Three.js - Rotating a sphere around a certain axis

15
votes

I have a problem. In Three.js, I want to rotate a sphere (Earth) around axis tilted by 23.5 degs. I found sphere.rotation.x, sphere.rotation.y and sphere.rotation.z, but when I combine them in the correct ratio, the sphere's rotation is quite weird - it has no permanent rotation axis. I think I need a function like sphere.rotation.vector(1,0,-1). Does anyone know how this function is called and how the correct syntax is?

Many thanks for answers!

4
javascriptvectorrotationthree.jsaxis

4 Answers

20
votes

You need to use quaternions for this. This video explains what quaternions are and how they are used in 3D graphics.

You can construct a quaternion like this:

quaternion = new THREE.Quaternion().setFromAxisAngle( axisOfRotation, angleOfRotation );

Then you apply it to your object by:

object.rotation.setEulerFromQuaternion( quaternion );

You can also achieve this by using object hierarchies. For example, you can make an Object3D() instance and tilt it by 23.5 degs, then create a sphere (Earth) and add it to the tilted object. The sphere will then rotate around the tilted Y axis. Quaternions however, are the best tool for solving this.

30
votes

You do not have to understand how Euler angles or quaternions work to do what you want. You can use

Object3D.rotateOnAxis( axis, angle );
Object3D.rotateOnWorldAxis( axis, angle );

Make sure axis is a unit vector (has length 1), and angle is in radians.

Object3D.rotateOnAxis( axis, angle ) rotates on an axis in object space.

Object3D.rotateOnWorldAxis( axis, angle ) rotates on an axis in world space.

three.js r.104

2
votes
var quaternion = new THREE.Quaternion();
var object = scene.getObjectByName('xxx');
function render(){
    quaternion.setFromAxisAngle(new THREE.Vector3(0, 1, 0).normalize(), 0.005);
    object.position.applyQuaternion(quaternion);
}

three.js version is 86, see full example on codepen.

0
votes

You can rotate your sphere using th 'ObjectControls' module for ThreeJS that allows you to rotate a single OBJECT (or a Group), and not the SCENE.

Include the libary:

then

var controls = new THREE.ObjectControls(camera, renderer.domElement, yourMesh);

You can find here a live demo here: https://albertopiras.github.io/threeJS-object-controls/

Here is the repo: https://github.com/albertopiras/threeJS-object-controls.

Hope this helps