GeoTIFF tile pyramid

Rendering a COG tile pyramid as layer group.

Data from a Cloud Optimized GeoTIFF (COG) tile pyramid can be rendered as a set of layers. In this example, a pyramid of 3-band GeoTIFFs is used to render RGB data. For each tile of the pyramid, a separate layer is created on demand. The lowest resolution layer serves as preview while higher resolutions are loading.

main.js

import 'ol/ol.css';
import GeoTIFF from 'ol/source/GeoTIFF';
import LayerGroup from 'ol/layer/Group';
import Map from 'ol/Map';
import TileGrid from 'ol/tilegrid/TileGrid';
import View from 'ol/View';
import WebGLTileLayer from 'ol/layer/WebGLTile';
import {getIntersection} from 'ol/extent';

// Metadata from https://s2downloads.eox.at/demo/EOxCloudless/2019/rgb/2019_EOxCloudless_rgb.json

// Tile grid of the GeoTIFF pyramid layout
const tileGrid = new TileGrid({
  origin: [-180, 90],
  resolutions: [0.703125, 0.3515625, 0.17578125, 8.7890625e-2, 4.39453125e-2],
  tileSizes: [
    [512, 256],
    [1024, 512],
    [2048, 1024],
    [4096, 2048],
    [4096, 4096],
  ],
});

const pyramid = new LayerGroup();
const layerForUrl = {};
const zs = tileGrid.getResolutions().length;

function useLayer(z, x, y) {
  const url = `https://s2downloads.eox.at/demo/EOxCloudless/2019/rgb/${z}/${y}/${x}.tif`;
  if (!(url in layerForUrl)) {
    pyramid.getLayers().push(
      new WebGLTileLayer({
        minZoom: z,
        maxZoom: z === 0 || z === zs - 1 ? undefined : z + 1,
        extent: tileGrid.getTileCoordExtent([z, x, y]),
        source: new GeoTIFF({
          sources: [
            {
              url: url,
            },
          ],
        }),
      })
    );
    layerForUrl[url] = true;
  }
}

const map = new Map({
  target: 'map',
  layers: [pyramid],
  view: new View({
    projection: 'EPSG:4326',
    center: [0, 0],
    zoom: 0,
    showFullExtent: true,
  }),
});

// Add overview layer
useLayer(0, 0, 0);

// Add layer for specific extent on demand
map.on('moveend', () => {
  const view = map.getView();
  tileGrid.forEachTileCoord(
    getIntersection([-180, -90, 180, 90], view.calculateExtent()),
    tileGrid.getZForResolution(view.getResolution()),
    ([z, x, y]) => useLayer(z, x, y)
  );
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>GeoTIFF tile pyramid</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep"></script>
    <!-- The lines below are only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.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": "cog-pyramid",
  "dependencies": {
    "ol": "6.12.0"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}