我想在嵌入网页的google地图上实现轨迹显示，可是显示不了。应该怎么修改。请指点：

我想在google地图上实现轨迹代码如下，可是显示不了。应该怎么修改。请指点：<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
 <title>google地图 ——轨迹</title>
 <meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
 <script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=true"></script>
<script type="text/javascript">
        function initialize() {
            var myOptions = {
                zoom: 16,
                center: new google.maps.LatLng(39.964556,116.274834),
                mapTypeId: google.maps.MapTypeId.ROADMAP
            };
            var map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
            // 这里填上轨迹的经纬坐标,
    // 坐标做好是在路口的，不然画线不在路上。
            var trackPoints = [
                new google.maps.LatLng(39.964556,116.274834),
                new google.maps.LatLng(39.956662,116.275735),
                new google.maps.LatLng(39.957221,116.284447),
                new google.maps.LatLng(39.95834,116.29406),
                new google.maps.LatLng(39.959326,116.29951),
        new google.maps.LatLng(39.960083,116.303029),
        new google.maps.LatLng(39.96209,116.307793)
            ];
            
            var trackPath = new google.maps.Polyline({
                path: trackPoints,
                strokeColor: "#FF0000", // 线条颜色
                strokeOpacity: 1.0, // 线条透明度
                strokeWeight: 2 // 线条粗细
            });            trackPath.setMap(map);
        }</script>
</head>
<body onload="initialize()">
    <form id="form1" runat="server">
    <div id="map_canvas" style="width:100%; height:100%;"></div>
    </form>
</body>
</html>
怎么不显示要达到的预期效果