Animate a point along a route | TrackAsia GL JS Docs

Use Turf to smoothly animate a point along the distance of a line.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Animate a point along a route</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-gl.js"></script>
<link href="https://unpkg.com/trackasia-gl@1.0.5/dist/trackasia-gl.css" rel="stylesheet" />
<style>
	body { margin: 0; padding: 0; }
	#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<style>
.overlay {
position: absolute;
top: 10px;
left: 10px;
}
 
.overlay button {
font: 600 12px/20px 'Helvetica Neue', Arial, Helvetica, sans-serif;
background-color: #3386c0;
color: #fff;
display: inline-block;
margin: 0;
padding: 10px 20px;
border: none;
cursor: pointer;
border-radius: 3px;
}
 
.overlay button:hover {
background-color: #4ea0da;
}
</style>
<script
src="https://www.unpkg.com/turf@2.0.0/turf.min.js"
charset="utf-8"
></script>
 
<div id="map"></div>
<div class="overlay">
<button id="replay">Replay</button>
</div>
 
<script>
var map = new trackasiagl.Map({
container: 'map',
style: 'https://maps.track-asia.com/styles/v1/streets.json?key=public_key',
center: [107.645112,16.376013],
zoom: 4
});
 
var origin = [106.660172,10.762622];
 
// Intermediate point
var point_one = [108.898371,11.988816];
var point_two = [107.645112,16.376013];
var point_three = [104.962697,19.252034];
 
var destination = [105.800481,21.220949];
 
// A simple line from origin to destination.
var route = {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'LineString',
'coordinates': [origin, point_one, point_two, point_three, destination]
}
}
]
};
 
// A single point that animates along the route.
// Coordinates are initially set to origin.
var point = {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'properties': {},
'geometry': {
'type': 'Point',
'coordinates': origin
}
}
]
};
 
// Calculate the distance in kilometers between route start/end point.
var lineDistance = turf.lineDistance(route.features[0], 'kilometers');
 
var arc = [];
 
// Number of steps to use in the arc and animation, more steps means
// a smoother arc and animation, but too many steps will result in a
// low frame rate
var steps = 500;
 
// Draw an arc between the `origin` & `destination` of the two points
for (var i = 0; i < lineDistance; i += lineDistance / steps) {
var segment = turf.along(route.features[0], i, 'kilometers');
arc.push(segment.geometry.coordinates);
}
 
// Update the route with calculated arc coordinates
route.features[0].geometry.coordinates = arc;
 
// Used to increment the value of the point measurement against the route.
var counter = 0;
 
map.on('load', function () {
// Add a source and layer displaying a point which will be animated in a circle.
map.addSource('route', {
'type': 'geojson',
'data': route
});
 
map.addSource('point', {
'type': 'geojson',
'data': point
});
 
map.addLayer({
'id': 'route',
'source': 'route',
'type': 'line',
'paint': {
'line-width': 2,
'line-color': '#007cbf'
}
});
 
map.addLayer({
'id': 'point',
'source': 'point',
'type': 'symbol',
'layout': {
'icon-image': 'airport',
'icon-rotate': ['get', 'bearing'],
'icon-rotation-alignment': 'map',
'icon-overlap': 'always',
'icon-ignore-placement': true
}
});
 
function animate() {
// Update point geometry to a new position based on counter denoting
// the index to access the arc.
point.features[0].geometry.coordinates =
route.features[0].geometry.coordinates[counter];
 
// Calculate the bearing to ensure the icon is rotated to match the route arc
// The bearing is calculate between the current point and the next point, except
// at the end of the arc use the previous point and the current point
point.features[0].properties.bearing = turf.bearing(
turf.point(
route.features[0].geometry.coordinates[
counter >= steps ? counter - 1 : counter
]
),
turf.point(
route.features[0].geometry.coordinates[
counter >= steps ? counter : counter + 1
]
)
);
 
// Update the source with this new data.
map.getSource('point').setData(point);
 
// Request the next frame of animation so long the end has not been reached.
if (counter < steps) {
requestAnimationFrame(animate);
}
 
counter = counter + 1;
}
 
document
.getElementById('replay')
.addEventListener('click', function () {
// Set the coordinates of the original point back to origin
point.features[0].geometry.coordinates = origin;
 
// Update the source layer
map.getSource('point').setData(point);
 
// Reset the counter
counter = 0;
 
// Restart the animation.
animate(counter);
});
 
// Start the animation.
animate(counter);
});
</script>
 
</body>
</html>