vue利用openlayers实现动态轨迹

事件触发一个函数，这个事件本来是地图渲染结束事件，但是它的回调函数中，小车的坐标位置一直在变，那就会不停地触发地图渲染，当然最终也会触发。gis初学者可能对openlayers（后面简称ol）不熟悉，这里暂时不介绍ol了，直接上代码，先体验下感觉。这段代码有点难理解，最好自己尝试体验下，比较难理解部分我都加上了注释。线路有了，车也有了，现在就到了激动人心的开车时刻了，接下来才是本文最核心的代码！这

sinat_40572875

3455人浏览 · 2022-11-13 08:04:28

sinat_40572875 · 2022-11-13 08:04:28 发布

实现效果

今天介绍一个有趣的gis小功能：动态轨迹播放！效果就像这样：

这效果看着还很丝滑！别急，接下来教你怎么实现。代码示例基于parcel打包工具和es6语法，本文假设你已经掌握相关知识和技巧。

gis初学者可能对openlayers（后面简称ol）不熟悉，这里暂时不介绍ol了，直接上代码，先体验下感觉。

创建一个地图容器

引入地图相关对象

import Map from 'ol/Map';

import View from 'ol/View';

import XYZ from 'ol/source/XYZ';

import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';

创建地图对象

const center = [-5639523.95, -3501274.52];

const map = new Map({

target: document.getElementById('map'),

view: new View({

center: center,

zoom: 10,

minZoom: 2,

maxZoom: 19,

}),

layers: [

new TileLayer({

source: new XYZ({

attributions: attributions,

url: 'https://api.maptiler.com/maps/hybrid/{z}/{x}/{y}.jpg?key=' + key,

tileSize: 512,

}),

],

});

创建一条线路

画一条线路

可以用这个geojson网站随意画一条线，然后把数据内容复制下来，保存为json文件格式，作为图层数据添加到地图容器中。

你可以用异步加载的方式，也可以用require方式，这里都介绍下吧：

// fetch

fetch('data/route.json').then(function (response) {

response.json().then(function (result) {

const polyline = result.routes[0].geometry;

}),

};

// require

var roadData = require('data/route.json')

后面基本一样了，就以fetch为准，现在把线路加载的剩余部分补充完整：

fetch('data/route.json').then(function (response) {

response.json().then(function (result) {

const polyline = result.routes[0].geometry;

// 线路数据坐标系转换

const route = new Polyline({

factor: 1e6,

}).readGeometry(polyline, {

dataProjection: 'EPSG:4326',

featureProjection: 'EPSG:3857',

});

// 线路图层要素

const routeFeature = new Feature({

type: 'route',

geometry: route,

});

// 起点要素

const startMarker = new Feature({

type: 'icon',

geometry: new Point(route.getFirstCoordinate()),

});

// 终点要素

const endMarker = new Feature({

type: 'icon',

geometry: new Point(route.getLastCoordinate()),

});

// 取起点值

const position = startMarker.getGeometry().clone();

// 游标要素

const geoMarker = new Feature({

type: 'geoMarker',

geometry: position,

});

// 样式组合

const styles = {

// 路线

'route': new Style({

stroke: new Stroke({

width: 6,

color: [237, 212, 0, 0.8],

}),

'icon': new Style({

image: new Icon({

anchor: [0.5, 1],

src: 'data/icon.png',

}),

'geoMarker': new Style({

image: new CircleStyle({

radius: 7,

fill: new Fill({color: 'black'}),

stroke: new Stroke({

color: 'white',

width: 2,

}),

};

// 创建图层并添加以上要素集合

const vectorLayer = new VectorLayer({

source: new VectorSource({

features: [routeFeature, geoMarker, startMarker, endMarker],

}),

style: function (feature) {

return styles[feature.get('type')];

},

});

// 在地图容器中添加图层

map.addLayer(vectorLayer);

以上代码很完整，我加了注释，整体思路总结如下：

先加载路线数据
构造路线、起始点及游标对应图层要素对象
构造图层并把要素添加进去
在地图容器中添加图层

添加起、终点

这个上面的代码已经包括了，我这里列出来是为了让你更清晰，就是startMarker和endMarker对应的代码。

添加小车

同样的，这里的代码在上面也写过了，就是geoMarker所对应的代码。

准备开车

线路有了，车也有了，现在就到了激动人心的开车时刻了，接下来才是本文最核心的代码！

const speedInput = document.getElementById('speed');

const startButton = document.getElementById('start-animation');

let animating = false;

let distance = 0;

let lastTime;

function moveFeature(event) {

const speed = Number(speedInput.value);

// 获取当前渲染帧状态时刻

const time = event.frameState.time;

// 渲染时刻减去开始播放轨迹的时间

const elapsedTime = time - lastTime;

// 求得距离比

distance = (distance + (speed * elapsedTime) / 1e6) % 2;

// 刷新上一时刻

lastTime = time;

// 反减可实现反向运动，获取坐标点

const currentCoordinate = route.getCoordinateAt(

distance > 1 ? 2 - distance : distance

);

position.setCoordinates(currentCoordinate);

// 获取渲染图层的画布

const vectorContext = getVectorContext(event);

vectorContext.setStyle(styles.geoMarker);

vectorContext.drawGeometry(position);

map.render();

}

function startAnimation() {

animating = true;

lastTime = Date.now();

startButton.textContent = 'Stop Animation';

vectorLayer.on('postrender', moveFeature);

// 隐藏小车前一刻位置同时触发事件

geoMarker.setGeometry(null);

}

function stopAnimation() {

animating = false;

startButton.textContent = '开车了';

// 将小车固定在当前位置

geoMarker.setGeometry(position);

vectorLayer.un('postrender', moveFeature);

}

startButton.addEventListener('click', function () {

if (animating) {

stopAnimation();

} else {

startAnimation();

}

});

简单说下它的原理就是利用postrender事件触发一个函数，这个事件本来是地图渲染结束事件，但是它的回调函数中，小车的坐标位置一直在变，那就会不停地触发地图渲染，当然最终也会触发postrender。这样就实现的小车沿着轨迹的动画效果了。这段代码有点难理解，最好自己尝试体验下，比较难理解部分我都加上了注释。

好了，ol动态巡查已经介绍完了，动手试下吧！看你的车能否开起来？

完整代码

index.html

<!DOCTYPE html>

<html lang="en">

<head>

<meta charset="UTF-8">

<title>Marker Animation</title>

<script src="https://unpkg.com/elm-pep"></script>

<style>

.map {

width: 100%;

height:400px;

}

</style>

</head>

<body>

<div id="map" class="map"></div>

<label for="speed">

speed:

<input id="speed" type="range" min="10" max="999" step="10" value="60">

</label>

<button id="start-animation">Start Animation</button>

<script src="main.js"></script>

</body>

</html>

main.js

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import 'ol/ol.css';

import Feature from 'ol/Feature';

import Map from 'ol/Map';

import Point from 'ol/geom/Point';

import Polyline from 'ol/format/Polyline';

import VectorSource from 'ol/source/Vector';

import View from 'ol/View';

import XYZ from 'ol/source/XYZ';

import {

Circle as CircleStyle,

Fill,

Icon,

Stroke,

Style,

} from 'ol/style';

import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';

import {getVectorContext} from 'ol/render';

const key = 'Get your own API key at https://www.maptiler.com/cloud/';

const attributions =

'<a href="https://www.maptiler.com/copyright/" rel="external nofollow" target="_blank">© MapTiler</a> ' +

'<a href="https://www.openstreetmap.org/copyright" rel="external nofollow" target="_blank">© OpenStreetMap contributors</a>';

const center = [-5639523.95, -3501274.52];

const map = new Map({

target: document.getElementById('map'),

view: new View({

center: center,

zoom: 10,

minZoom: 2,

maxZoom: 19,

}),

layers: [

new TileLayer({

source: new XYZ({

attributions: attributions,

url: 'https://api.maptiler.com/maps/hybrid/{z}/{x}/{y}.jpg?key=' + key,

tileSize: 512,

}),

],

});

// The polyline string is read from a JSON similiar to those returned

// by directions APIs such as Openrouteservice and Mapbox.

fetch('data/polyline/route.json').then(function (response) {

response.json().then(function (result) {

const polyline = result.routes[0].geometry;

const route = new Polyline({

factor: 1e6,

}).readGeometry(polyline, {

dataProjection: 'EPSG:4326',

featureProjection: 'EPSG:3857',

});

const routeFeature = new Feature({

type: 'route',

geometry: route,

});

const startMarker = new Feature({

type: 'icon',

geometry: new Point(route.getFirstCoordinate()),

});

const endMarker = new Feature({

type: 'icon',

geometry: new Point(route.getLastCoordinate()),

});

const position = startMarker.getGeometry().clone();

const geoMarker = new Feature({

type: 'geoMarker',

geometry: position,

});

const styles = {

'route': new Style({

stroke: new Stroke({

width: 6,

color: [237, 212, 0, 0.8],

}),

'icon': new Style({

image: new Icon({

anchor: [0.5, 1],

src: 'data/icon.png',

}),

'geoMarker': new Style({

image: new CircleStyle({

radius: 7,

fill: new Fill({color: 'black'}),

stroke: new Stroke({

color: 'white',

width: 2,

}),

};

const vectorLayer = new VectorLayer({

source: new VectorSource({

features: [routeFeature, geoMarker, startMarker, endMarker],

}),

style: function (feature) {

return styles[feature.get('type')];

},

});

map.addLayer(vectorLayer);

const speedInput = document.getElementById('speed');

const startButton = document.getElementById('start-animation');

let animating = false;

let distance = 0;

let lastTime;

function moveFeature(event) {

const speed = Number(speedInput.value);

const time = event.frameState.time;

const elapsedTime = time - lastTime;

distance = (distance + (speed * elapsedTime) / 1e6) % 2;

lastTime = time;

const currentCoordinate = route.getCoordinateAt(

distance > 1 ? 2 - distance : distance

);

position.setCoordinates(currentCoordinate);

const vectorContext = getVectorContext(event);

vectorContext.setStyle(styles.geoMarker);

vectorContext.drawGeometry(position);

// tell OpenLayers to continue the postrender animation

map.render();

}

function startAnimation() {

animating = true;

lastTime = Date.now();

startButton.textContent = 'Stop Animation';

vectorLayer.on('postrender', moveFeature);

geoMarker.setGeometry(null);

}

function stopAnimation() {

animating = false;

startButton.textContent = '开车了';

geoMarker.setGeometry(position);

vectorLayer.un('postrender', moveFeature);

}

startButton.addEventListener('click', function () {

if (animating) {

stopAnimation();

} else {

startAnimation();

}

});

package.json

{

"name": "feature-move-animation",

"dependencies": {

"ol": "6.9.0"

},

"devDependencies": {

"parcel": "^2.0.0-beta.1"

},

"scripts": {

"start": "parcel index.html",

"build": "parcel build --public-url . index.html"

}

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