分析 Earthquakes Heatmap 这个 demo，官网介绍是：
This example parses a KML file and renders the features as a ol/layer/Heatmap layer.
这个示例解析了 KML 格式文件并作为一个热力图来渲染要素。
定义基本结构
这个示例比较简单，地图的基本结构如下所示，raster 图层使用的是普通的 toner 碳粉地图， vector 矢量图层的定义见下节。在 DOM 中，添加两个 range 类型的 input 标签，用于控制热力图的属性。
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| <!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<link
rel="stylesheet"
href="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.1.1/css/ol.css"
type="text/css"
/>
<script src="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.1.1/build/ol.js"></script>
<title>Earthquakes Heatmap(地震热力图)</title>
<style>
html,
body,
.map {
height: 100%;
width: 100%;
}
</style>
</head>
<body>
<form>
<label>半径大小</label>
<input id="radius" type="range" min="1" max="50" step="1" value="5" />
<label>模糊大小</label>
<input id="blur" type="range" min="1" max="50" step="1" value="15" />
</form>
<div id="map" class="map"></div>
<script type="text/javascript">
let raster = new ol.layer.Tile({
source: new ol.source.Stamen({
layer: "toner"
})
});
let map = new ol.Map({
layers: [raster, vector],
target: "map",
view: new ol.View({
center: [0, 0],
zoom: 2
})
});
</script>
</body>
</html>
|
Heatmap 矢量图层
关于 ol.layer.Heatmap 对象的API如下图所示：
除了 source 属性外，设置热力图最关键的几个属性是 blur（热力圆圈的模糊大小）、radius（热力圆圈的半径），还有一个 weight 权重属性。weight 属性是一个回调函数，入参是 feature 要素，返回的结果应该是一个范围为[0, 1]的的权重值，权重越大就越热。
blur 和 radius 取得是两个 input 标签中的值。source 属性中的ol.layer.Vector读取的是 KML 格式的 2012 年世界 5 级地震数据，所以所有的震级都是五点几，减去 5 后，自然会返回一个[0, 1]的的权重值。
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|
let blur = document.getElementById("blur");
let radius = document.getElementById("radius");
let vector = new ol.layer.Heatmap({
source: new ol.source.Vector({
url:
"https://openlayers.org/en/latest/examples/data/kml/2012_Earthquakes_Mag5.kml",
format: new ol.format.KML({
extractStyles: false
})
}),
blur: parseInt(blur.value, 10),
radius: parseInt(radius.value, 10),
weight: feature => {
let name = feature.get("name");
let magnitude = parseFloat(name.substr(2));
return magnitude - 5;
}
});
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事件绑定
这里就是普通的事件回调，给两个 input 标签设置两个 input 和 change 事件绑定，触发时就会调用setBlur和setRadius方法给 Heatmap 设置 blur 和 radius 值，并同步到地图中。
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let blurHandler = () => {
vector.setBlur(parseInt(blur.value, 10));
};
blur.addEventListener("input", blurHandler);
blur.addEventListener("change", blurHandler);
let radiusHandler = () => {
vector.setRadius(parseInt(radius.value, 10));
};
radius.addEventListener("input", radiusHandler);
radius.addEventListener("change", radiusHandler);
|
全部代码
全部代码如下：
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| <!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<link
rel="stylesheet"
href="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.1.1/css/ol.css"
type="text/css"
/>
<script src="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.1.1/build/ol.js"></script>
<title>Earthquakes Heatmap(地震热力图)</title>
<style>
html,
body,
.map {
height: 100%;
width: 100%;
}
</style>
</head>
<body>
<form>
<label>半径大小</label>
<input id="radius" type="range" min="1" max="50" step="1" value="5" />
<label>模糊大小</label>
<input id="blur" type="range" min="1" max="50" step="1" value="15" />
</form>
<div id="map" class="map"></div>
<script type="text/javascript">
let blur = document.getElementById("blur");
let radius = document.getElementById("radius");
let vector = new ol.layer.Heatmap({
source: new ol.source.Vector({
url:
"https://openlayers.org/en/latest/examples/data/kml/2012_Earthquakes_Mag5.kml",
format: new ol.format.KML({
extractStyles: false
})
}),
blur: parseInt(blur.value, 10),
radius: parseInt(radius.value, 10),
weight: feature => {
let name = feature.get("name");
let magnitude = parseFloat(name.substr(2));
return magnitude - 5;
}
});
let raster = new ol.layer.Tile({
source: new ol.source.Stamen({
layer: "toner"
})
});
let map = new ol.Map({
layers: [raster, vector],
target: "map",
view: new ol.View({
center: [0, 0],
zoom: 2
})
});
let blurHandler = () => {
vector.setBlur(parseInt(blur.value, 10));
};
blur.addEventListener("input", blurHandler);
blur.addEventListener("change", blurHandler);
let radiusHandler = () => {
vector.setRadius(parseInt(radius.value, 10));
};
radius.addEventListener("input", radiusHandler);
radius.addEventListener("change", radiusHandler);
</script>
</body>
</html>
|
