OpenLayers地图比例尺控件实现详解

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
 <title></title>
 <script src="../lib/ol/ol.js"></script>
 <link href="../css/ol.css" rel="stylesheet" />
 <style type="text/css">
 #scalebar
 {
  float:left;
  margin-bottom:10px;
  z-index:2000;
 }
 </style>
 <script type="text/javascript">
 window.onload = function () {
  //实例化比例尺控件
  var scaleLineControl = new ol.control.ScaleLine({
  //设置度量单位为米
  units: 'metric',
  target: 'scalebar',
  className: 'ol-scale-line'
  });
  //实例化地图控件
  var map = new ol.Map({
  target: 'map',
  layers: [
   new ol.layer.Tile({
   source:new ol.source.OSM()
   }),
  ],
  view: new ol.View({
   center: [0, 0],
   zoom:2
  }),
  });
  //将比例尺控件加入到map中
  map.addControl(scaleLineControl);
 };
 </script>
</head>
<body>
 <div id="map"></div>
 <div id="scalebar"></div>
</body>
</html>