WMTS Tile Transitions

Sea-level

Example of smooth tile transitions when changing the dimension of a WMTS layer.

Demonstrates smooth reloading of layers when changing a dimension continuously. The demonstration layer is a global sea-level computation (flooding computation from SCALGO, underlying data from CGIAR-CSI SRTM) where cells that are flooded if the sea-level rises to more than x m are colored blue. The user selects the sea-level dimension using a slider.

main.js

import Map from 'ol/Map.js';
import OSM from 'ol/source/OSM.js';
import TileLayer from 'ol/layer/Tile.js';
import View from 'ol/View.js';
import WMTS from 'ol/source/WMTS.js';
import WMTSTileGrid from 'ol/tilegrid/WMTS.js';
import {get as getProjection} from 'ol/proj.js';
import {getTopLeft, getWidth} from 'ol/extent.js';

// create the WMTS tile grid in the google projection
const projection = getProjection('EPSG:3857');
const tileSizePixels = 256;
const tileSizeMtrs = getWidth(projection.getExtent()) / tileSizePixels;
const matrixIds = [];
const resolutions = [];
for (let i = 0; i <= 14; i++) {
  matrixIds[i] = i;
  resolutions[i] = tileSizeMtrs / Math.pow(2, i);
}
const tileGrid = new WMTSTileGrid({
  origin: getTopLeft(projection.getExtent()),
  resolutions: resolutions,
  matrixIds: matrixIds,
});

const scalgoToken = 'CC5BF28A7D96B320C7DFBFD1236B5BEB';

const wmtsSource = new WMTS({
  url: 'https://ts2.scalgo.com/olpatch/wmts?token=' + scalgoToken,
  layer: 'SRTM_4_1:SRTM_4_1_flooded_sealevels',
  format: 'image/png',
  matrixSet: 'EPSG:3857',
  attributions: [
    '<a href="https://scalgo.com" target="_blank">SCALGO</a>',
    '<a href="https://cgiarcsi.community/data/' +
      'srtm-90m-digital-elevation-database-v4-1"' +
      ' target="_blank">CGIAR-CSI SRTM</a>',
  ],
  tileGrid: tileGrid,
  style: 'default',
  dimensions: {
    'threshold': 100,
  },
});

const map = new Map({
  target: 'map',
  view: new View({
    projection: projection,
    center: [-9871995, 3566245],
    zoom: 6,
  }),
  layers: [
    new TileLayer({
      source: new OSM(),
    }),
    new TileLayer({
      opacity: 0.5,
      source: wmtsSource,
    }),
  ],
});

const slider = document.getElementById('slider');
const updateSourceDimension = function () {
  wmtsSource.updateDimensions({'threshold': slider.value});
  document.getElementById('theinfo').innerHTML = slider.value + ' meters';
};
slider.addEventListener('input', updateSourceDimension);
updateSourceDimension();

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>WMTS Tile Transitions</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>
    <label>
      Sea-level
      <input id="slider" type="range" value="10" max="100" min="-1">
    </label>
    <span id="theinfo"></span>

    <script type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "wmts-dimensions",
  "dependencies": {
    "ol": "9.1.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}