概述
在前文中，有一篇文章讲述了Openlayers2结合Echart实现地图统计图，还以一篇文章讲述了结合heatmap.js实现Openlayers中热力图的展示。在本文，书接前文，讲述Openlayers如何结合Echart实现热力图。
效果
全图效果
放大效果
实现
1、关键点
echart实现heatmap的关键点在与屏幕坐标，所以，在地图中，应通过地理坐标到屏幕坐标的转换函数，将地理坐标转换为屏幕坐标。
2、实现代码
我将热力图扩展成为了一个openlayers的layer扩展，实现代码如下：
OpenLayers.Layer.EchartHeatmap = OpenLayers.Class(OpenLayers.Layer,
{
isBaseLayer : false,
heatmap : null,
mapLayer : null,
heatdata : [],
initialize : function (name, map, options)
{
var scope = this, heatdiv = document.createElement("div"), handler;
OpenLayers.Layer.prototype.initialize.apply(this, [name, options]);
heatdiv.style.cssText = "position:absolute;" + map.size.w + "px;height:"
+ map.size.h + "px;";
this.div.appendChild(heatdiv);
this.map = map;
this.heatdiv = heatdiv;
this.heatdata = options.heatdata;
this.opacity = options.opacity;
handler = function (e)
{
if (scope.heatdata.length > 0)
{
scope.updateLayer(e);
}
};
handler();
map.events.register("zoomend", this, handler);
map.events.register("moveend", this, handler);
},
updateLayer : function (e)
{
var scope = this;
require(
[
'echarts',
'echarts/chart/heatmap'
],
function (ec)
{
var myChart = ec.init(scope.heatdiv);
var heatD = [];
var data = scope.heatdata;
var orgXy, w, h;
if(e){
orgXy = e.object.layerContainerOriginPx;
}
else{
orgXy={x:0,y:0};
}
w = scope.map.size.w;
h = scope.map.size.h;
scope.heatdiv.style.cssText = "position:absolute;top:"+(-orgXy.y)+"px;left:"+(-orgXy.x)+
"px;" + w + "px;height:" + h + "px;";
for (var i = 0; i < data.length; ++i)
{
var d = data[i];
var scrPt = scope.map.getPixelFromLonLat(new OpenLayers.LonLat(d.lon, d.lat));
var x = scrPt.x,
y = scrPt.y;
heatD.push([
x,
y,
d.count
]);
}
var option =
{
series : [
{
type : 'heatmap',
data : heatD,
opacity:scope.opacity,
gradientColors : [
{
offset : 0.4,
color : 'green'
},
{
offset : 0.5,
color : 'yellow'
},
{
offset : 0.8,
color : 'orange'
},
{
offset : 1,
color : 'red'
}
],
minAlpha : 0.2,
valueScale : 2
}
]
};
myChart.setOption(option);
});
},
destroy : function ()
{
OpenLayers.Layer.Grid.prototype.destroy.apply(this, arguments);
},
CLASS_NAME : "OpenLayers.Layer.EchartHeatmap"
}
);前台调用的代码如下：<html>
<head>
<meta charset="UTF-8">
<title>heatmap.js OpenLayers Heatmap Layer</title>
<link rel="stylesheet" href="../../../plugin/OpenLayers-2.13.1/theme/default/style.css" type="text/css">
<style>
html, body, #map,#chart{
padding:0;
margin:0;
height:100%;
100%;
overflow: hidden;
}
#chart{
position: absolute;
top: 0px;
left: 0px;
z-index: 900;
}
</style>
<script src="../../../plugin/OpenLayers-2.13.1/OpenLayers.js"></script>
<script src="../../../plugin/jquery/jquery-1.8.3.js"></script>
<script src="../../../plugin/echart/build/dist/echarts.js"></script>
<script src="extend/echartheatlayer.js"></script>
<script type="text/javascript">
require.config({
paths: {
echarts: '../../../plugin/echart/build/dist'
}
});
var map;
function init(){
var format = 'image/png';
var bounds = new OpenLayers.Bounds(
73.45100463562233, 18.16324718764174,
134.97679764650596, 53.531943152223576
);
var options = {
controls: [],
maxExtent: bounds,
maxResolution: 0.2403351289487642,
projection: "EPSG:4326",
units: 'degrees'
};
map = new OpenLayers.Map('map', options);
var wms1 = new OpenLayers.Layer.WMS("base_map",
"http://localhost:8088/geoserver/lzugis/wms",
{
layers: "province",
transparent: true
}, {
isBaseLayer: true,
singleTile: true
});
map.addControl(new OpenLayers.Control.Zoom());
map.addControl(new OpenLayers.Control.Navigation());
var heatmap = new OpenLayers.Layer.EchartHeatmap("heatmap",map,{
heatdata:data,
opacity:0.8
});
var wms2 = new OpenLayers.Layer.WMS("base_map",
"http://localhost:8088/geoserver/lzugis/wms",
{
layers: "county",
transparent: true
}, {
isBaseLayer: false,
singleTile: true,
opacity:0.2
});
map.addLayers([wms1,heatmap,wms2]);
map.zoomToExtent(bounds);
}
</script>
</head>
<body onload="init()">
<div id="map">
</div>
</body>
</html>其中，变量data的数据格式如下：[
{name:"东方市",lon:108.633357,lat:19.097025,count:30},
{name:"临高县",lon:109.686515,lat:19.91785,count:47},
{name:"儋州市",lon:109.575851,lat:19.518256,count:43},
{name:"昌江黎族自治县",lon:109.048657,lat:19.258351,count:71},
{name:"白沙黎族自治县",lon:109.448097,lat:19.235657,count:70},
……
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