Como atualizo os locais de vários marcadores no google maps

Estou usando a API do Google Maps para colocar marcadores em um mapa. As coordenadas gps dos marcadores são armazenadas em um banco de dados mySQL. Consegui criar os marcadores, no entanto, os locais mudavam constantemente, e eu estava pensando em como atualizar os locais dos marcadores para que os marcadores se movessem pelo mapa. Aqui esta o meu codigo ate agora

<!DOCTYPE html>
<html>
<head><title>Map</title>
<style type="text/css">
  html { height: 100% }
  body { height: 100%; margin: 0px; padding: 0px }
  #map_canvas { height: 100% }
</style>
<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false">
</script>
<script type="text/javascript">
  function initialize() {
    var latlng = new google.maps.LatLng(36.9947935, -122.0622702);
    var myOptions = {
        zoom: 15,
        center: latlng,
        mapTypeId: google.maps.MapTypeId.ROADMAP
    };
    var map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);



    var image = new google.maps.MarkerImage('busIcon.png',
        // The image size
        new google.maps.Size(44, 46),
        // The origin
        new google.maps.Point(0,0),
        // The anchor
        new google.maps.Point(22, 23));

    var shadow = new google.maps.MarkerImage('busIcon_shadow.png',
        new google.maps.Size(58, 46),
        new google.maps.Point(0,0),
        new google.maps.Point(22, 23)
    ); 

    var shape = {
        coord: [1, 1, 1, 45, 43, 45, 43 , 1],
        type: 'poly'
    };
    var markers = [

        <?php

        // Make a MySQL Connection
        mysql_connect("**********", "**********", "**********") or die(mysql_error());
        mysql_select_db("matsallen") or die(mysql_error());

        //Get number of rows
        $result = mysql_query
        (
            'SELECT COUNT(*) FROM busTrack AS count'
        )
        or die(mysql_error());

        $row = mysql_fetch_array( $result );

        $length = $row["COUNT(*)"];
        for ($count = 1; $count <= $length; $count++) {


            //Get data from MySQL database
            $result = mysql_query
            (
                'SELECT * FROM busTrack WHERE busID = '.$count
            )
            or die(mysql_error());




            // store the record of the "busTrack" table into $row
            $row = mysql_fetch_array( $result );

            // Echo the data into the array 'markers'

            $output = '{id: "Bus '.$row[busID].'", lat: '.$row[lat].', lng: '.$row[lon].'}';
            if ($count != $length) {
                $output = $output.',';
            };
            echo $output;
        };


        ?>

    ];

    for (index in markers) addMarker(map, markers[index]);



  function addMarker(map, data) {
    //create the markers
    var marker = new google.maps.Marker({
        position: new google.maps.LatLng(data.lat, data.lng),
        map: map,
        title: data.id,
        icon: image,
        shape: shape,
        shadow: shadow
    });

    //create the info windows
    var content = document.createElement("DIV");
    var title = document.createElement("DIV");
    title.innerHTML = data.id;
    content.appendChild(title);

    var infowindow = new google.maps.InfoWindow({
        content: content
    });

    // Open the infowindow on marker click
    google.maps.event.addListener(marker, "click", function() {
        infowindow.open(map, marker);
    });


  }
}



</script>
</head>
<body onload="initialize()">
  <div id="map_canvas" style="width:75%; height:75%; margin:10%; allign:center;"></div>
</body>
</html>

questionAnswers(1)

yourAnswerToTheQuestion