PHP 計算兩個經緯度的距離

/**
*求兩個已知經緯度之間的距離,單位為米
*@param lng1,lng2 經度
*@param lat1,lat2 緯度
*@return float 距離，單位米
*@author 
**/
function GetDistance($lat1, $lng1, $lat2, $lng2)
{
    $earthRadius = 6367000; //approximate radius of earth in meters
    $lat1 = ($lat1 * pi() ) / 180;
    $lng1 = ($lng1 * pi() ) / 180;

    $lat2 = ($lat2 * pi() ) / 180;
    $lng2 = ($lng2 * pi() ) / 180;

    $calcLongitude = $lng2 - $lng1;
    $calcLatitude = $lat2 - $lat1;
    $stepOne = pow(sin($calcLatitude / 2), 2) + cos($lat1) * cos($lat2) * pow(sin($calcLongitude / 2), 2);
    $stepTwo = 2 * asin(min(1, sqrt($stepOne)));
    $calculatedDistance = round($earthRadius * $stepTwo);

    return $calculatedDistance;
}