Extract data from Google Cal xml

Question

Extract data from Google Cal xml

I am getting an error while trying to extract some data from Google Cal using PHP. Here is the code:

$url = $_POST['url'];
$xml = file_get_contents($url);

$feed = simplexml_load_string($xml);
$ns= $feed->getNameSpaces(true);

foreach ($feed->entry as $entry) {
    $eventdetail = $entry->children($ns["gd"]);
    $when_atr = $eventdetail->when[0]->attributes();

    $title = $entry->title;
    echo "<div class='eventTitle'>".$title . "</div>";

    $where = $eventdetail->where[0]->attributes();
    echo "<div class='eventLocation'>" . $where . "</div>" . '<br />';

    $start = new DateTime($when_atr['startTime']);
    echo "<div class='eventTime'>".$start->format('D F jS, g:ia') . " to ";    

    $end = new DateTime($when_atr['endTime']);
    echo $end->format('g:ia')."</div>" . '<br />' ; 
}