How to render an object that always moves along the motion - arcore

Question

I am rendering an object using node.setWorldPosition(0,0,-2f).
But I hope it always shows up in front of my camera view 2 meters away
I tried to display the node that is always facing my camera, but when I move the device forward, I can't move the node. Im not using anchor to fixed my object.
private void nodeAlwaysFaceCamera() {
Vector3 cameraPosition = arFragment.getArSceneView().getScene().getCamera().getWorldPosition();
Vector3 cardPosition = node.getWorldPosition();
Vector3 direction = Vector3.subtract(cameraPosition, cardPosition);
Quaternion lookRotation = Quaternion.lookRotation(direction, Vector3.up());
node.setWorldRotation(lookRotation);
}
Render the object 2 meters in front of the camera
node = new Node();
node.setParent(arFragment.getArSceneView().getScene());
node.setWorldPosition(new Vector3(0f, 0f, -2f));
node.setRenderable(viewRenderable);
My expected result is that the object will stick to the camera while moving.

Answer 1

Instead of getting the world position, you should use the Pose of the Camera. So instead of this
Vector3 cameraPosition = arFragment.getArSceneView().getScene().getCamera().getWorldPosition();
You can use:
Pose cameraPose = arFragment.getArSceneView().getScene().getCamera().getPose();
Or alternatively you can create a new Pose without the rotation of the camera.
Pose cameraPose = arFragment.getArSceneView().getScene().getCamera().getPose().extractTranslation();
Then you can use that pose to compose the pose for the object that you want to have in front of the camera. In example this will place the object in front of the camera at the same height at a distance of 2m (using the second cameraPose):
// Compose the Pose of the Object relative to the cameraPose
Pose objectPose = cameraPose.compose(Pose.makeTranslation(0,0,-2f));
// Create an Anchor for the object
Anchor objectAnchor = arFragment.getArSceneView().getSession().createAnchor(objectPose);
AnchorNode objectAnchorNode = AnchorNode(objectAnchor);
// Here is your code
node = new Node();
node.setParent(anchorNode);
node.setRenderable(viewRenderable);
....