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插值

disableimageinterpolation1 xyz7 maptiler25 reprojection8

Not Interpolated

Interpolated

本示例演示数据插值

本示例演示使用栅格 DEM（数字高程模型）数据的数据重采样。 interpolate: false 参数的设置，用于在重投影和渲染过程中，禁止数据插值。 高程数据是根据 forEachLayerAtPixel 返回的像素值计算的。 对比之下，在启动插值的第二个地图中很明显，在接近 3107 米的地方返回了不准确的高程数据。 这是因为高程数据是由像素值计算方式导致的。

main.js
import Map from 'ol/Map.js';
import TileLayer from 'ol/layer/Tile.js';
import View from 'ol/View.js';
import XYZ from 'ol/source/XYZ.js';

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 notInterpolated = new TileLayer({
  source: new XYZ({
    attributions: attributions,
    url:
      'https://api.maptiler.com/tiles/terrain-rgb/{z}/{x}/{y}.png?key=' + key,
    tileSize: 512,
    maxZoom: 12,
    crossOrigin: '',
    interpolate: false,
  }),
});

const interpolated = new TileLayer({
  source: new XYZ({
    attributions: attributions,
    url:
      'https://api.maptiler.com/tiles/terrain-rgb/{z}/{x}/{y}.png?key=' + key,
    tileSize: 512,
    maxZoom: 12,
    crossOrigin: '',
  }),
});

const view = new View({
  center: [6.893, 45.8295],
  zoom: 16,
  projection: 'EPSG:4326',
});

const map1 = new Map({
  target: 'map1',
  layers: [notInterpolated],
  view: view,
});

const map2 = new Map({
  target: 'map2',
  layers: [interpolated],
  view: view,
});

function getHeight(rgba) {
  return -10000 + (rgba[0] * 256 * 256 + rgba[1] * 256 + rgba[2]) * 0.1;
}

const info1 = document.getElementById('info1');
const info2 = document.getElementById('info2');
const showElevations = function (evt) {
  if (evt.dragging) {
    return;
  }
  const notInterpolatedPixel = notInterpolated.getData(evt.pixel);
  info1.innerText = notInterpolatedPixel
    ? getHeight(notInterpolatedPixel).toFixed(1)
    : '-';

  const interpolatedPixel = interpolated.getData(evt.pixel);
  info2.innerText = interpolatedPixel
    ? getHeight(interpolatedPixel).toFixed(1)
    : '-';
};

map1.on('pointermove', showElevations);
map2.on('pointermove', showElevations);
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Interpolation</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      @media (min-width: 800px) {
        .wrapper {
          display: flex;
        }
        .half {
          padding: 0 10px;
          width: 50%;
          float: left;
        }
      }
      #opacity {
        display: inline-block;
        width: 150px;
        vertical-align: text-bottom;
      }
    </style>
  </head>
  <body>
    <div class="wrapper">
      <div class="half">
        <h4>Not Interpolated</h4>
        <div id="map1" class="map"></div>
        <div>
          <label>
            Elevation
            <span id="info1">-</span> meters
          </label>
        </div>
      </div>
      <div class="half">
        <h4>Interpolated</h4>
        <div id="map2" class="map"></div>
        <div>
          <label>
            Elevation
            <span id="info2">-</span> meters
          </label>
        </div>
      </div>
    </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": "interpolation",
  "dependencies": {
    "ol": "7.3.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}