NDVI from a Sentinel 2 COG

Calculating NDVI and applying a custom color map.

The GeoTIFF layer in this example draws from two Sentinel 2 sources: a red band and a near infrared band. The layer style includes a color expression that calculates the Normalized Difference Vegetation Index (NDVI) from values in the two bands. The interpolate expression is used to map NDVI values to colors.

main.js

import 'ol/ol.css';
import GeoTIFF from 'ol/source/GeoTIFF';
import Map from 'ol/Map';
import TileLayer from 'ol/layer/WebGLTile';

const source = new GeoTIFF({
  sources: [
    {
      // visible red, band 1 in the style expression above
      url: 'https://sentinel-cogs.s3.us-west-2.amazonaws.com/sentinel-s2-l2a-cogs/2020/S2A_36QWD_20200701_0_L2A/B04.tif',
      max: 10000,
    },
    {
      // near infrared, band 2 in the style expression above
      url: 'https://sentinel-cogs.s3.us-west-2.amazonaws.com/sentinel-s2-l2a-cogs/2020/S2A_36QWD_20200701_0_L2A/B08.tif',
      max: 10000,
    },
  ],
});

const map = new Map({
  target: 'map',
  layers: [
    new TileLayer({
      style: {
        color: [
          'interpolate',
          ['linear'],
          // calculate NDVI, bands come from the sources below
          [
            '/',
            ['-', ['band', 2], ['band', 1]],
            ['+', ['band', 2], ['band', 1]],
          ],
          // color ramp for NDVI values, ranging from -1 to 1
          -0.2,
          [191, 191, 191],
          -0.1,
          [219, 219, 219],
          0,
          [255, 255, 224],
          0.025,
          [255, 250, 204],
          0.05,
          [237, 232, 181],
          0.075,
          [222, 217, 156],
          0.1,
          [204, 199, 130],
          0.125,
          [189, 184, 107],
          0.15,
          [176, 194, 97],
          0.175,
          [163, 204, 89],
          0.2,
          [145, 191, 82],
          0.25,
          [128, 179, 71],
          0.3,
          [112, 163, 64],
          0.35,
          [97, 150, 54],
          0.4,
          [79, 138, 46],
          0.45,
          [64, 125, 36],
          0.5,
          [48, 110, 28],
          0.55,
          [33, 97, 18],
          0.6,
          [15, 84, 10],
          0.65,
          [0, 69, 0],
        ],
      },
      source: source,
    }),
  ],
  view: source.getView(),
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>NDVI from a Sentinel 2 COG</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-math",
  "dependencies": {
    "ol": "6.12.0"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}