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Query terrain elevation

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This example uses queryTerrainElevation to display the elevation of a pin which follows a path.

It implements ES6 async functions to increase readability of asynchronous code.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Query terrain elevation</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="https://api.mapbox.com/mapbox-gl-js/v3.8.0/mapbox-gl.css" rel="stylesheet">
<script src="https://api.mapbox.com/mapbox-gl-js/v3.8.0/mapbox-gl.js"></script>
<style>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<script src="https://unpkg.com/@turf/turf@6/turf.min.js"></script>
<div id="map"></div>
<script>
	// TO MAKE THE MAP APPEAR YOU MUST
	// ADD YOUR ACCESS TOKEN FROM
	// https://account.mapbox.com
	mapboxgl.accessToken = 'YOUR_MAPBOX_ACCESS_TOKEN';
    (async () => {
        const map = new mapboxgl.Map({
            container: 'map',
            zoom: 13,
            center: [6.58968, 45.39701],
            pitch: 76,
            bearing: 150,
            // Choose from Mapbox's core styles, or make your own style with Mapbox Studio
            style: 'mapbox://styles/mapbox/satellite-streets-v12',
            interactive: false,
            hash: false
        });

        // Start downloading the route data, and wait for map load to occur in parallel
        const [pinRouteGeojson] = await Promise.all([
            fetch(
                'https://docs.mapbox.com/mapbox-gl-js/assets/route-pin.geojson'
            ).then((response) => response.json()),
            map.once('style.load')
        ]);

        // Set custom fog
        map.setFog({
            'range': [-0.5, 2],
            'color': '#def',
            'high-color': '#def',
            'space-color': '#def'
        });

        // Add terrain source, with slight exaggeration
        map.addSource('mapbox-dem', {
            'type': 'raster-dem',
            'url': 'mapbox://mapbox.terrain-rgb',
            'tileSize': 512,
            'maxzoom': 14
        });
        map.setTerrain({ 'source': 'mapbox-dem', 'exaggeration': 1.5 });

        const pinRoute = pinRouteGeojson.features[0].geometry.coordinates;
        // Create the marker and popup that will display the elevation queries
        const popup = new mapboxgl.Popup({ closeButton: false });
        const marker = new mapboxgl.Marker({
            color: 'red',
            scale: 0.8,
            draggable: false,
            pitchAlignment: 'auto',
            rotationAlignment: 'auto'
        })
            .setLngLat(pinRoute[0])
            .setPopup(popup)
            .addTo(map)
            .togglePopup();

        // Add a line feature and layer. This feature will get updated as we progress the animation
        map.addSource('line', {
            type: 'geojson',
            // Line metrics is required to use the 'line-progress' property
            lineMetrics: true,
            data: pinRouteGeojson
        });
        map.addLayer({
            type: 'line',
            source: 'line',
            id: 'line',
            paint: {
                'line-color': 'rgba(0,0,0,0)',
                'line-width': 5
            },
            layout: {
                'line-cap': 'round',
                'line-join': 'round'
            }
        });

        await map.once('idle');
        // The total animation duration, in milliseconds
        const animationDuration = 20000;
        // Use the https://turfjs.org/ library to calculate line distances and
        // sample the line at a given percentage with the turf.along function.
        const path = turf.lineString(pinRoute);
        // Get the total line distance
        const pathDistance = turf.lineDistance(path);
        let start;
        function frame(time) {
            if (!start) start = time;
            const animationPhase = (time - start) / animationDuration;
            if (animationPhase > 1) {
                return;
            }

            // Get the new latitude and longitude by sampling along the path
            const alongPath = turf.along(path, pathDistance * animationPhase)
                .geometry.coordinates;
            const lngLat = {
                lng: alongPath[0],
                lat: alongPath[1]
            };

            // Sample the terrain elevation. We round to an integer value to
            // prevent showing a lot of digits during the animation
            const elevation = Math.floor(
                // Do not use terrain exaggeration to get actual meter values
                map.queryTerrainElevation(lngLat, { exaggerated: false })
            );

            // Update the popup altitude value and marker location
            popup.setHTML('Altitude: ' + elevation + 'm<br/>');
            marker.setLngLat(lngLat);

            // Reduce the visible length of the line by using a line-gradient to cutoff the line
            // animationPhase is a value between 0 and 1 that reprents the progress of the animation
            map.setPaintProperty('line', 'line-gradient', [
                'step',
                ['line-progress'],
                'red',
                animationPhase,
                'rgba(255, 0, 0, 0)'
            ]);

            // Rotate the camera at a slightly lower speed to give some parallax effect in the background
            const rotation = 150 - animationPhase * 40.0;
            map.setBearing(rotation % 360);

            window.requestAnimationFrame(frame);
        }

        window.requestAnimationFrame(frame);
    })();
</script>

</body>
</html>
This code snippet will not work as expected until you replace YOUR_MAPBOX_ACCESS_TOKEN with an access token from your Mapbox account.
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