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Query terrain elevation along a line

This example uses turf.js and queryTerrainElevation to query for elevations at regular intervals between two points. The resulting elevations are displayed in a line chart with chart.js to create a visual elevation profile.

Drag the markers to create a new elevation profile between any two points.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Query terrain elevation along a line</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="https://api.mapbox.com/mapbox-gl-js/v3.2.0/mapbox-gl.css" rel="stylesheet">
<script src="https://api.mapbox.com/mapbox-gl-js/v3.2.0/mapbox-gl.js"></script>
<style>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<style>
#chart-container {
height: 25%;
width: 100%;
position: absolute;
top: 0;
left: 0;
right: 0;
z-index: 10;
background-color: rgba(255, 255, 255, 0.9);
text-align: center;
}

#chart-inner-container {
position: relative;
margin: auto;
height: 100%;
width: 100vw;
}
</style>

<script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
<script src="https://unpkg.com/@turf/turf@6/turf.min.js"></script>
<div id="map">
<div id="chart-container">
<div id="chart-inner-container">
<canvas id="chart-canvas"></canvas>
</div>
</div>
</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', // container ID
style: 'mapbox://styles/mapbox/outdoors-v12', // style URL
bounds: [-71.4, 44.36, -71.08, 44.25279]
});

// default start and end point are defined as a geoJSON LineString
const lineData = {
type: 'Feature',
geometry: {
type: 'LineString',
coordinates: [
[-71.328053, 44.313497],
[-71.12971, 44.25279]
]
},
properties: {}
};

map.on('style.load', () => {
// add source and layer for rendering the line
map.addSource('line-data', {
type: 'geojson',
data: lineData
});

map.addLayer({
id: 'line-line-data',
type: 'line',
source: 'line-data',
paint: {
'line-width': 4,
'line-color': '#37a2eb'
}
});

// add the digital elevation model tiles
map.addSource('mapbox-dem', {
type: 'raster-dem',
url: 'mapbox://mapbox.mapbox-terrain-dem-v1',
tileSize: 512,
maxzoom: 20
});
map.setTerrain({ 'source': 'mapbox-dem', 'exaggeration': 1 });

// add draggable markers
const marker0 = new mapboxgl.Marker({
draggable: true,
color: '#83f7a0'
})
.setLngLat(lineData.geometry.coordinates[0])
.addTo(map);

const marker1 = new mapboxgl.Marker({
draggable: true,
color: '#ed6461'
})
.setLngLat(lineData.geometry.coordinates[1])
.addTo(map);

// as the user drags a marker, update the data for the line and re-render it with setData()
const updateLineData = (e, position) => {
const { lng, lat } = e.target.getLngLat();
lineData.geometry.coordinates[position] = [lng, lat];
map.getSource('line-data').setData(lineData);
};

marker0.on('drag', (e) => {
updateLineData(e, 0);
});
marker0.on('dragend', updateElevationProfile);

marker1.on('drag', (e) => {
updateLineData(e, 1);
});
marker1.on('dragend', updateElevationProfile);
});

const myLineChart = new Chart(document.getElementById('chart-canvas'), {
type: 'line',
data: {
labels: [],
datasets: []
},
options: {
plugins: {
legend: {
display: false
},
title: {
display: true,
align: 'start',
text: 'Elevation (m)'
}
},
maintainAspectRatio: false,
responsive: true,
scales: {
x: {
grid: {
display: false
}
},
y: {
min: 0,
grid: {
display: false
}
}
},
elements: {
point: {
radius: 0
}
},
layout: {
padding: {
top: 6,
right: 20,
bottom: -10,
left: 20
}
}
}
});

function updateElevationProfile() {
// split the line into 1km segments
const chunks = turf.lineChunk(lineData, 1).features;

// get the elevation for the leading coordinate of each segment
const elevations = [
...chunks.map((feature) => {
return map.queryTerrainElevation(
feature.geometry.coordinates[0]
);
}),
// do not forget the last coordinate
map.queryTerrainElevation(
chunks[chunks.length - 1].geometry.coordinates[1]
)
];

// add dummy labels
myLineChart.data.labels = elevations.map(() => '');
myLineChart.data.datasets[0] = {
data: elevations,
fill: false,
tension: 0.4
};
myLineChart.update();
}

// trigger the first chart draw after the DEM tiles have loaded
await map.once('idle');
updateElevationProfile();
})();
</script>

</body>
</html>
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