Calculate distance between points

This function will calculate the distance between point A (latitude, longitude) and point B (latitude, longitude) returning a distance in miles.

<?php function lat_long_dist($lat1, $long1, $lat2, $long2){
    $pi = pi();
    $x  = sin($lat1 * $pi/180) * 
          sin($lat2 * $pi/180) + 
          cos($lat1 * $pi/180) * 
          cos($lat2 * $pi/180) * 
          cos(($long2 * $pi/180) - ($long1 * $pi/180));
    $x  = atan((sqrt(1 - pow($x, 2))) / $x);
    return (1.852 * 60.0 * (($x/$pi) * 180)) / 1.609344;
}


echo lat_long_dist(56.34342, 49.324523, 57.49544, 47.421524);