How can I access the VR headset orientation in Three.js? The WebXRManager doesn't seem to provide a way to do this.
You can extract the orientation from the camera used for rendering the scene. Try the following when presenting:
const position = new THREE.Vector3();
const rotation = new THREE.Quaternion();
const scale = new THREE.Vector3();
// the following line extracts the position, rotation and scale in world space
camera.matrixWorld.decompose( position, rotation, scale );