Haversine formula in PHP

Haversine PHP

function getDistance($latitude1, $longitude1, $latitude2, $longitude2) {
	$earth_radius = 6371000;
	
	$dLat = deg2rad($latitude2 - $latitude1);
	$dLon = deg2rad($longitude2 - $longitude1);
	
	$a = sin($dLat/2) * sin($dLat/2) + cos(deg2rad($latitude1)) * cos(deg2rad($latitude2)) * sin($dLon/2) * sin($dLon/2);
	$c = 2 * asin(sqrt($a));
	$d = $earth_radius * $c;
	
	return $d;
}