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航班飞行动画

发布于 2022-11-30 23:36:03 字数 6299 浏览 0 评论 0 收藏 0

本示例演示使用 ´postrender´ 来实现航班飞行动画。

本示例演示使用 postrender 和 vectorContext 实现航班飞行动画。使用 arc.js 计算两个机场之间的一个大的圆弧，然后使用 postrender 实现动画显示航班飞行路线。航班飞行数据由 OpenFlights（）提供。 The flight data is provided by OpenFlights (使用了来自 Mapbox.js文档的简化版数据集).

main.js

import 'ol/ol.css';
import Feature from 'ol/Feature';
import LineString from 'ol/geom/LineString';
import Map from 'ol/Map';
import Stamen from 'ol/source/Stamen';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';
import {Stroke, Style} from 'ol/style';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {getVectorContext} from 'ol/render';

const tileLayer = new TileLayer({
  source: new Stamen({
    layer: 'toner',
  }),
});

const map = new Map({
  layers: [tileLayer],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

const style = new Style({
  stroke: new Stroke({
    color: '#EAE911',
    width: 2,
  }),
});

const flightsSource = new VectorSource({
  wrapX: false,
  attributions:
    'Flight data by ' +
    '<a href="https://openflights.org/data.html">OpenFlights</a>,',
  loader: function () {
    const url = 'data/openflights/flights.json';
    fetch(url)
      .then(function (response) {
        return response.json();
      })
      .then(function (json) {
        const flightsData = json.flights;
        for (let i = 0; i < flightsData.length; i++) {
          const flight = flightsData[i];
          const from = flight[0];
          const to = flight[1];

          // create an arc circle between the two locations
          const arcGenerator = new arc.GreatCircle(
            {x: from[1], y: from[0]},
            {x: to[1], y: to[0]}
          );

          const arcLine = arcGenerator.Arc(100, {offset: 10});
          if (arcLine.geometries.length === 1) {
            const line = new LineString(arcLine.geometries[0].coords);
            line.transform('EPSG:4326', 'EPSG:3857');

            const feature = new Feature({
              geometry: line,
              finished: false,
            });
            // add the feature with a delay so that the animation
            // for all features does not start at the same time
            addLater(feature, i * 50);
          }
        }
        tileLayer.on('postrender', animateFlights);
      });
  },
});

const flightsLayer = new VectorLayer({
  source: flightsSource,
  style: function (feature) {
    // if the animation is still active for a feature, do not
    // render the feature with the layer style
    if (feature.get('finished')) {
      return style;
    } else {
      return null;
    }
  },
});

map.addLayer(flightsLayer);

const pointsPerMs = 0.1;
function animateFlights(event) {
  const vectorContext = getVectorContext(event);
  const frameState = event.frameState;
  vectorContext.setStyle(style);

  const features = flightsSource.getFeatures();
  for (let i = 0; i < features.length; i++) {
    const feature = features[i];
    if (!feature.get('finished')) {
      // only draw the lines for which the animation has not finished yet
      const coords = feature.getGeometry().getCoordinates();
      const elapsedTime = frameState.time - feature.get('start');
      const elapsedPoints = elapsedTime * pointsPerMs;

      if (elapsedPoints >= coords.length) {
        feature.set('finished', true);
      }

      const maxIndex = Math.min(elapsedPoints, coords.length);
      const currentLine = new LineString(coords.slice(0, maxIndex));

      // directly draw the line with the vector context
      vectorContext.drawGeometry(currentLine);
    }
  }
  // tell OpenLayers to continue the animation
  map.render();
}

function addLater(feature, timeout) {
  window.setTimeout(function () {
    feature.set('start', Date.now());
    flightsSource.addFeature(feature);
  }, timeout);
}

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Flight Animation</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep"></script>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="./resources/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,URL,TextDecoder,Number.isInteger"></script>
    <script src="https://api.mapbox.com/mapbox.js/plugins/arc.js/v0.1.0/arc.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "flight-animation",
  "dependencies": {
    "ol": "7.1.0"
  },
  "devDependencies": {
    "parcel": "^2.0.0-beta.1"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}

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