Calculate Distance by Latitude and Longitude

function calcDistance($userLat, $userLon) {
	$storeLat = ;
	$storeLon = ;
	$radlat1 = pi() * $userLat / 180;
	$radlat2 = pi() * $storeLat / 180;
	$radlon1 = pi() * $userLon / 180;
	$radlon2 = pi() * $storeLon / 180;
	$theta = $userLat - $storeLat;
	$radtheta = pi() * $theta / 180;

	$dist = sin($radlat1) * sin($radlat2) + cos($radlat1) * cos($radlat2) * cos($radtheta);
	$dist = acos($dist);
	$dist = $dist * 180 / pi();
	$dist = $dist * 60 * 1.1515;
	$dist = $dist / 10;

	return $dist;
}