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;
    }
}