function NavigationTool() {

           var mode = google.maps.DirectionsTravelMode.DRIVING; //谷歌地图路线指引的模式

           var directionsDisplay = new google.maps.DirectionsRenderer();   //地图路线显示对象

           var directionsService = new google.maps.DirectionsService();    //地图路线服务对象

           var directionsVisible = false;  //是否显示路线

           directionsDisplay.setMap(null);

           directionsDisplay.setMap(map);

           var Navigpoints = []; //起终点

           google.maps.event.addListener(map, "click", function(evt) {

               if (Navigpoints.length == 0) {

                   if (confirm("是否将当前点设为起点？")) {

                       Navigpoints.push(evt.latLng);

                   }

               } else {

                   if (Navigpoints.length >= 2) { points = []; google.maps.event.clearListeners(map, "click"); return; }

                   if (confirm("是否将当前点设为终点？")) {

                       Navigpoints.push(evt.latLng);

                       var request = {

                           origin: Navigpoints[0], //起点

                           destination: Navigpoints[1], //终点

                           travelMode: mode,

                           optimizeWaypoints: true,

                           avoidHighways: false,

                           avoidTolls: false

                       };

                       directionsService.route(

                        request,

                        function(response, status) {

                            if (status == google.maps.DirectionsStatus.OK) {

                                directionsDisplay.setDirections(response);

                                //定时清除线路

                                setTimeout(function() { directionsDisplay.setMap(null) }, 8000);

                            }

                        }

                    );

                   }

               }

           });

           directionsVisible = true;

       }