PHP: Calcula distancias pela latitude e longitude

Calcula distancias pela latitude e longitude

/*
 * Calcula distancias
 */
function distance($lat1, $lon1, $lat2, $lon2, $unit) {

	$theta = $lon1 - $lon2;
	$dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
	$dist = acos($dist);
	$dist = rad2deg($dist);
	$miles = $dist * 60 * 1.1515;
	$unit = strtoupper($unit);

	if ($unit == "K")
		return ($miles * 1.609344);
	else if ($unit == "N")
		return ($miles * 0.8684);
	else
		return $miles;
}