$latbits)%5 != 0)         {             $longbits+=$addlong;             $latbits+=!$addlong;             $addlong=!$addlong;         }            $blat=$this->binEncode($lat,-90,90, $latbits);            $blong=$this->binEncode($long,-180,180,$longbits);            $binary="";         $uselong=1;         while (strlen($blat)+strlen($blong))         {             if ($uselong)             {                 $binary=$binary.substr($blong,0,1);                 $blong=substr($blong,1);             }             else             {                 $binary=$binary.substr($blat,0,1);                 $blat=substr($blat,1);             }             $uselong=!$uselong;         }            $hash="";         for ($i=0; $i<strlen($binary); $i+=5)         {             $n=bindec(substr($binary,$i,5));             $hash=$hash.$this->coding[$n];         }            return $hash;     }        private function calcError($bits,$min,$max)     {         $err=($max-$min)/2;         while ($bits--)             $err/=2;         return $err;     }        private function precision($number)     {         $precision=0;         $pt=strpos($number,'.');         if ($pt!==false)         {             $precision=-(strlen($number)-$pt-1);         }            return pow(10,$precision)/2;     }        private function binEncode($number, $min, $max, $bitcount)     {         if ($bitcount==0)             return "";         $mid=($min+$max)/2;         if ($number>$mid)             return "1".$this->binEncode($number, $mid, $max,$bitcount-1);         else             return "0".$this->binEncode($number, $min, $mid,$bitcount-1);     }        private function binDecode($binary, $min, $max)     {         $mid=($min+$max)/2;            if (strlen($binary)==0)             return $mid;            $bit=substr($binary,0,1);         $binary=substr($binary,1);            if ($bit==1)             return $this->binDecode($binary, $mid, $max);         else             return $this->binDecode($binary, $min, $mid);     } }    ?>

测试实例

<?php    require_once("db_config.php"); require_once('geohash.class.php');     $geohash=new Geohash;    //经纬度转换成Geohash    //获取附近的信息  $n_latitude  =  34.236080797698; $n_longitude = 109.0145193757;  echo "当前位置为：经度108.7455，纬度34.3608<br/><br/> 以下网点离我最近：";    //开始 $b_time = microtime(true);    //方案A，直接利用数据库存储函数，遍历排序    //方案B geohash求出附近，然后排序    //当前 geohash值  $n_geohash = $geohash->encode($n_latitude,$n_longitude);    //附近 $n = 3; $like_geohash = substr($n_geohash, 0, $n);   $sql = 'select * from retailersinfotable where geohash like "'.$like_geohash.'%"';      $query = mysql_query($sql);  if(mysql_num_rows($query))  {   while($row=mysql_fetch_array($query))   {    $data[] = array (        "latitude" =>$row["Latitude"],        "longitude"=>$row["Longitude"],        "name"     =>$row["RetailersName"],      );   } }    //算出实际距离  foreach($data as $key=>$val) {     $distance = getDistance($n_latitude,$n_longitude,$val['latitude'],$val['longitude']);     $data[$key]['distance'] = $distance;        //排序列     $sortdistance[$key] = $distance; }      //距离排序 array_multisort($sortdistance,SORT_ASC,$data);    //结束 $e_time = microtime(true);   echo "（计算耗时：" ; echo $e_time - $b_time;  echo "秒）<br/>";    //var_dump($data);     foreach($data as $key=>$val) {  echo "</br>";  echo $val['distance']. " 米-------".$val['name'];  }    /** *  @desc 根据两点间的经纬度计算距离 *  @param float $latitude 纬度值 *  @param float $longitude 经度值 */ function getDistance($latitude1, $longitude1, $latitude2, $longitude2)  {  $earth_radius = 6371000;   //approximate radius of earth in meters    $dLat = deg2rad($latitude2 - $latitude1);  $dLon = deg2rad($longitude2 - $longitude1);      /*        Using the        Haversine formula          https://en.wikipedia.org/wiki/Haversine_formula     https://www.codecodex.com/wiki/Calculate_Distance_Between_Two_Points_on_a_Globe        验证：百度地图  https://developer.baidu.com/map/jsdemo.htm#a6_1        calculate the distance      */   $a = sin($dLat/2) * sin($dLat/2) + cos(deg2rad($latitude1)) * cos(deg2rad($latitude2)) * sin($dLon/2) * sin($dLon/2);  $c = 2 * asin(sqrt($a));  $d = $earth_radius * $c;    return round($d);   //四舍五入 }    ?>