[mapguide-users] What happens if the BBOX does not exist?

[=?gbk?B?vs+x8w==?=]

Why the 'BBOX' does not exist?If this happens,can I get the 'geometry'?
the codes is as following:
if (array_key_exists('BBOX', $_GET))
    {
        // split the client's BBOX return by commas and spaces to obtain an array of coordinates
        $coords = preg_split('/,|\s/', $_GET['BBOX']);
        $lowerLeft = $geometryFactory->CreateCoordinateXY($coords[0], $coords[1]);
        $upperRight = $geometryFactory->CreateCoordinateXY($coords[2], $coords[3]);

        $queryEnvelope = new MgEnvelope($lowerLeft, $upperRight);
    }

$featureService = $siteConnection->CreateService(MgServiceType::FeatureService);
    $queryOptions = new MgFeatureQueryOptions();

    $filter = urldecode($_GET["FILTER"]) ;
    //echo "<p>$filter</p>";
    echo '<Folder>';
    echo '<description>MapGuide - Wheaton Parcels Filtered ['.$filter.'] </description>';
    echo '<name>Wheaton Parcels</name>';
    echo '<visibility>0</visibility>';
    echo '<open>1</open>';

    $queryOptions->SetFilter($filter);
    //Feature Source being used in the application
    $featureReader = $featureService->SelectFeatures(new MgResourceIdentifier("Library://test/Data/province.FeatureSource"), "province", $queryOptions);
    //if($featureReader!=null) echo "<p>feature success!</p>";
    $geometryReaderWriter = new MgAgfReaderWriter();
    echo '<p>test1</p>';
    //Read Feature Source Attributes for populating Tooltip on Google Earth
    //Change this if using a different Feature Source
    $byteReader = $featureReader->GetGeometry('Geometry');
    //if($byteReader) echo '<p>feature success!</p>';
    $geometry = $geometryReaderWriter->Read($byteReader);
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/mapguide-users/attachments/20080528/80ec7401/attachment.html