标签：des style blog http ar io color os 使用
参考文档：
http://blog.csdn.net/wangxiafghj/article/details/9014363geohash 算法原理及实现方式
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);
}
}
?><?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
}
?>
标签：des style blog http ar io color os 使用
原文地址：http://blog.csdn.net/sunrise_2013/article/details/42024507
