openlayers轨迹回放

  var vectorLayer, markers, lineFeature;
        var px, py;
        var x = 0;
        function startReplay() {
            //feature style
            var style_green = {
                strokeColor: "#339933",
                strokeOpacity: 1,
                strokeWidth: 3,
                pointRadius: 6,
                pointerEvents: "visiblePainted"
            };

            px = Math.random() * (122 - 121 + 0.001) + 121;
            py = Math.random() * (30 - 29 + 0.001) + 29;
            var lonlat = new OpenLayers.LonLat(px, py);
            var zoom = map.getZoom();
            map.setCenter(lonlat, zoom);

            vectorLayer = new OpenLayers.Layer.Vector("route");
            map.addLayer(vectorLayer);

            markers = new OpenLayers.Layer.Markers("marker");
            map.addLayer(markers);

            var imgUrl = "Images/car.png";
            var icon = new OpenLayers.Icon(imgUrl);
            var marker = new OpenLayers.Marker(lonlat, icon);
            markers.addMarker(marker);

            lineFeature = new OpenLayers.Feature.Vector(
                new OpenLayers.Geometry.LineString(lonlat.lon, lonlat.lat), null, style_green);
            vectorLayer.addFeatures([lineFeature]);

            fn();

        }

        function fn() {
            if (x < 20) {
                px = Math.random() * (122 - 121 + 0.001) + 121;
                py = Math.random() * (30 - 29 + 0.001) + 29;
                var lonlat = new OpenLayers.LonLat(px, py);
                var zoom = map.getZoom();
                map.setCenter(lonlat, zoom);

                var newPoint = new OpenLayers.Geometry.Point(lonlat.lon, lonlat.lat);
                lineFeature.geometry.addPoint(newPoint);
                vectorLayer.drawFeature(lineFeature);

                markers.clearMarkers();
                var imgUrl = "Images/car.png";
                var icon = new OpenLayers.Icon(imgUrl);
                var marker = new OpenLayers.Marker(lonlat, icon);
                markers.addMarker(marker);
                x++;
                setTimeout(fn, 1000);
            }
        }