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Band Selection and Contrast Stretch

geozarr3 zarr3 style26

Choosing bands and applying contrast stretch

This example shows how to load multiple bands from a GeoZarr and use the layer.updateStyleVariables() method to update the rendering based on user selected bands and contrast stretch parameters.

main.js
import Map from 'ol/Map.js';
import {getView, withExtentCenter, withHigherResolutions} from 'ol/View.js';
import TileLayer from 'ol/layer/WebGLTile.js';
import GeoZarr from 'ol/source/GeoZarr.js';
import OSM from 'ol/source/OSM.js';

const channels = ['red', 'green', 'blue'];
for (const channel of channels) {
  const selector = document.getElementById(channel);
  selector.addEventListener('change', update);

  const input = document.getElementById(`${channel}Max`);
  input.addEventListener('input', update);
}

function getVariables() {
  const variables = {};
  for (const channel of channels) {
    const selector = document.getElementById(channel);
    variables[channel] = parseFloat(selector.value);

    const inputId = `${channel}Max`;
    const input = document.getElementById(inputId);
    variables[inputId] = parseFloat(input.value);
  }
  return variables;
}

const source = new GeoZarr({
  url: 'https://s3.explorer.eopf.copernicus.eu/esa-zarr-sentinel-explorer-fra/tests-output/sentinel-2-l2a-staging/S2B_MSIL2A_20251115T091139_N0511_R050_T35SLU_20251115T111807.zarr',
  group: 'measurements/reflectance',
  bands: ['b04', 'b03', 'b02', 'b11'],
});

const layer = new TileLayer({
  style: {
    variables: getVariables(),
    gamma: 1.5,
    color: [
      'array',
      ['/', ['band', ['var', 'red']], ['var', 'redMax']],
      ['/', ['band', ['var', 'green']], ['var', 'greenMax']],
      ['/', ['band', ['var', 'blue']], ['var', 'blueMax']],
      [
        'case',
        [
          '==',
          [
            '+',
            ['band', ['var', 'red']],
            ['band', ['var', 'green']],
            ['band', ['var', 'blue']],
          ],
          0,
        ],
        0,
        1,
      ],
    ],
  },
  source,
});

function update() {
  layer.updateStyleVariables(getVariables());
}

const map = new Map({
  target: 'map',
  layers: [new TileLayer({source: new OSM()}), layer],
  view: getView(source, withHigherResolutions(2), withExtentCenter()),
});
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Band Selection and Contrast Stretch</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      .controls {
        display: grid;
        grid-template-columns: auto auto 1fr;
        align-items: baseline;
        gap: 0 1em;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div class="controls">
      <label for="red">Red channel</label>
      <select id="red">
        <option value="1" selected>visible red</option>
        <option value="2">visible green</option>
        <option value="3">visible blue</option>
        <option value="4">short-wave infrared</option>
      </select>
      <label>max
        <input type="range" id="redMax" value="0.3" min="0.2" max="0.5" step="0.01">
      </label>

      <label for="green">Green channel</label>
      <select id="green">
        <option value="1">visible red</option>
        <option value="2" selected>visible green</option>
        <option value="3">visible blue</option>
        <option value="4">short-wave infrared</option>
      </select>
      <label>max
        <input type="range" id="greenMax" value="0.3" min="0.2" max="0.5" step="0.01">
      </label>

      <label for="blue">Blue channel</label>
      <select id="blue">
        <option value="1">visible red</option>
        <option value="2">visible green</option>
        <option value="3" selected>visible blue</option>
        <option value="4">short-wave infrared</option>
      </select>
      <label>max
        <input type="range" id="blueMax" value="0.3" min="0.2" max="0.5" step="0.01">
      </label>
    </div>

    <script type="module" src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "geozarr-stretch",
  "dependencies": {
    "ol": "10.7.1-dev"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}