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查寻附近网点geohash算法及实现 (PHP版本)

热度:74   发布时间:2016-04-28 18:06:53.0
查找附近网点geohash算法及实现 (PHP版本)

参考文档:

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

<?phpclass 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        http://en.wikipedia.org/wiki/Haversine_formula	   http://www.codecodex.com/wiki/Calculate_Distance_Between_Two_Points_on_a_Globe       验证:百度地图  http://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}  ?>