How to access cck location field

I am trying to access the the location field in cck with a computed field. I am trying to use the script below. I am wanting to replace the hard coded lat=47 and lng=-122 with location fields.

$request_url = "http://ws.geonames.org/findNearbyPostalCodes?lat=47&lng=-122&maxRows=1";
$xml = simplexml_load_file($request_url) or die("feed not loading");

$zipcode = $xml->code->postalcode;


$node_field[0]['value'] =  $zipcode

I have tried without success

$node->locations[0]['latitude']['value']
$node->locations[0]['lat']['value']
$node->locations[0]['latitude']
$node->locations[0]['lat']
$node->locations['latitude']['value']
$node->locations['lat']['value']
$node->location[0]['latitude']['value']
$node->location[0]['lat']['value']
$node->location[0]['latitude']
$node->location[0]['lat']
$node->location['latitude']
$node->location['lat']

$locations[0]['latitude']['value']
$locations[0]['lat']['value']
$locations[0]['latitude']
$locations[0]['lat']
$locations['latitude']['value']
$locations['lat']['value']
$location[0]['latitude']['value']
$location[0]['lat']['value']
$location[0]['latitude']
$location[0]['lat']
$location['latitude']
$location['lat']