php通过geohash算法实现查找附近的商铺

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。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基础类：

<?php

/**
 * Geohash generation class for php
 */
/**
 *
 * Encode and decode geohashes
 *
 * Find neighbors
 *
 */
class Geohash
{
    private $bitss = [16, 8, 4, 2, 1];
    private $neighbors = [];
    private $borders = [];

    private $coding = "0123456789bcdefghjkmnpqrstuvwxyz";
    private $codingMap = [];

    public function __construct()
    {

        $this->neighbors['right']['even'] = 'bc01fg45238967deuvhjyznpkmstqrwx';
        $this->neighbors['left']['even'] = '238967debc01fg45kmstqrwxuvhjyznp';
        $this->neighbors['top']['even'] = 'p0r21436x8zb9dcf5h7kjnmqesgutwvy';
        $this->neighbors['bottom']['even'] = '14365h7k9dcfesgujnmqp0r2twvyx8zb';

        $this->borders['right']['even'] = 'bcfguvyz';
        $this->borders['left']['even'] = '0145hjnp';
        $this->borders['top']['even'] = 'prxz';
        $this->borders['bottom']['even'] = '028b';

        $this->neighbors['bottom']['odd'] = $this->neighbors['left']['even'];
        $this->neighbors['top']['odd'] = $this->neighbors['right']['even'];
        $this->neighbors['left']['odd'] = $this->neighbors['bottom']['even'];
        $this->neighbors['right']['odd'] = $this->neighbors['top']['even'];

        $this->borders['bottom']['odd'] = $this->borders['left']['even'];
        $this->borders['top']['odd'] = $this->borders['right']['even'];
        $this->borders['left']['odd'] = $this->borders['bottom']['even'];
        $this->borders['right']['odd'] = $this->borders['top']['even'];

        //build map from encoding char to 0 padded bitfield
        for($i=0; $i<32; $i++) {
            $this->codingMap[substr($this->coding, $i, 1)] = str_pad(decbin($i), 5, "0", STR_PAD_LEFT);
        }

    }

    /**
     * Decode a geohash and return an array with decimal lat,long in it
     */
    public function decode($hash)
    {
        //decode hash into binary string
        $binary = "";
        $hl = strlen($hash);
        for ($i=0; $i<$hl; $i++) {

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

        //split the binary into lat and log binary strings
        $bl = strlen($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);
            }
        }

        //now concert to decimal
        $lat = $this->binDecode($blat, -90, 90);
        $long = $this->binDecode($blong, -180, 180);

        //figure out how precise the bit count makes this calculation
        $latErr = $this->calcError(strlen($blat), -90, 90);
        $longErr = $this->calcError(strlen($blong), -180, 180);

        //how many decimal places should we use? There's a little art to
        //this to ensure I get the same roundings as geohash.org
        $latPlaces = max(1, -round(log10($latErr))) - 1;
        $longPlaces = max(1, -round(log10($longErr))) - 1;

        //round it
        $lat = round($lat, $latPlaces);
        $long = round($long, $longPlaces);
        return array($lat, $long);
    }

    private function calculateAdjacent($srcHash, $dir)
    {
        $srcHash = strtolower($srcHash);
        $lastChr = $srcHash[strlen($srcHash) - 1];
        $type = (strlen($srcHash) % 2) ? 'odd' : 'even';
        $base = substr($srcHash, 0, strlen($srcHash) - 1);

        if (strpos($this->borders[$dir][$type], $lastChr) !== false) {
            $base = $this->calculateAdjacent($base, $dir);
        }

        return $base . $this->coding[strpos($this->neighbors[$dir][$type], $lastChr)];
    }

    public function neighbors($srcHash)
    {
        $geohashPrefix = substr($srcHash, 0, strlen($srcHash) - 1);

        $neighbors['top'] = $this->calculateAdjacent($srcHash, 'top');
        $neighbors['bottom'] = $this->calculateAdjacent($srcHash, 'bottom');
        $neighbors['right'] = $this->calculateAdjacent($srcHash, 'right');
        $neighbors['left'] = $this->calculateAdjacent($srcHash, 'left');

        $neighbors['topleft'] = $this->calculateAdjacent($neighbors['left'], 'top');
        $neighbors['topright'] = $this->calculateAdjacent($neighbors['right'], 'top');
        $neighbors['bottomright'] = $this->calculateAdjacent($neighbors['right'], 'bottom');
        $neighbors['bottomleft'] = $this->calculateAdjacent($neighbors['left'], 'bottom');

        return $neighbors;
    }

    /**
     * Encode a hash from given lat and long
     */
    public function encode($lat, $long)
    {
        //how many bits does latitude need?
        $plat = $this->precision($lat);
        $latbits = 1;
        $err = 45;
        while ($err > $plat) {
            $latbits++;
            $err /= 2;
        }

        //how many bits does longitude need?
        $plong = $this->precision($long);
        $longbits = 1;
        $err = 90;
        while ($err > $plong) {
            $longbits++;
            $err /= 2;
        }

        //bit counts need to be equal
        $bits = max($latbits, $longbits);

        //as the hash create bits in groups of 5, lets not
        //waste any bits - lets bulk it up to a multiple of 5
        //and favour the longitude for any odd bits
        $longbits = $bits;
        $latbits = $bits;
        $addlong = 1;
        while (($longbits + $latbits) % 5 != 0) {
            $longbits += $addlong;
            $latbits += !$addlong;
            $addlong = !$addlong;
        }

        //encode each as binary string
        $blat = $this->binEncode($lat, -90, 90, $latbits);
        $blong = $this->binEncode($long, -180, 180, $longbits);

        //merge lat and long together
        $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;
        }

        //convert binary string to hash
        $hash = "";
        for ($i=0; $i<strlen($binary); $i+=5) {
            $n = bindec(substr($binary, $i, 5));
            $hash = $hash.$this->coding[$n];
        }

        return $hash;
    }

    /**
     * What's the maximum error for $bits bits covering a range $min to $max
     */
    private function calcError($bits, $min, $max)
    {
        $err = ($max - $min) / 2;

        while ($bits--) {
            $err /= 2;
        }

        return $err;
    }

    /*
     * returns precision of number
     * precision of 42 is 0.5
     * precision of 42.4 is 0.05
     * precision of 42.41 is 0.005 etc
     *
     */
    private function precision($number)
    {
        $precision = 0;
        $pt = strpos($number,'.');
        if ($pt !== false) {
            $precision = -(strlen($number) - $pt - 1);
        }

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

    /**
     * create binary encoding of number as detailed in http://en.wikipedia.org/wiki/Geohash#Example
     * removing the tail recursion is left an exercise for the reader
     *
     * Author: Bruce Chen (weibo: @一个开发者)
     */
    private function binEncode($number, $min, $max, $bitcount)
    {
        if ($bitcount == 0) return "";

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

        //this is our mid point - we will produce a bit to say
        //whether $number is above or below this mid point
         $mid = ($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);
         }
    }

    /**
     * decodes binary encoding of number as detailed in http://en.wikipedia.org/wiki/Geohash#Example
     * removing the tail recursion is left an exercise for the reader
	 *
	 */
    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:

$geohash = new GeoHash();
$hash = $geohash->encode($latitude, $longitude);
//var_dump($hash);exit;
//决定查询范围，值越大，获取的范围越小
//当geohash base32编码长度为8时，精度在19米左右，而当编码长度为9时，精度在2米左右，编码长度需要根据数据情况进行选择。
$pre_hash = substr($hash, 0, 5);
//取出相邻八个区域
$neighbors = $geohash->neighbors($pre_hash);
array_push($neighbors, $pre_hash);

$values = '';
foreach ($neighbors as $key=>$val) {
$values .= '\'' . $val . '\'' .',';
}
$values = substr($values, 0, -1);
// var_dump($values);
$stores=\DB::select("SELECT * FROM `stores` WHERE LEFT(`geohash`,5) IN ($values)");

foreach ($stores as $key => $value) {
$geohash_arr=$geohash->decode($value->geohash);
$stores[$key]->latitude=$geohash_arr[0];//纬度
$stores[$key]->longitude=$geohash_arr[1];//经度
$distance=$this->getDistance($request['latitude'],$request['longitude'],$value->latitude,$value->longitude);
$stores[$key]->distance=$distance;
$sortdistance[$key] = $distance;
}
array_multisort($sortdistance,SORT_ASC,$stores);
// var_dump($stores);
return response()->json(['status_code'=>0,'nearby_stores'=>$stores]);

/**
* @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
}