矢量图像图层

本示例演示将矢量数据渲染为图像图层.

本示例演示使用 ol/layer/VectorImage，可以在交互和动画过程中更快的渲染，但是会丢失精度。

main.js

import GeoJSON from 'ol/format/GeoJSON.js';
import Map from 'ol/Map.js';
import VectorImageLayer from 'ol/layer/VectorImage.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';
import {Fill, Stroke, Style} from 'ol/style.js';

const style = new Style({
  fill: new Fill({
    color: '#eeeeee',
  }),
});

const vectorLayer = new VectorImageLayer({
  background: '#1a2b39',
  imageRatio: 2,
  source: new VectorSource({
    url: 'https://openlayers.org/data/vector/ecoregions.json',
    format: new GeoJSON(),
  }),
  style: function (feature) {
    const color = feature.get('COLOR') || '#eeeeee';
    style.getFill().setColor(color);
    return style;
  },
});

const map = new Map({
  layers: [vectorLayer],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 1,
  }),
});

const featureOverlay = new VectorLayer({
  source: new VectorSource(),
  map: map,
  style: new Style({
    stroke: new Stroke({
      color: 'rgba(255, 255, 255, 0.7)',
      width: 2,
    }),
  }),
});

let highlight;
const displayFeatureInfo = function (pixel) {
  const feature = map.forEachFeatureAtPixel(pixel, function (feature) {
    return feature;
  });

  const info = document.getElementById('info');
  if (feature) {
    info.innerHTML = feature.get('ECO_NAME') || '&nbsp;';
  } else {
    info.innerHTML = '&nbsp;';
  }

  if (feature !== highlight) {
    if (highlight) {
      featureOverlay.getSource().removeFeature(highlight);
    }
    if (feature) {
      featureOverlay.getSource().addFeature(feature);
    }
    highlight = feature;
  }
};

map.on('pointermove', function (evt) {
  if (evt.dragging) {
    return;
  }
  const pixel = map.getEventPixel(evt.originalEvent);
  displayFeatureInfo(pixel);
});

map.on('click', function (evt) {
  displayFeatureInfo(evt.pixel);
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Vector Image Layer</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div id="info">&nbsp;</div>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="./resources/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "image-vector-layer",
  "dependencies": {
    "ol": "7.3.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}