Display an elevation COG and discard no-data values.

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100% © U.S. Geological Survey

The NoDataOptions of the Layer class can be used to replace no-data values with interpolated neighbouring pixels.

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 CogSource from '@giro3d/giro3d/sources/CogSource.js';
import Instance from '@giro3d/giro3d/core/Instance.js';
import ElevationLayer from '@giro3d/giro3d/core/layer/ElevationLayer';
import ColorLayer from '@giro3d/giro3d/core/layer/ColorLayer.js';
import MaskLayer from '@giro3d/giro3d/core/layer/MaskLayer.js';
import Map from '@giro3d/giro3d/entities/Map.js';
import Inspector from '@giro3d/giro3d/gui/Inspector.js';
import ColorMap, { ColorMapMode } from '@giro3d/giro3d/core/layer/ColorMap.js';

// Define projection that we will use (taken from https://epsg.io/26910, Proj4js section)
Instance.registerCRS(
    'EPSG:26910',
    '+proj=utm +zone=10 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs +type=crs',
);

const extent = new Extent('EPSG:26910', 532622, 569790, 5114416, 5137240);

const center = extent.centerAsVector3();

// `viewerDiv` will contain Giro3D' rendering area (the canvas element)
const viewerDiv = document.getElementById('viewerDiv');

// Instantiate Giro3D
const instance = new Instance(viewerDiv, {
    crs: extent.crs(),
    renderer: {
        clearColor: false,
    },
});

// Instantiate the camera
instance.camera.camera3D.position.set(center.x, center.y - 1, 50000);

// Instantiate the controls
const controls = new MapControls(instance.camera.camera3D, instance.domElement);
controls.enableDamping = true;
controls.dampingFactor = 0.2;
controls.target.set(center.x, center.y, center.z);
instance.useTHREEControls(controls);

// Use an elevation COG with nodata values
const source = new CogSource({
    // https://pubs.er.usgs.gov/publication/ds904
    url: 'https://3d.oslandia.com/dem/msh2009dem.tif',
    crs: extent.crs(),
});

const values = colormap({ colormap: 'viridis', nshades: 256 });
const colors = values.map(v => new Color(v));

const min = 227;
const max = 2538;

const colorMap = new ColorMap(colors, min, max, ColorMapMode.Elevation);

const noDataOptions = {
    alpha: 0,
    maxSearchDistance: 10000,
    replaceNoData: true,
};

const map = new Map('map', {
    extent,
    doubleSided: true,
    backgroundOpacity: 0,
    hillshading: true,
    discardNoData: true,
});

instance.add(map);

let elevationLayer;
let maskLayer;
let colorLayer;

let activeLayer = 0;

function updateActiveLayer() {
    elevationLayer.visible = false;
    maskLayer.visible = false;
    colorLayer.visible = false;

    switch (activeLayer) {
        case 0:
            elevationLayer.visible = true;
            map.materialOptions.backgroundOpacity = 0;
            map.materialOptions.discardNoData = true;
            break;
        case 1:
            maskLayer.visible = true;
            map.materialOptions.backgroundOpacity = 1;
            map.materialOptions.discardNoData = false;
            break;
        case 2:
        default:
            colorLayer.visible = true;
            map.materialOptions.backgroundOpacity = 0;
            map.materialOptions.discardNoData = false;
            break;
    }
}

function buildLayers() {
    map.removeLayer(elevationLayer);
    map.removeLayer(maskLayer);
    map.removeLayer(colorLayer);

    maskLayer = new MaskLayer({
        name: 'mask',
        extent,
        source,
        noDataOptions,
        preloadImages: false,
    });

    elevationLayer = new ElevationLayer({
        name: 'elevation',
        extent,
        source,
        noDataOptions,
        colorMap,
        preloadImages: false,
        minmax: { min, max },
    });

    colorLayer = new ColorLayer({
        name: 'color',
        extent,
        source,
        noDataOptions,
        colorMap,
        preloadImages: false,
    });

    map.addLayer(elevationLayer);
    map.addLayer(maskLayer);
    map.addLayer(colorLayer);

    updateActiveLayer();

    instance.notifyChange(map);
}

// Attach the inspector
Inspector.attach(document.getElementById('panelDiv'), instance);

const alphaReplacementInput = document.getElementById('alphaReplacement');

alphaReplacementInput.addEventListener('change', e => {
    const value = parseInt(e.target.value, 10);
    noDataOptions.alpha = value;
});

const radiusSlider = document.getElementById('maxDistanceSlider');
radiusSlider.oninput = function oninput() {
    noDataOptions.maxSearchDistance = radiusSlider.valueAsNumber;
};

const enableFillNoDataCheckbox = document.getElementById('enableFillNoData');

enableFillNoDataCheckbox.oninput = function oninput() {
    const state = enableFillNoDataCheckbox.checked;
    noDataOptions.replaceNoData = state;
    if (!state) {
        radiusSlider.setAttribute('disabled', !state);
        alphaReplacementInput.setAttribute('disabled', !state);
    } else {
        radiusSlider.removeAttribute('disabled');
        alphaReplacementInput.removeAttribute('disabled');
    }
};

function bindDropdown(id, action) {
    document.getElementById(id).addEventListener('change', e => {
        const value = parseInt(e.target.value, 10);
        action(value);
        instance.notifyChange(map);
    });
}

bindDropdown('noDataLayerSource', v => {
    activeLayer = v;
});

bindDropdown('alphaReplacement', v => {
    noDataOptions.value = v;
});

// Bind events

buildLayers();

document.getElementById('applyChanges').onclick = function onclick() {
    buildLayers();
};
index.html
<!doctype html>
<html lang="en">
    <head>
        <title>No-data elimination</title>
        <meta charset="UTF-8" />
        <meta name="name" content="cog_nodata" />
        <meta name="description" content="Display an elevation COG and discard no-data values." />
        <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/css/example.css"
        />

        <style>
        #viewerDiv canvas {
          background-image: linear-gradient(45deg, #aaaaaa 25%, transparent 25%),
            linear-gradient(-45deg, #aaaaaa 25%, transparent 25%),
            linear-gradient(45deg, transparent 75%, #aaaaaa 75%),
            linear-gradient(-45deg, transparent 75%, #aaaaaa 75%);
          background-size: 20px 20px;
          background-position:
            0 0,
            0 10px,
            10px -10px,
            -10px 0px;
        }
        </style>
    </head>

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

        <div class="side-pane-with-status-bar">
            <div class="card">
                <div class="card-header">Options</div>

                <div class="card-body" id="options">
                    <div class="mb-3">
                        <label for="noDataLayerSource" class="form-label">Layer type</label>
                        <select id="noDataLayerSource" class="form-select" autocomplete="off">
                            <option value="0">Elevation layer</option>
                            <option value="1">Mask layer</option>
                            <option value="2">Color layer</option>
                        </select>
                    </div>

                    <div class="mb-3">
                        <div class="form-check form-switch">
                            <input
                                class="form-check-input"
                                type="checkbox"
                                checked="true"
                                role="switch"
                                id="enableFillNoData"
                                autocomplete="off"
                            />
                            <label class="form-check-label" for="enableFillNoData"
                                >Enable fill no-data</label
                            >
                        </div>
                    </div>

                    <div class="mb-3">
                        <label for="alphaReplacement" class="form-label">Replace no-data pixels with</label>
                        <select id="alphaReplacement" class="form-select" autocomplete="off">
                            <option value="1">Opaque alpha</option>
                            <option value="0" selected>Transparent alpha</option>
                        </select>
                    </div>

                    <div class="mb-3">
                        <label for="maxDistanceSlider" class="form-label">Max distance (meters)</label>
                        <div class="input-group">
                            <input
                                type="range"
                                min="0"
                                max="10000"
                                value="10000"
                                step="100"
                                class="form-range"
                                id="maxDistanceSlider"
                                autocomplete="off"
                            />
                        </div>
                    </div>

                    <div class="mb-3">
                        <button type="button" class="btn btn-primary" id="applyChanges">
                            Apply changes
                        </button>
                    </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_nodata",
    "dependencies": {
        "colormap": "^2.3.2",
        "@giro3d/giro3d": "0.37.2"
    },
    "devDependencies": {
        "vite": "^3.2.3"
    },
    "scripts": {
        "start": "vite",
        "build": "vite build"
    }
}