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 );

}