openLayers地图缩放的回调

    //设置地图最小缩放级别为17级
     map.events.register("zoomend", this, function (e) {  
        //每次地图缩放时就会进入到这
        if (map.getZoom() < 17)
            {
                //map.zoomTo(17);
                map.setCenter(map.getCenter(),17);
            }
        });