ArcGIS JS 3.x使用webgl绘制热力图
ArcGIS Js Api 3.x 热力图在数据量达到三万左右的时候，绘制速度不尽人意，数据量再大些，缩放时候就会很卡，非常影响客户体验。
参考了一下网上webgl热力图，能达到更流畅的绘制的要求。(参考webgl-heatmap和heatmap-layer-js)webgl热力图使用很简单，只需要把屏幕坐标和权重设置到好就行，如下示例
heatmap.addPoints([{x:x, y:y, size:size, intensity:intensity}]);
依靠这个插件进行下热力图扩展，热力图插件和地图绑定首先要将地图坐标点转换出屏幕坐标就好了，设置好事件去联动请求数据。
var dataPoint = new Point(geo.x, geo.y, map.spatialReference);
screenGeometry = map.toScreen(dataPoint);
绑定好数据还要做的就是将热力图的画布元素放入合适位置(整好叠在地图上，尺寸一致)，不影响地图本身操作。
var canvas = document.getElementsByTagName('canvas')[0];
var heatmap = createWebGLHeatmap({
canvas: canvas,
intensityToAlpha: true
});
var reforeNode = document.getElementById("map_gc");
document.getElementById("map_layers").insertBefore(heatmap.canvas, reforeNode);
写好了扩展，生成十万的随机数据进行测试，与自带的热力图进行一下对比。自带热力图: 435.635ms；webgl热力图扩展：126.260ms。说明webgl速度更快，同时使用过程不存在地图卡顿，性能提升显著
附完整代码
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=7,IE=9"/>
<!--The viewport meta tag is used to improve the presentation and behavior
of the samples on iOS devices-->
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>heatmap.js ArcGIS JavaScript API Heatmap Layer</title>
<link rel="shortcut icon"
type="image/png" href="http://www.patrick-wied.at/img/favicon.png"/>
<link rel="stylesheet" href="https://js.arcgis.com/3.24/esri/css/esri.css">
<style>
body, html {
margin: 0;
padding: 0;
width: 99.9%;
height: 99.9%;
font-family: Arial;
}
#map {
width: 100%;
height: 100%;
margin: 0;
padding: 0;
border: 0px dashed black;
background-color: rgb(0, 38, 48);
}
</style>
</head>
<body>
<div id="map">
</div>
</body>
<script src="https://js.arcgis.com/3.24/"></script>
<script type="text/javascript" src="heatmap/webgl-heatmap.js"></script>
<script type="text/javascript">
var map;
require([
"esri/map",
"dojo/on",
"dojo/dom",
"esri/layers/ArcGISTiledMapServiceLayer",
"esri/tasks/query",
"esri/tasks/QueryTask",
"esri/geometry/screenUtils",
"esri/geometry/Extent",
"esri/geometry/Point",
"dojo/domReady!"
], function (
Map,
on,
dom,
ArcGISTiledMapServiceLayer,
Query,
QueryTask,
screenUtils,
Extent,
Point
) {
// Variables
var valueField = 'Focal'
// get the features within the current extent from the feature layer
function getFeatures() {
var q = new Query();
var url = 'http://services.arcgis.com/V6ZHFr6zdgNZuVG0/arcgis/rest/services/Earthquakes_Since_1970/FeatureServer/0'
var queryTask = new QueryTask(url);
q.geometry = map.extent;
q.where = "1=1";
q.outFields = [valueField ]
q.orderByFields = [valueField ];
q.returnGeometry = true
q.geometryPrecision = 10;
q.outSpatialReference = map.spatialReference;
queryTask.execute(q, function (re) {
console.log(re.features.length)
if (re.features.length) {
console.time('end')
console.log(re.features)
setdata(re.features);
console.timeEnd('end')
}
});
}
var mapExtent = new Extent({
xmax:22189975.059293926,
xmin: -15302081.56646192,
ymax: 8961447.604325403,
ymin: -9569334.036901515,
spatialReference: {wkid: 102100}
})
map = new Map("map", {
basemap: "gray",
extent: mapExtent,
sliderStyle: "small",
logo: false
});
map.resize();
var canvas = document.createElement('canvas');
canvas.id = "heatLayer";
canvas.style.zIndex = 99
canvas.style.position = "absolute";
canvas.style.width="100%"
canvas.style.height="100%"
var heatmap = createWebGLHeatmap({
canvas: canvas,
//gradientTexture: 'heatmap-gradient2.png',
intensityToAlpha: true
});
var reforeNode = document.getElementById("map_gc");
document.getElementById("map_layers").insertBefore(heatmap.canvas, reforeNode);
var raf = window.requestAnimationFrame || window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
var update = function () {
//heatmap.addPoint(100, 100, 100, 10/255);
heatmap.adjustSize(); // can be commented out for statically sized heatmaps, resize clears the map
heatmap.update(); // adds the buffered points
heatmap.display(); // adds the buffered points
raf(update);
}
raf(update);
//getFeatures()
getFeatures()
map.on('zoom-end', function (e) {
getFeatures()
});
map.on('zoom-start', function (e) {
heatmap.clear();
});
map.on('pan-start', function (e) {
heatmap.clear();
});
map.on('pan-end', getFeatures);
map.on('dragstart', function (e) {
heatmap.clear();
});
map.on('dragend', getFeatures);
map.on('mousewheel', function (e) {
heatmap.clear();
getFeatures()
})
function setdata(features) {
var i, da, m, dataPoint, heatmapdata, attributes, screenGeometry
heatmapdata = []
da = []
for (i = 0; i < features.length; i++) {
da.push();
}
m = features[features.length - 1].attributes[valueField ]
for (i = 0; i < features.length; i++) {
var geo = features[i].geometry.normalize();
dataPoint = new Point(geo.x, geo.y, map.spatialReference);
attributes = features[i].attributes;
var va = attributes[valueField ]
//var normalizedExtent = map.extent._normalize();
screenGeometry = map.toScreen(dataPoint);
//screenUtils.toScreenGeometry(normalizedExtent, map.width, map.height, dataPoint);
if (attributes && attributes.hasOwnProperty(valueField )) {
heatmapdata.push({
x: screenGeometry.x,
y: screenGeometry.y,
size: 30,
intensity: va / m
});
} else {
heatmapdata.push({
x: screenGeometry.x,
y: screenGeometry.y,
size: 30,
intensity: 0
});
}
}
heatmap.clear();
heatmap.addPoints(heatmapdata);
}
});
</script>
</html>
小贴士:开启大数据量绘制需要修改webgl-heatmap.js中的this.maxPointCount值(默认是10240),这样就可以为所欲为了。。。
