How to calculate the distance between two latitude and longitude using php

<strong>public function </strong>getdistanceAction()
{
    $lng1=117.27;  //经度1
    $lat1=31.86;   //纬度1
    $lng2=120.19;  //经度2
    $lat2=30.26;   //纬度2
    $EARTH_RADIUS = 6378137;   //地球半径
    $RAD = pi() / 180.0;
    $radLat1 = $lat1 * $RAD;
    $radLat2 = $lat2 * $RAD;
    $a = $radLat1 - $radLat2;    // 两点纬度差
    $b = ($lng1 - $lng2) * $RAD;  // 两点经度差
    $s = 2 * asin(sqrt(pow(sin($a / 2), 2) + cos($radLat1) * cos($radLat2) * pow(sin($b / 2), 2)));
    $s = $s * $EARTH_RADIUS;
    $s = round($s * 10000) / 10000;
    print_r($s);   //正确答案：330518.674
}