json绘制热力图

首先需要一段热力信息的json，我放在头部了。

然后就是需要de-geo库了。

实现代码如下：

    import * as d3geo from 'd3-geo'import trafficJSON from '../assets/json/traffic.json'let geoFun;// 地理投影函数// let info = {max: Number.MIN_SAFE_INTEGER,min: Number.MAX_SAFE_INTEGER,maxlng: Number.MIN_SAFE_INTEGER,minlng: Number.MAX_SAFE_INTEGER,maxlat: Number.MIN_SAFE_INTEGER,minlat: Number.MAX_SAFE_INTEGER,data: []};// 初始化地理投影const initGeo = (size) => {geoFun = d3geo.geoMercator().scale(size || 100)}// 经纬度转像素坐标const latlng2px = (pos) => {if (pos[0] >= -180 && pos[0] <= 180 && pos[1] >= -90 && pos[1] <= 90) {return geoFun(pos);}return pos;};// 创建颜色const createColors = (option) => {const canvas = document.createElement('canvas');document.body.appendChild(canvas);const ctx = canvas.getContext('2d');canvas.width = 256;canvas.height = 1;const grad = ctx.createLinearGradient(0, 0, canvas.width, canvas.height);for (let k in option.colors) {grad.addColorStop(k, option.colors[k]);}ctx.fillStyle = grad;ctx.fillRect(0, 0, canvas.width, canvas.height);return ctx.getImageData(0, 0, canvas.width, 1).data;}// 绘制圆const drawCircle = (ctx, option, item) => {let { lng, lat, value } = item;let x = lng - option.minlng + option.radius;let y = lat - option.minlat + option.radius;const grad = ctx.createRadialGradient(x, y, 0, x, y, option.radius);grad.addColorStop(0.0, 'rgba(0,0,0,1)');grad.addColorStop(1.0, 'rgba(0,0,0,0)');ctx.fillStyle = grad;ctx.beginPath();ctx.arc(x, y, option.radius, 0, 2 * Math.PI);ctx.closePath();ctx.globalAlpha = (value - option.min) / option.size;ctx.fill();}// 创建热力图const createHeatmap = (option) => {const canvas = document.createElement('canvas');document.body.appendChild(canvas);canvas.width = option.width;canvas.height = option.height;const ctx = canvas.getContext('2d');option.size = option.max - option.min;option.data.forEach((item) => {drawCircle(ctx, option, item);});const colorData = createColors(option);const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);for (let i = 3; i < imageData.data.length; i = i + 4) {let opacity = imageData.data[i];let offset = opacity * 4;//redimageData.data[i - 3] = colorData[offset];//greenimageData.data[i - 2] = colorData[offset + 1];//blueimageData.data[i - 1] = colorData[offset + 2];}ctx.putImageData(imageData, 0, 0);}// 初始化const init = () => {initGeo(1000)// 处理数据trafficJSON.features.forEach((item) => {let pos = latlng2px(item.geometry.coordinates);// 经纬度转像素坐标let newitem = {lng: pos[0],lat: pos[1],value: item.properties.avg}info.max = Math.max(newitem.value, info.max);info.maxlng = Math.max(newitem.lng, info.maxlng);info.maxlat = Math.max(newitem.lat, info.maxlat);info.min = Math.min(newitem.value, info.min);info.minlng = Math.min(newitem.lng, info.minlng);info.minlat = Math.min(newitem.lat, info.minlat);info.data.push(newitem);})info.size = info.max - info.min;info.sizelng = info.maxlng - info.minlng;info.sizelat = info.maxlat - info.minlat;const radius = 50;createHeatmap({width: info.sizelng + radius * 2,height: info.sizelng + radius * 2,colors: {0.1: '#2A85B8',0.2: '#16B0A9',0.3: '#29CF6F',0.4: '#5CE182',0.5: '#7DF675',0.6: '#FFF100',0.7: '#FAA53F',1: '#D04343'},radius,...info})}init();