Illustrates how transparency in maps work.

100% © IGN, © iTowns

Transparency in maps (and any other 3D object) is a tricky problem. Due to limitations in how 3D renderers work, it is not generally possible to correctly display overlapping transparent objects. For example, set the opacity of at least 2 maps to less than 100%, rotate the camera around, and observe various rendering issues, such as missing map tiles.

index.js
import colormap from 'colormap';

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

import { Fill, Stroke, Style } from 'ol/style.js';
import TileWMS from 'ol/source/TileWMS.js';
import GeoJSON from 'ol/format/GeoJSON.js';

import BilFormat from '@giro3d/giro3d/formats/BilFormat.js';
import Extent from '@giro3d/giro3d/core/geographic/Extent.js';
import Instance from '@giro3d/giro3d/core/Instance.js';
import TiledImageSource from '@giro3d/giro3d/sources/TiledImageSource.js';
import ColorLayer from '@giro3d/giro3d/core/layer/ColorLayer.js';
import ElevationLayer from '@giro3d/giro3d/core/layer/ElevationLayer.js';
import Map from '@giro3d/giro3d/entities/Map.js';
import Inspector from '@giro3d/giro3d/gui/Inspector.js';
import VectorSource from '@giro3d/giro3d/sources/VectorSource.js';
import ColorMap from '@giro3d/giro3d/core/layer/ColorMap.js';

// # Planar (EPSG:3946) viewer

// Defines projection that we will use (taken from https://epsg.io/3946, Proj4js section)
Instance.registerCRS(
    'EPSG:3946',
    '+proj=lcc +lat_1=45.25 +lat_2=46.75 +lat_0=46 +lon_0=3 +x_0=1700000 +y_0=5200000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs',
);

// Defines geographic extent: CRS, min/max X, min/max Y
const extent = new Extent('EPSG:3946', 1837816.94334, 1847692.32501, 5170036.4587, 5178412.82698);

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

// Creates the Giro3D instance
const instance = new Instance(viewerDiv, {
    crs: 'EPSG:3946',
    renderer: {
        clearColor: false,
    },
});

const terrainMap = new Map('terrain', { extent, doubleSided: true, hillshading: true });
instance.add(terrainMap);

const min = 100;
const max = 300;

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

const elevationLayer = new ElevationLayer({
    name: 'terrain',
    extent,
    colorMap,
    minmax: { min, max },
    source: new TiledImageSource({
        source: new TileWMS({
            url: 'https://data.geopf.fr/wms-r',
            projection: 'EPSG:3946',
            crossOrigin: 'anonymous',
            params: {
                LAYERS: ['ELEVATION.ELEVATIONGRIDCOVERAGE.HIGHRES'],
                FORMAT: 'image/x-bil;bits=32',
            },
        }),
        format: new BilFormat(),
        noDataValue: -1000,
    }),
});

terrainMap.addLayer(elevationLayer);

const orthophotoMap = new Map('orthophoto', { extent, doubleSided: true });
instance.add(orthophotoMap);

const orthophotoLayer = new ColorLayer({
    name: 'orthophoto',
    extent,
    source: new TiledImageSource({
        source: new TileWMS({
            url: 'https://data.geopf.fr/wms-r',
            projection: 'EPSG:3946',
            params: {
                LAYERS: ['HR.ORTHOIMAGERY.ORTHOPHOTOS'],
                FORMAT: 'image/jpeg',
            },
        }),
    }),
});
orthophotoMap.addLayer(orthophotoLayer);

const vectorMap = new Map('geojson', { extent, doubleSided: true, backgroundOpacity: 0 });
instance.add(vectorMap);

const geoJsonLayer = new ColorLayer({
    name: 'geojson',
    extent,
    source: new VectorSource({
        data: 'https://raw.githubusercontent.com/iTowns/iTowns2-sample-data/master/lyon.geojson',
        format: new GeoJSON(),
        dataProjection: 'EPSG:3946',
        style: new Style({
            fill: new Fill({
                color: 'rgba(255, 165, 0, 0.6)',
            }),
            stroke: new Stroke({
                color: 'white',
            }),
        }),
    }),
});

vectorMap.addLayer(geoJsonLayer);

orthophotoMap.object3d.translateZ(+1500);
orthophotoMap.object3d.updateMatrixWorld();
vectorMap.object3d.translateZ(+2500);
vectorMap.object3d.updateMatrixWorld();

// Sets the camera position
instance.camera.camera3D.position.set(1832816, 5163527, 6121);

// Creates controls
const controls = new MapControls(instance.camera.camera3D, instance.domElement);
// Then looks at extent's center
controls.target = extent.centerAsVector3();
controls.saveState();

controls.enableDamping = true;
controls.dampingFactor = 0.2;

instance.useTHREEControls(controls);

Inspector.attach(document.getElementById('panelDiv'), instance);

// Bind events

function bindToggle(id, callback) {
    const toggle = document.getElementById(id);
    toggle.oninput = () => {
        const state = toggle.checked;
        callback(state);
        instance.notifyChange();
    };
}

function bindSlider(id, callback) {
    const slider = document.getElementById(id);
    slider.oninput = function oninput() {
        callback(slider.valueAsNumber);
        instance.notifyChange();
    };
}

bindToggle('show-terrain', v => {
    terrainMap.visible = v;
});
bindToggle('show-orthophoto', v => {
    orthophotoMap.visible = v;
});
bindToggle('show-vector', v => {
    vectorMap.visible = v;
});

bindSlider('terrain-opacity', o => {
    terrainMap.opacity = o;
});
bindSlider('orthophoto-opacity', o => {
    orthophotoMap.opacity = o;
});
bindSlider('vector-opacity', o => {
    vectorMap.opacity = o;
});
bindSlider('vector-bg-opacity', o => {
    vectorMap.materialOptions.backgroundOpacity = o;
    instance.notifyChange(vectorMap);
});
index.html
<!doctype html>
<html lang="en">
    <head>
        <title>Stacking transparent maps</title>
        <meta charset="UTF-8" />
        <meta name="name" content="map_transparency_stack" />
        <meta name="description" content="Illustrates how transparency in maps work." />
        <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="mh-100 overflow-y-auto">
                <!-- Vector map -->
                <div class="card mb-1">
                    <div class="card-header">
                        <div class="form-check form-switch">
                            <input
                                class="form-check-input"
                                checked
                                type="checkbox"
                                role="switch"
                                id="show-vector"
                                autocomplete="off"
                            />
                            <label class="form-check-label" for="show-vector">Vector map</label>
                        </div>
                    </div>

                    <div class="card-body" id="vector-options">
                        <!-- Opacity -->
                        <label for="vector-opacity" class="form-label">Map opacity</label>
                        <div class="input-group">
                            <input
                                type="range"
                                min="0"
                                step="0.01"
                                max="1"
                                value="1"
                                class="form-range"
                                id="vector-opacity"
                                autocomplete="off"
                            />
                        </div>

                        <!-- Opacity -->
                        <label for="vector-bg-opacity" class="form-label">Background opacity</label>
                        <div class="input-group">
                            <input
                                type="range"
                                min="0"
                                step="0.01"
                                max="1"
                                value="0"
                                class="form-range"
                                id="vector-bg-opacity"
                                autocomplete="off"
                            />
                        </div>
                    </div>
                </div>

                <!-- Orthophoto map -->
                <div class="card mb-1">
                    <div class="card-header">
                        <div class="form-check form-switch">
                            <input
                                class="form-check-input"
                                checked
                                type="checkbox"
                                role="switch"
                                id="show-orthophoto"
                                autocomplete="off"
                            />
                            <label class="form-check-label" for="show-orthophoto">Orthophoto map</label>
                        </div>
                    </div>

                    <div class="card-body" id="orthophoto-options">
                        <!-- Opacity -->
                        <label for="orthophoto-opacity" class="form-label">Map opacity</label>
                        <div class="input-group">
                            <input
                                type="range"
                                min="0"
                                step="0.01"
                                max="1"
                                value="1"
                                class="form-range"
                                id="orthophoto-opacity"
                                autocomplete="off"
                            />
                        </div>
                    </div>
                </div>

                <!-- Terrain map -->
                <div class="card mb-1">
                    <div class="card-header">
                        <div class="form-check form-switch">
                            <input
                                class="form-check-input"
                                checked
                                type="checkbox"
                                role="switch"
                                id="show-terrain"
                                autocomplete="off"
                            />
                            <label class="form-check-label" for="show-terrain">Terrain map</label>
                        </div>
                    </div>

                    <div class="card-body" id="terrain-options">
                        <!-- Opacity -->
                        <label for="terrain-opacity" class="form-label">Map opacity</label>
                        <div class="input-group">
                            <input
                                type="range"
                                min="0"
                                step="0.01"
                                max="1"
                                value="1"
                                class="form-range"
                                id="terrain-opacity"
                                autocomplete="off"
                            />
                        </div>
                    </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": "map_transparency_stack",
    "dependencies": {
        "colormap": "^2.3.2",
        "@giro3d/giro3d": "0.37.2"
    },
    "devDependencies": {
        "vite": "^3.2.3"
    },
    "scripts": {
        "start": "vite",
        "build": "vite build"
    }
}