原文链接及内容

原文链接：https://openlayers.org/en/latest/examples/sea-level.html

运行界面

这个例子使用ol/source/Raster和Mapbox Terrain-RGB切片来“淹没”滑块上显示的海拔以下的区域。

main.js代码如下：

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import Map from 'ol/Map.js';
import View from 'ol/View.js';
import {Image as ImageLayer, Tile as TileLayer} from 'ol/layer.js';
import {Raster as RasterSource, XYZ} from 'ol/source.js';
import {fromLonLat} from 'ol/proj.js';

function flood(pixels, data) {
  const pixel = pixels[0];
  if (pixel[3]) {
    const height =
      -10000 + (pixel[0] * 256 * 256 + pixel[1] * 256 + pixel[2]) * 0.1;
    if (height <= data.level) {
      pixel[0] = 134;
      pixel[1] = 203;
      pixel[2] = 249;
      pixel[3] = 255;
    } else {
      pixel[3] = 0;
    }
  }
  return pixel;
}

const key = 'Get your own API key at https://www.maptiler.com/cloud/';
const attributions =
  '<a href="https://www.maptiler.com/copyright/" target="_blank">&copy; MapTiler</a> ' +
  '<a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap contributors</a>';

const elevation = new XYZ({
  // The RGB values in the source collectively represent elevation.
  // Interpolation of individual colors would produce incorrect evelations and is disabled.
  url: 'https://api.maptiler.com/tiles/terrain-rgb/{z}/{x}/{y}.png?key=' + key,
  tileSize: 512,
  maxZoom: 12,
  crossOrigin: '',
  interpolate: false,
});

const raster = new RasterSource({
  sources: [elevation],
  operation: flood,
});

const map = new Map({
  target: 'map',
  layers: [
    new TileLayer({
      source: new XYZ({
        attributions: attributions,
        url: 'https://api.maptiler.com/maps/streets/{z}/{x}/{y}.png?key=' + key,
        tileSize: 512,
        maxZoom: 22,
      }),
    }),
    new ImageLayer({
      opacity: 0.6,
      source: raster,
    }),
  ],
  view: new View({
    center: fromLonLat([-122.3267, 37.8377]),
    zoom: 11,
  }),
});

const control = document.getElementById('level');
const output = document.getElementById('output');
control.addEventListener('input', function () {
  output.innerText = control.value;
  raster.changed();
});
output.innerText = control.value;

raster.on('beforeoperations', function (event) {
  event.data.level = control.value;
});

const locations = document.getElementsByClassName('location');
for (let i = 0, ii = locations.length; i < ii; ++i) {
  locations[i].addEventListener('click', relocate);
}

function relocate(event) {
  const data = event.target.dataset;
  const view = map.getView();
  view.setCenter(fromLonLat(data.center.split(',').map(Number)));
  view.setZoom(Number(data.zoom));
}

界面布局文件index.html代码如下：

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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Sea Level</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      #level {
        display: inline-block;
        width: 150px;
        vertical-align: text-bottom;
      }

      a.location {
        cursor: pointer;
      }

      #map {
        background: #85ccf9;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <label>
      Sea level
      <input id="level" type="range" min="0" max="100" value="1"/>
      +<span id="output"></span> m
    </label>
    <br>
    Go to
    <a class="location" data-center="-122.3267,37.8377" data-zoom="11">San Francisco</a>,
    <a class="location" data-center="-73.9338,40.6861" data-zoom="11">New York</a>,
    <a class="location" data-center="72.9481,18.9929" data-zoom="11">Mumbai</a>, or
    <a class="location" data-center="120.831,31.160" data-zoom="9">Shanghai</a>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://cdn.jsdelivr.net/npm/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>