Google Maps API V3:简单标记群集未显示

我正在使用PHP，MongoDB，Javascript和Google Maps API V3开发基于Web的应用程序。

通过使用json_encode转换MongoDB数组，我能够在谷歌地图上轻松生成和显示标记。下面是带有标记和信息窗口的示例地图。

标记和信息窗口

但是，当我尝试实现Google Maps MarkerClusterer方法时，标记消失了。我遵循了Google Map的"A Simple MarkerClusterer Example"作为指南。

我还尝试声明一个全局集群对象，给它传递一个空数组，

var markerCluster = new MarkerClustrer(map, markers);

然后使用markerCluster.addMarkers(markers, true);作为替代方法，但没有运气。

这看起来很简单，但不知何故，它没有显示标记。我还尝试注释掉整个信息窗口/OnClick事件部分，因此我认为它与此无关。任何帮助将不胜感激。

PHP MongoDB 查询：

<?php
// Connect to Mongo and set DB and Collection
try
{
    $mongo = new Mongo();
    $db = $mongo->selectDB('twitter');
    $collection = $db->selectCollection('tweets');
}
catch(MongoConnectionException $e)
{
    die("Failed to connect to Twitter Database ". $e->getMessage());
}
// The hotspots array will contain the data that will be returned
$tweets = array();
// Return a cursor of tweets from MongoDB
$cursor = $collection->find();
// Try catch for catching whether there are tweets to display
$count = 0;
try 
{
    $count = $cursor->count();
} 
catch (MongoCursorException $e) 
{
    die(json_encode(array('error'=>'error message:' .$e->getMessage())));
}
// Loops through the cursor again specifically for querying all geo locations
// Unlike table display of tweets, this cursor is not limited by pages. 
foreach($cursor as $id => $value)
{ 
    $mapLocations[] = array
    (
        'id'=>$value['_id'],
        'screen_name'=>$value['screen_name'],
        'name'=>$value['name'],
        'tweet'=>$value['tweet'],
        'hashtags'=>$value['hashtags'],
        'lat'=>$value['geo']['lat'],
        'long'=>$value['geo']['long'],
        'date'=>$value['date'],
        'img'=>$value['img'],
        'specImg'=>$value['specImg']
    );
}
// var_dump($mapLocations);
?>

Javascript 函数：

function initialize() 
{
    // Converts MongoDB information to JSON, ready for Javascript
    var tweets = <?php echo json_encode($mapLocations); ?>;
    // Sets google maps options
    var myOptions = 
    {
        // Centers on Maui...
        center: new google.maps.LatLng(20.80362, -156.321716),
        zoom: 7,
        mapTypeId: google.maps.MapTypeId.TERRAIN
    };
    // Sets Marker Clusterer Options
    var mcOptions =
    {
        gridSize: 50, maxZoom: 15
    };
    // Generates Google Map and applies the defined options above.
    var map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
    // Infowindow for displaying information for onClick event  
    // Content must be inside the google.maps.event function 
    // Otherwise the same content will be entered on all markers    
    var infoWindow = new google.maps.InfoWindow({});
    var markerCluster = null;   // Initializes markerCluster
    var markers = [];           //Array needed to pass to MarkerClusterer
    // Loops through each tweet and draws the marker on the map.    
    for (var i = 0; i < tweets.length; i++)
    {
        var tweet = tweets[i];
        if(tweet.lat != null || tweet.long != null) 
        {
            var myLatLng = new google.maps.LatLng(tweet.lat, tweet.long);
            //document.write(" Latitude: " + tweet.lat + " Longitude: " + tweet.long + " <br> ");
            var marker = new google.maps.Marker({ 
                position: myLatLng,
                //icon: "markers/flag.png",
                //map: map,
            });
            markers.push(marker);
            google.maps.event.addListener(marker, 'click', (function(marker, i) 
            {
                return function() 
                {
                    // Generates a table for infoWindow
                    var content = "<table class='popup'>";
                    // Check if image exits, otherwise show no image icon
                    if(tweets[i].specImg != null) 
                    {
                        content += "<tr><th width=75 ><a href=" + tweets[i].specImg + ">";
                        content += "<img height=75 width=75 src=" + tweets[i].specImg + "></a>";
                    }
                    else
                    {
                        content += "<tr><th width=75><img height=75 width=75 src=images/noimage.jpg>";
                    }
                    // Concatanate screen name and tweet
                    // Will work on trimming information
                    content += "</th><td>" + tweets[i].screen_name + " says...<br>"; 
                    content += "''" + tweets[i].tweet +  "''<br>";
                    content += "on " + tweets[i].date + "</td>";
                    content += "</table>";
                    // Zoom into marker on click
                    map.setZoom(15);
                    map.setCenter(marker.getPosition());
                    // Sets the infoWindow content to the marker
                    infoWindow.setContent(content);
                    infoWindow.open(map, marker);
                }
            })(marker, i)); 
        }
    } 
    var markerCluster = new MarkerClusterer(map, markers);
}

@Robbie：

JSON $mapLocations变成了一个多维数组，但我简化了$mapLocations，只存储 2D 经度和经度。javascript源代码如下所示。

var tweets = [{"lat":20.87179594,"long":-156.47718775},{"lat":20.87195633,"long":-156.47714356},{"lat":20.87138419,"long":-156.47719744},{"lat":21.3320704,"long":-157.8685716},{"lat":null,"long":null},{"lat":21.36509415,"long":-157.92824454},{"lat":21.3320825,"long":-157.8684742},{"lat":null,"long":null},{"lat":21.33673131,"long":-157.86824},{"lat":21.332507,"long":-157.86635342},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":37.36520709,"long":-121.92386941},{"lat":37.2499758,"long":-121.86462506},{"lat":37.36278955,"long":-121.90521146},{"lat":null,"long":null},{"lat":37.36278955,"long":-121.90521146},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":20.88944108,"long":-156.4761887},{"lat":37.36273157,"long":-121.90479984},{"lat":20.85102618,"long":-156.65936351},{"lat":20.88949978,"long":-156.4762491},{"lat":null,"long":null},{"lat":21.3320168,"long":-157.8685715},{"lat":null,"long":null},{"lat":null,"long":null},{"lat":null,"long":null}];