ARKit: How to reset world orientation after interruption

Question

I'm trying to get the ARWorldTracking session to re-orient north after a session interruption. I've went over the documentation a few times but I'm finding it confusing.

Current Behavior:

When I lock the device and reopen the app, triggering the sessionWasInterrupted, the SCNNodes all shift counterclockwise on the compass by ~90 degrees or so.

When you call the run(_:options:) method with a configuration of a different type than the session's current configuration, the session always resets tracking

I interpreted that as saying that when I generate a new set of configurations that is different from the viewWillAppear, the session will "reset". I'm not getting what is actually happening, but the orientation after interruption is off. (and removeExistingAnchors does nothing)

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    let configuration = ARWorldTrackingSessionConfiguration()
    configuration.planeDetection = .horizontal
    configuration.worldAlignment = .gravityAndHeading   
    sceneView.session.run(configuration)
}

func sessionWasInterrupted(_ session: ARSession) {
    let configuration = ARWorldTrackingSessionConfiguration()
    configuration.planeDetection = .horizontal
    configuration.worldAlignment = .gravityAndHeading
    self.sceneView.session.run(configuration, options: [ARSession.RunOptions.removeExistingAnchors, ARSession.RunOptions.resetTracking])
}

Desired Behavior:

When the app detects a session interruption, I'd like it to re-orient itself back to true north.

Answer 1

This issue was killing me, too - you helped me out with half the solution - adding the 'Reset tracking / Remove existing anchors' flags was the magic key for me - I think the other half is the guidance from This post where you have to pause your session and remove all the nodes from the scene, then re-position them. The combination of both of these things got the compass to reset back to True North after session interruption for me.

func resetARSession() {
    // Called by sessionInterruptionDidEnd

    sceneView.session.pause()
    sceneView.scene.rootNode.enumerateChildNodes { (node, stop) in
        node.removeFromParentNode() }
    setupARSession()
    setupSceneView()
}

func setupARSession() {

    let configuration = ARWorldTrackingConfiguration()
    configuration.worldAlignment = .gravityAndHeading
    sceneView.session.run(configuration, options: [ARSession.RunOptions.resetTracking, ARSession.RunOptions.removeExistingAnchors])

}