PHP根据经纬度计算两点间实际距离

<?php
class CalculateUtil {
public static $EARTH_RADIUS = 6378.137;//地球半径
public static function rad($d)
{
return $d * pi() / 180.0;
}
/*
* $lat1 A点经度
* $lng1 A点维度
* $lat2 B点经度
* $lng2 B点经度
* return 两点间距离 单位KM
*/
public static function GetDistance($lat1, $lng1, $lat2, $lng2)
{
$radLat1 = self::rad($lat1);
$radLat2 = self::rad($lat2);
$a = $radLat1 - $radLat2;
$b = self::rad($lng1) - self::rad($lng2);

$s = 2 * asin(sqrt(pow(sin($a/2),2) +
cos($radLat1)*cos($radLat2)*pow(sin($b/2),2)));
$s = $s * self::$EARTH_RADIUS;
$s = round($s * 10000) / 10000;
return $s;
}
}