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
}
