Elevation GeoTIFF

Display an elevation GeoTIFF with a color map.

Read COG as

A GeoTIFF that contains elevation data in 32-bit floating point values. You can visualize the dataset in the following ways: as an elevation layer with or without a color map, as a color layer compressed to 8-bit using Interpretation.CompressTo8Bit, and as a color layer with a ColorMap.

index.js

import colormap from "colormap";

import { Color } from "three";
import { MapControls } from "three/examples/jsm/controls/MapControls.js";

import Extent from "@giro3d/giro3d/core/geographic/Extent.js";
import GeoTIFFSource from "@giro3d/giro3d/sources/GeoTIFFSource.js";
import Instance from "@giro3d/giro3d/core/Instance.js";
import ColorLayer from "@giro3d/giro3d/core/layer/ColorLayer.js";
import ElevationLayer from "@giro3d/giro3d/core/layer/ElevationLayer.js";
import Interpretation from "@giro3d/giro3d/core/layer/Interpretation.js";
import Map from "@giro3d/giro3d/entities/Map.js";
import Inspector from "@giro3d/giro3d/gui/Inspector.js";
import ColorMap, { ColorMapMode } from "@giro3d/giro3d/core/ColorMap.js";

function makeColorRamp(
  preset,
  discrete = false,
  invert = false,
  mirror = false,
) {
  let nshades = discrete ? 10 : 256;

  const values = colormap({ colormap: preset, nshades });

  const colors = values.map((v) => new Color(v));

  if (invert) {
    colors.reverse();
  }

  if (mirror) {
    const mirrored = [...colors, ...colors.reverse()];
    return mirrored;
  }

  return colors;
}

function bindDropDown(id, onChange) {
  const element = document.getElementById(id);
  if (!(element instanceof HTMLSelectElement)) {
    throw new Error(
      "invalid binding element: expected HTMLSelectElement, got: " +
        element.constructor.name,
    );
  }

  element.onchange = () => {
    onChange(element.value);
  };

  const callback = (v) => {
    element.value = v;
    onChange(element.value);
  };

  const setOptions = (options) => {
    const items = options.map(
      (opt) =>
        `<option value=${opt.id} ${opt.selected ? "selected" : ""}>${opt.name}</option>`,
    );
    element.innerHTML = items.join("\n");
  };

  return [callback, element.value, element, setOptions];
}

const extent = new Extent(
  "EPSG:3857",
  -13581040.085,
  -13469591.026,
  5780261.83,
  5942165.048,
);

const instance = new Instance({
  target: "view",
  crs: extent.crs,
});

instance.view.camera.position.set(-13656319, 5735451, 88934);

const controls = new MapControls(instance.view.camera, instance.domElement);
controls.enableDamping = true;
controls.dampingFactor = 0.2;
controls.target.set(-13545408, 5837154, 0);
instance.view.setControls(controls);

const map = new Map({
  extent,
  backgroundColor: "gray",
  lighting: true,
});
instance.add(map);

// Use an elevation COG with nodata values
const source = new GeoTIFFSource({
  // https://www.sciencebase.gov/catalog/item/632a9a9ad34e71c6d67b95a3
  url: "https://3d.oslandia.com/cog_data/COG_EPSG3857_USGS_13_n47w122_20220919.tif",
  crs: extent.crs,
});

const min = 263;
const max = 4347;

// Display it as elevation and color
const viridis = new ColorMap({
  colors: makeColorRamp("viridis"),
  min,
  max,
  mode: ColorMapMode.Elevation,
});
const magma = new ColorMap({
  colors: makeColorRamp("magma"),
  min,
  max,
  mode: ColorMapMode.Elevation,
});

// Attach the inspector
Inspector.attach("inspector", instance);

function updateMode(value) {
  map.removeLayer(map.getLayers()[0]);

  switch (value) {
    case "elevation-colormap":
      map.addLayer(
        new ElevationLayer({
          name: value,
          extent,
          source,
          colorMap: viridis,
          minmax: { min, max },
        }),
      );
      break;
    case "elevation":
      map.addLayer(
        new ElevationLayer({
          name: value,
          extent,
          source,
          minmax: { min, max },
        }),
      );
      break;
    case "8bit":
      map.addLayer(
        new ColorLayer({
          name: value,
          extent,
          source,
          interpretation: Interpretation.CompressTo8Bit(min, max),
        }),
      );
      break;
    case "colormap":
      map.addLayer(
        new ColorLayer({
          name: value,
          extent,
          source,
          colorMap: magma,
        }),
      );
      break;
    default:
      break;
  }

  instance.notifyChange(map);
}

bindDropDown("mode", updateMode);

updateMode("elevation");

index.html

<!doctype html>
<html lang="en">
  <head>
    <title>Elevation GeoTIFF</title>
    <meta charset="UTF-8" />
    <meta name="name" content="cog_elevation" />
    <meta
      name="description"
      content="Display an elevation GeoTIFF with a color map."
    />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />

    <link rel="icon" href="https://giro3d.org/images/favicon.svg" />
    <link
      href="https://giro3d.org/assets/bootstrap-custom.css"
      rel="stylesheet"
    />
    <script src="https://giro3d.org/assets/bootstrap.bundle.min.js"></script>
    <link
      rel="stylesheet"
      type="text/css"
      href="https://giro3d.org/latest/examples/css/example.css"
    />
  </head>

  <body>
    <div id="view" class="m-0 p-0 w-100 h-100"></div>
    <div
      id="inspector"
      class="position-absolute top-0 start-0 mh-100 overflow-auto"
    ></div>

    <div class="side-pane-with-status-bar">
      <!-- Top color layer -->
      <div class="card">
        <div class="card-body">
          <div class="input-group">
            <span class="input-group-text flex-grow-1">Read COG as</span>
            <select
              class="btn btn-outline-primary btn-sm"
              id="mode"
              autocomplete="off"
            >
              <option selected value="elevation">Elevation layer</option>
              <option value="elevation-colormap">
                Elevation layer (with colormap)
              </option>
              <option value="8bit">Color layer (compressed to 8-bit)</option>
              <option value="colormap">Color layer (with colormap)</option>
            </select>
          </div>
        </div>
      </div>
    </div>

    <script type="module" src="index.js"></script>
    <script>
      /* activate popovers */
      const popoverTriggerList = [].slice.call(
        document.querySelectorAll('[data-bs-toggle="popover"]'),
      );
      popoverTriggerList.map(
        // bootstrap is used as script in the template, disable warning about undef
        // eslint-disable-next-line no-undef
        (popoverTriggerEl) =>
          new bootstrap.Popover(popoverTriggerEl, {
            trigger: "hover",
            placement: "left",
            content: document.getElementById(
              popoverTriggerEl.getAttribute("data-bs-content"),
            ).innerHTML,
            html: true,
          }),
      );
    </script>
  </body>
</html>

package.json

{
    "name": "cog_elevation",
    "dependencies": {
        "colormap": "^2.3.2",
        "@giro3d/giro3d": "0.42.4"
    },
    "devDependencies": {
        "vite": "^3.2.3"
    },
    "scripts": {
        "start": "vite",
        "build": "vite build"
    }
}