原文:
【百度地图API】如何利用自己的数据制作社交地图？只显示可视区域内的标注
摘要：如果你自己的数据已经超过1万个，如何进行合理的显示？除了聚合marker外，还有一个办法。那就是，只显示可视区域内的标注。
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成品图：
工具描述：
移动地图时（或改变地图级别时），只显示可视区域内的标注。非可视区域内的标注都移除。
这样可以保持高效的系统性能。
另外，可视区域内的标注，请保持在200以内。各类浏览器方能高效地显示。
如果有超过300个marker，建议使用聚合marker类，请参考LIB：http://dev.baidu.com/wiki/map/index.php?title=MapLibrary
1、从数据库里读取信息
数据库里需要存储的信息至少为：经纬度point，标注图片icon。
读取后，创建点、标注。（注意：只是创建标注，并不添加到地图上。）
//创建10个点
var p1 = new BMap.Point(116.387452,39.947302);
var p2 = new BMap.Point(116.361581,39.961129);
var p3 = new BMap.Point(116.437901,39.960133);
var p4 = new BMap.Point(116.459748,39.919528);
var p5 = new BMap.Point(116.424247,39.939557);
var p6 = new BMap.Point(116.485188,39.974511);
var p7 = new BMap.Point(116.485188,39.974511);
var p8 = new BMap.Point(116.494243,39.930484);
var p9 = new BMap.Point(116.45328,39.884103);
var p0 = new BMap.Point(116.456011,39.844671);
//创建10张图标
var icon1 = new BMap.Icon("img/1.jpg", new BMap.Size(50,50));
var icon2 = new BMap.Icon("img/2.jpg", new BMap.Size(50,50));
var icon3 = new BMap.Icon("img/3.jpg", new BMap.Size(50,50));
var icon4 = new BMap.Icon("img/4.jpg", new BMap.Size(50,50));
var icon5 = new BMap.Icon("img/5.jpg", new BMap.Size(50,50));
var icon6 = new BMap.Icon("img/6.jpg", new BMap.Size(50,50));
var icon7 = new BMap.Icon("img/7.jpg", new BMap.Size(50,50));
var icon8 = new BMap.Icon("img/8.jpg", new BMap.Size(50,50));
var icon9 = new BMap.Icon("img/9.jpg", new BMap.Size(50,50));
var icon0 = new BMap.Icon("img/0.jpg", new BMap.Size(50,50));
//创建10个marker，但不添加到地图上
var m1 = new BMap.Marker(p1,{icon:icon1});
var m2 = new BMap.Marker(p2,{icon:icon2});
var m3 = new BMap.Marker(p3,{icon:icon3});
var m4 = new BMap.Marker(p4,{icon:icon4});
var m5 = new BMap.Marker(p5,{icon:icon5});
var m6 = new BMap.Marker(p6,{icon:icon6});
var m7 = new BMap.Marker(p7,{icon:icon7});
var m8 = new BMap.Marker(p8,{icon:icon8});
var m9 = new BMap.Marker(p9,{icon:icon9});
var m0 = new BMap.Marker(p0,{icon:icon0});
为了方便运算，用一个数组将标注集合起来：
//建立一个marker的数组
var markers = [m1,m2,m3,m4,m5,m6,m7,m8,m9,m0,m11,m12,m13,m14,m15,m16,m17,m18,m19,m10,m21,m22,m23,m24,m25,m26,m27,m28,m29,m20];
2、判断标注是否在可视区域内
利用几何运算的LIB可以轻松判断，标注是否在可视区域内。
几何运算LIB：http://dev.baidu.com/wiki/map/index.php?title=MapLibrary
判断标注如果在可视区域内，则添加到地图上；如果标注不在可视区域内，则删除它。
判断代码：
//显示可视区域内的标注
function addMymarkers(){
for(i=0;i<markers.length;i++){
var result = BMapLib.GeoUtils.isPointInRect(markers[i].point, map.getBounds());
if(result == true) map.addOverlay(markers[i]);
else map.removeOverlay(markers[i]);
}
}
3、将可视区域内的标注添加到地图上
在图块加载完毕，地图中心点改变，和地图级别改变时，都需要进行一次添加/移除标注的操作。
//对地图级别变化、移动结束和图块加载完毕后，进行添加marker的操作
map.addEventListener("tilesloaded", addMymarkers);
map.addEventListener("zoomend", addMymarkers);
map.addEventListener("moveend", addMymarkers);
4、给标注的区域画一个框
为了方便观看，我用的是折线覆盖物，你也可以使用多边形覆盖物。
//添加一个矩形覆盖物
var polyline = new BMap.Polyline([
new BMap.Point(116.279655,40.020499),
new BMap.Point(116.260683,39.833259),
new BMap.Point(116.532043,39.830599),
new BMap.Point(116.526869,40.021383),
new BMap.Point(116.279655,40.020499)
], {strokeColor:"blue", strokeWeight:6, strokeOpacity:0.5});
map.addOverlay(polyline);
本例全部源代码：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>社交地图</title>
<script type="text/javascript" src="http://api.map.baidu.com/api?v=1.2"></script>
<script type="text/javascript" src="http://api.map.baidu.com/library/GeoUtils/1.2/src/GeoUtils_min.js"></script>
</head>
<body>
<div style="width:520px;height:340px;border:1px solid gray" id="container"></div>
<div style="width:200px;height:340px;border:1px solid gray" id="info"></div>
<p id="info"></p>
</body>
</html>
<script type="text/javascript">
//创建地图
var map = new BMap.Map("container");
map.centerAndZoom(new BMap.Point(116.387452,39.947302), 13);
//添加一个矩形覆盖物
var polyline = new BMap.Polyline([
new BMap.Point(116.279655,40.020499),
new BMap.Point(116.260683,39.833259),
new BMap.Point(116.532043,39.830599),
new BMap.Point(116.526869,40.021383),
new BMap.Point(116.279655,40.020499)
], {strokeColor:"blue", strokeWeight:6, strokeOpacity:0.5});
map.addOverlay(polyline);
//显示可视区域内的标注
function addMymarkers(){
document.getElementById("info").innerHTML = '';
for(i=0;i<markers.length;i++){
var result = BMapLib.GeoUtils.isPointInRect(markers[i].point, map.getBounds());
if(result == true) map.addOverlay(markers[i]);
else map.removeOverlay(markers[i]);
document.getElementById("info").innerHTML += '<img src="' + markers[i].getIcon().imageUrl +'" />';
}
}
//对地图级别变化、移动结束和图块加载完毕后，进行添加marker的操作
map.addEventListener("tilesloaded", addMymarkers);
map.addEventListener("zoomend", addMymarkers);
map.addEventListener("moveend", addMymarkers);
//创建30个点
var p1 = new BMap.Point(116.387452,39.947302);
var p2 = new BMap.Point(116.361581,39.961129);
var p3 = new BMap.Point(116.437901,39.960133);
var p4 = new BMap.Point(116.459748,39.919528);
var p5 = new BMap.Point(116.424247,39.939557);
var p6 = new BMap.Point(116.485188,39.974511);
var p7 = new BMap.Point(116.485188,39.974511);
var p8 = new BMap.Point(116.494243,39.930484);
var p9 = new BMap.Point(116.45328,39.884103);
var p0 = new BMap.Point(116.456011,39.844671);
var p11 = new BMap.Point(116.387165,39.850654);
var p12 = new BMap.Point(116.461185,39.8975);
var p13 = new BMap.Point(116.380122,39.87458);
var p14 = new BMap.Point(116.354395,39.899825);
var p15 = new BMap.Point(116.394495,39.887093);
var p16 = new BMap.Point(116.30524,39.902482);
var p17 = new BMap.Point(116.287992,39.937676);
var p18 = new BMap.Point(116.277931,39.911116);
var p19 = new BMap.Point(116.340166,39.929267);
var p10 = new BMap.Point(116.290004,39.965885);
var p21 = new BMap.Point(116.377535,39.966548);
var p22 = new BMap.Point(116.423672,39.95239);
var p23 = new BMap.Point(116.423672,39.95239);
var p24 = new BMap.Point(116.300353,40.003146);
var p25 = new BMap.Point(116.294172,39.982251);
var p26 = new BMap.Point(116.313432,39.977497);
var p27 = new BMap.Point(116.390183,39.983357);
var p28 = new BMap.Point(116.390183,39.983357);
var p29 = new BMap.Point(116.484469,39.943872);
var p20 = new BMap.Point(116.509191,39.932586);
//创建30张图标
var icon1 = new BMap.Icon("img/1.jpg", new BMap.Size(50,50));
var icon2 = new BMap.Icon("img/2.jpg", new BMap.Size(50,50));
var icon3 = new BMap.Icon("img/3.jpg", new BMap.Size(50,50));
var icon4 = new BMap.Icon("img/4.jpg", new BMap.Size(50,50));
var icon5 = new BMap.Icon("img/5.jpg", new BMap.Size(50,50));
var icon6 = new BMap.Icon("img/6.jpg", new BMap.Size(50,50));
var icon7 = new BMap.Icon("img/7.jpg", new BMap.Size(50,50));
var icon8 = new BMap.Icon("img/8.jpg", new BMap.Size(50,50));
var icon9 = new BMap.Icon("img/9.jpg", new BMap.Size(50,50));
var icon0 = new BMap.Icon("img/0.jpg", new BMap.Size(50,50));
var icon11 = new BMap.Icon("img/11.jpg", new BMap.Size(50,50));
var icon12 = new BMap.Icon("img/12.jpg", new BMap.Size(50,50));
var icon13 = new BMap.Icon("img/13.jpg", new BMap.Size(50,50));
var icon14 = new BMap.Icon("img/14.jpg", new BMap.Size(50,50));
var icon15 = new BMap.Icon("img/15.jpg", new BMap.Size(50,50));
var icon16 = new BMap.Icon("img/16.jpg", new BMap.Size(50,50));
var icon17 = new BMap.Icon("img/17.jpg", new BMap.Size(50,50));
var icon18 = new BMap.Icon("img/18.jpg", new BMap.Size(50,50));
var icon19 = new BMap.Icon("img/19.jpg", new BMap.Size(50,50));
var icon10 = new BMap.Icon("img/10.jpg", new BMap.Size(50,50));
var icon21 = new BMap.Icon("img/21.jpg", new BMap.Size(50,50));
var icon22 = new BMap.Icon("img/22.jpg", new BMap.Size(50,50));
var icon23 = new BMap.Icon("img/23.jpg", new BMap.Size(50,50));
var icon24 = new BMap.Icon("img/24.jpg", new BMap.Size(50,50));
var icon25 = new BMap.Icon("img/25.jpg", new BMap.Size(50,50));
var icon26 = new BMap.Icon("img/26.jpg", new BMap.Size(50,50));
var icon27 = new BMap.Icon("img/27.jpg", new BMap.Size(50,50));
var icon28 = new BMap.Icon("img/28.jpg", new BMap.Size(50,50));
var icon29 = new BMap.Icon("img/29.jpg", new BMap.Size(50,50));
var icon20 = new BMap.Icon("img/20.jpg", new BMap.Size(50,50));
//创建30个marker，但不添加到地图上
var m1 = new BMap.Marker(p1,{icon:icon1});
var m2 = new BMap.Marker(p2,{icon:icon2});
var m3 = new BMap.Marker(p3,{icon:icon3});
var m4 = new BMap.Marker(p4,{icon:icon4});
var m5 = new BMap.Marker(p5,{icon:icon5});
var m6 = new BMap.Marker(p6,{icon:icon6});
var m7 = new BMap.Marker(p7,{icon:icon7});
var m8 = new BMap.Marker(p8,{icon:icon8});
var m9 = new BMap.Marker(p9,{icon:icon9});
var m0 = new BMap.Marker(p0,{icon:icon0});
var m11 = new BMap.Marker(p11,{icon:icon11});
var m12 = new BMap.Marker(p12,{icon:icon12});
var m13 = new BMap.Marker(p13,{icon:icon13});
var m14 = new BMap.Marker(p14,{icon:icon14});
var m15 = new BMap.Marker(p15,{icon:icon15});
var m16 = new BMap.Marker(p16,{icon:icon16});
var m17 = new BMap.Marker(p17,{icon:icon17});
var m18 = new BMap.Marker(p18,{icon:icon18});
var m19 = new BMap.Marker(p19,{icon:icon19});
var m10 = new BMap.Marker(p10,{icon:icon10});
var m21 = new BMap.Marker(p21,{icon:icon21});
var m22 = new BMap.Marker(p22,{icon:icon22});
var m23 = new BMap.Marker(p23,{icon:icon23});
var m24 = new BMap.Marker(p24,{icon:icon24});
var m25 = new BMap.Marker(p25,{icon:icon25});
var m26 = new BMap.Marker(p26,{icon:icon26});
var m27 = new BMap.Marker(p27,{icon:icon27});
var m28 = new BMap.Marker(p28,{icon:icon28});
var m29 = new BMap.Marker(p29,{icon:icon29});
var m20 = new BMap.Marker(p20,{icon:icon20});
//建立一个marker的数组
var markers = [m1,m2,m3,m4,m5,m6,m7,m8,m9,m0,m11,m12,m13,m14,m15,m16,m17,m18,m19,m10,m21,m22,m23,m24,m25,m26,m27,m28,m29,m20];
</script>
2012-02-07 更新代码：修改addMymarkers函数。
当可视区域内的标注大于10的时候，只显示10个标注。并在右侧显示，可视区域内共有多少用户。
部分源代码：
//显示可视区域内的标注
function addMymarkers(){
document.getElementById("info").innerHTML = "小于10个用户";
var j = 0;
for(i=0;i<markers.length;i++){
var result = BMapLib.GeoUtils.isPointInRect(markers[i].point, map.getBounds());
if(result == true && j<10) {
map.addOverlay(markers[i]);
++j;
}
else if(result == true && j>=10){
++j;
document.getElementById("info").innerHTML = "可视区域内的用户数：</br><b style='color:red;font-size:50px'>" + j + "</b>";
map.removeOverlay(markers[i]);
}
else map.removeOverlay(markers[i]);
}
}
