谷歌地图更新标记位置而不删除它们

我已经初始化了谷歌地图api v3，并使用setInterval重新加载xml标记列表，并将它们显示在地图上，因此我能够实时更新地图上的标记位置，甚至显示它们的移动。

这基本上是通过删除所有标记，然后在每次重新加载新数据时重新创建它们来实现的。

我想在这段代码中实现的是，而不是删除标记，更新它们的中毒，这应该有助于消除每次页面重新加载时的闪烁，我确实找到了其他答案，这些答案对我的具体做法没有帮助。

另一件事是，目前我正在根据某个课程值更改标记图标/图像，如下所示，我如何才能将其更改为具有多个条件，例如如果课程x=images=x.jpg（依此类推），我甚至想定义如果速度=x，那么图像xy.jpg，所以总共有两个问题。

 <script>
// COUNTER 
var k=1;
function myFunction()
{
setInterval(function(){
document.getElementById('spanSecond').innerHTML=10-k;
k++;
if(k>10){ k=1; timeout(); }
},1000);
}
myFunction();
var num=<?php echo $num;?>; 
// In the following example, markers appear when the user clicks on the map.
// The markers are stored in an array.
// The user can then click an option to hide, show or delete the markers.
var map;
var markers = [];
function initialize() {
  var haightAshbury = new google.maps.LatLng(<?php echo $cLat;?>, <?php echo $cLong; ?>);
  var mapOptions = {
    zoom: 5,
    center: haightAshbury,
    mapTypeId: google.maps.MapTypeId.ROADMAP
  };
  map = new google.maps.Map(document.getElementById('map-canvas'),
      mapOptions);

timeout();    
}

function timeout() { 

 downloadUrl("all__xml.php?UID=1", function(data) {
        var xml = data.responseXML;
        deleteMarkers();
        var markers = xml.documentElement.getElementsByTagName("marker");       
         for (var i = 0; i < markers.length; i++) { 
              var name = markers[i].getAttribute("name");
              var course = markers[i].getAttribute("course");
              var dt_image = markers[i].getAttribute("dt_image");
              var time = markers[i].getAttribute("deviceTime");
              var speed = markers[i].getAttribute("speed");
              var label = markers[i].getAttribute("deviceId");
              var tdiff = markers[i].getAttribute("tdiff");
            var Lat=parseFloat(markers[i].getAttribute("lat"));
            var Lng=parseFloat(markers[i].getAttribute("lng")); 
            var point = new google.maps.LatLng(Lat,Lng);
  if(tdiff>=2)
  { 
  var Acc="Off";
  speed=0; 
  }
  else var Acc="On"; 
  // data sending stop before 2 min => Acc off
  if(speed>1) {
  var status=Math.round(speed*1.852) + " moving"; 
  }
  else { 
  var status="stopped"; // moving status according to speed
  speed=0;
  }
  var html ='<div style="margin:1px !important; font-size:12px;">' + "<b>" + name + "</b> <br/>Angle : " + course + "<br/> Last Updated : " + time + "<br/> Acc : " + Acc + "<br/> Speed : " + Math.round(speed*1.852) + " kmph<br/>Lat : " + Lat + "<br/>Lng : " + Lng + "<br/>" + "<a href=tracking.php?DID=" + label + ">Tracking</a>" + " " + "<a href=playback.php?PlayBackDeviceId=" + label + "&Reset=1>Play Back</a>" + " " + "<a href=daily_distance_report.php?vehicle="+ label +">Reports</a>" + " " + "<a href=draw_geo_fence.php?deviceid="+ label+"&mapLat="+ Lat +"&mapLong="+ Lng +">Geo-Fence</a>"  + '</div>' ;
 //document.getElementById("status"+label).innerHTML=status; // show status in div tag

// Add a marker when click on the map
    addMarker(point,dt_image,course,html,name,i);
            }// loop end here     

   });   // downloadUrl end here 
}
// Add a marker to the map and push to the array.
function addMarker(location,image,course,html,name,i) {
    if(course<=22.5)
        {
            image = "images/"+image+"0.png"; // 0 angle img
        }
        else if (course<=67.5)
        {
            image = "images/"+image+"45.png"; // 45 angle img   
        }
        else if (course<=112.5)
        {
            image = "images/"+image+"90.png"; // 90 angle img   
        }
        else if (course<=157.5)
        {
            image = "images/"+image+"135.png"; // 135 angle img 
        }
        else if (course<=202.5)
        {
            image = "images/"+image+"180.png"; // 180 angle img 
        }       
        else if (course<=247.5)
        {
            image = "images/"+image+"225.png"; // 225 angle img 
        }
        else if (course<=292.5)
        {
            image = "images/"+image+"270.png"; // 270 angle img
        }       
        else
        {
            image = "images/"+image+"315.png"; // 315 angle img 
        }

  var marker = new MarkerWithLabel({
    position: location,
    icon:image,
    labelContent: name,
    labelAnchor: new google.maps.Point(22, 0),
    labelClass: "labels", // the CSS class for the label
    labelStyle: {opacity: 0.75},
    map: map    
  });
var infoWindow = new google.maps.InfoWindow({maxWidth:400});
google.maps.event.addListener(marker, 'click', function() {
        infoWindow.setContent(html);
        infoWindow.open(map, marker);
      });
markers.push(marker); 

}
// Sets the map on all markers in the array.
function setAllMap(map) {
  for (var i = 0; i < markers.length; i++) {
    markers[i].setMap(map);
    // Try update value here
  }
}
// Deletes all markers in the array by removing references to them.
function deleteMarkers() {
  setAllMap(null);
  markers = [];
}
google.maps.event.addDomListener(window, 'load', initialize);
    function downloadUrl(url, callback) {
      var request = window.ActiveXObject ?
          new ActiveXObject('Microsoft.XMLHTTP') :
          new XMLHttpRequest;
      request.onreadystatechange = function() {
        if (request.readyState == 4) {
          request.onreadystatechange = doNothing;
          callback(request, request.status);
        }
      };

      request.open('GET', url, true);
      request.send(null);
    }
    function doNothing() {}

///////////////////////////////////////////////////////////////
var geocoder = new google.maps.Geocoder();
//get geo location by name
function GetAddressByGoogle(t, lat, lng) {
    if (!geocoder) {
        geocoder = new google.maps.Geocoder();
    }
    if (lat != 0) {
        var latlng = new google.maps.LatLng(lat, lng);
        geocoder.geocode({ 'latLng': latlng }, function (results, status) {
            if (status == google.maps.GeocoderStatus.OK) {
                if (results[0]) {
            document.getElementById(t).innerHTML=results[0].formatted_address;
                }
            } 
        });
    }
}


</script>