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vue利用openlayers实现动态轨迹

字节逆旅 人气:0

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：

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>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <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

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">&copy; MapTiler</a> ' +
  '<a href="https://www.openstreetmap.org/copyright" rel="external nofollow"  target="_blank">&copy; 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"
  }
}

参考资源：

https://openlayers.org/en/latest/examples/feature-move-animation.html

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