PROWAREtech
ThreeJS: How to Orbit a Body
How to make a 3D/mesh object (the satellite) orbit another object (the body) using THREE.js; how to make a celestial/solar system.
This simple code snippet is all that is needed to make one object (orbiter) orbit another object (body):
// NOTE: speed less than 0 will cause the direction of spin to change; alternatively, multiply the output of cosine by -1
var orbitBody = function (body, orbiter, speed, distanceFromBody) {
var time = Date.now();
orbiter.position.x = Math.cos(time * speed / 1000) * distanceFromBody + body.position.x;
orbiter.position.z = Math.sin(time * speed / 1000) * distanceFromBody + body.position.z;
}
Here is a full working example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Orbiting</title>
<style>
body {
background-color: white;
}
canvas {
display: block;
width: 300px;
height: 300px;
}
</style>
</head>
<body>
<canvas></canvas>
<script src="/js/three.min.js"></script>
<script type="text/javascript">
(function () {
var canvas = document.getElementsByTagName("canvas")[0];
// NOTE: create the scene to place objects in
var scene = new THREE.Scene();
scene.background = new THREE.Color(0x6699CC);
scene.matrixWorldAutoUpdate = true;
// NOTE: the width and height of the canvas
var size = {
width: canvas.offsetWidth,
height: canvas.offsetHeight
};
var cameraNear = 1, cameraFar = 500;
var camera = new THREE.PerspectiveCamera(40, size.width / size.height, cameraNear, cameraFar);
// NOTE: position the camera in space a bit
camera.position.z = 18;
var renderer = new THREE.WebGLRenderer({
canvas: canvas,
antialias: true
});
renderer.setPixelRatio(window.devicePixelRatio);
renderer.setSize(size.width, size.height);
renderer.render(scene, camera);
var light = new THREE.DirectionalLight(0xFFFFFF, 1);
light.position.set(2, 2, 2);
scene.add(light);
scene.add(new THREE.AmbientLight(0xFFFFFF, .2));
var sphereRadius1 = 2;
var sphereGeometry1 = new THREE.SphereGeometry(sphereRadius1, 16, 16);
var sphereRadius2 = 0.5;
var sphereGeometry2 = new THREE.SphereGeometry(sphereRadius2, 16, 16);
var sphereRadius3 = 0.25;
var sphereGeometry3 = new THREE.SphereGeometry(sphereRadius3, 16, 16);
var material = new THREE.MeshLambertMaterial({ color: 0xCC6633 })
var group = new THREE.Group();
var sphere1 = new THREE.Mesh(sphereGeometry1, material);
group.add(sphere1);
var sphere2 = new THREE.Mesh(sphereGeometry2, material);
group.add(sphere2);
var sphere3 = new THREE.Mesh(sphereGeometry3, material);
group.add(sphere3);
scene.add(group);
// NOTE: speed less than 0 will cause the direction of spin to change; alternatively, multiply the output of cosine by -1
var orbitBody = function (body, orbiter, speed, distanceFromBody) {
var time = Date.now();
orbiter.position.x = Math.cos(time * speed / 1000) * distanceFromBody + body.position.x;
orbiter.position.z = Math.sin(time * speed / 1000) * distanceFromBody + body.position.z;
}
var animate = function () {
orbitBody(sphere1, sphere2, 1, 5); // NOTE: better to move sphere2 first
orbitBody(sphere2, sphere3, -3, 1);
renderer.render(scene, camera);
requestAnimationFrame(animate);
};
animate();
})();
</script>
</body>
</html>
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