已知两点的坐标，我要怎样返回两点间的交通线路？

[miya tang]

   <script type="text/javascript"> 
	// Create a directions object and register a map and DIV to hold the 

    // resulting computed directions

    var map;
    var directionsPanel;
    var directions;

    function initialize() {
      map = new GMap2(document.getElementById("map_canvas"));

      map.setCenter(new GLatLng(42.351505,-71.094455), 15);
      directionsPanel = document.getElementById("route");
      directions = new GDirections(map, directionsPanel);
      directions.load("from: 500 Memorial Drive, Cambridge, MA to: 4 Yawkey Way, Boston, MA 02215 (Fenway Park)", {travelMode:G_TRAVEL_MODE_WALKING});

    }
    </script>

以上是GOOGLE 交通线路的示例代码，看到
directions.load　里面，只能传入两个地址名称．但我已知道出发点，和目的地的坐标点．就应该是传入坐标就可以吧．
要怎样来实现？

请各位高手指点．