PHP function calculate the distance between two coordinates (latitude, longitude)

function distance($lat1, $lng1, $lat2, $lng2, $miles = true)
{
$pi80 = M_PI / 180;
$lat1 *= $pi80;
$lng1 *= $pi80;
$lat2 *= $pi80;
$lng2 *= $pi80;

$r = 6372.797; // mean radius of Earth in km
$dlat = $lat2 – $lat1;
$dlng = $lng2 – $lng1;
$a = sin($dlat / 2) * sin($dlat / 2) + cos($lat1) * cos($lat2) * sin($dlng / 2) * sin($dlng / 2);
$c = 2 * atan2(sqrt($a), sqrt(1 – $a));
$km = $r * $c;

return ($miles ? ($km * 0.621371192) : $km);
}

PHP function calculate the distance between two coordinates (latitude, longitude)