openlayers 学习笔记一

1. 创建地图，加载控件

var map = new OpenLayers.Map("map", {
  projection: new OpenLayers.Projection("EPSG:900913"),
  displayProjection: new OpenLayers.Projection("EPSG:4326")
});
map.addControl(new OpenLayers.Control.Permalink());
map.addControl(new OpenLayers.Control.MousePosition());

2.  创建世界范围的基于墨卡托投影的地图

var options = {
    projection: new OpenLayers.Projection("EPSG:900913"),//墨卡托投影
    units: "m",　　//以米为单位
    maxResolution: 156543.0339, //最大分辨率，0级 图上一个像素表示实际距离15万米多
    maxExtent: new OpenLayers.Bounds(-20037508.34, -20037508.34,20037508.34, 20037508.34) 
    //将地球分为4个卦象，156543.0339*128=20037508.34（为什么是*128，一个256*256的jpg中分，-128~128）
};

map = new OpenLayers.Map('map', options);

3. 坐标转换后居中 

 var proj = new OpenLayers.Projection("EPSG:4326");
 var point = new OpenLayers.LonLat(119,40);
 point.transform(proj, map.getProjectionObject());

 map.setCenter(point);//地理坐标 

 4. bounds 转换后居中

 var bounds = new OpenLayers.Bounds(-74.047185, 40.679648, -73.907005, 40.882078);
 bounds.transform(proj, map.getProjectionObject());

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