Maybe, you will be insituation when you need compute distance from two GPS coordinates (points).
So here is formula and PHP code:
$lat1=00.0000;
$lon1=00.0000;
$lat2=00.0000;
$lon2=00.0000;
$dlat = ($lat2-$lat1)*pi() / 180;
$dlon = ($lon2-$lon1)*pi() / 180;
$a= sin($dlat/2)*sin($dlat/2)+cos($lat1 * pi()/180) * cos($lat2 *pi()/180) * sin($dlon/2) * sin ($dlon/2);
$c=2 * atan2(sqrt($a),sqrt(1-$a));
$distance=6371000*$c;
echo round ($distance/1000,1) ;
