erratic world origin/alignment for ARSessionConfiguration.WorldAlignment = .gravityAndHeading

Question

[Note: this question was written against the beta version of ARKit during the iOS11/High Sierra prerelease period. Preserved for historical interest only]

I'm seeing erratic placement and orientation for the world origin when I set the ARWorldTrackingSessionConfiguration.worldAlignment to .gravityAndHeading.

The position of the origin is steady after the scene opens. But the axes are often rotated 180 degrees or 90 degrees around the Y axis.

Is there an additional setting I'm missing? I'm running a 2017 iPad (vanilla, not Pro) and Xcode 9 beta 2. I've tested a few compass apps on this iPad and they give me correct results, so I believe the hardware is working correctly.

override func viewDidLoad() {
    super.viewDidLoad()
    
    // Set the view's delegate
    sceneView.delegate = self
    
    // Show statistics such as fps and timing information
    sceneView.showsStatistics = true
    
    // Create a new scene
    let scene = SCNScene()

    // debug options
    let debugOptions: SCNDebugOptions = [ARSCNDebugOptions.showFeaturePoints,ARSCNDebugOptions.showWorldOrigin]
    sceneView.debugOptions = debugOptions

    // Set the scene to the view
    sceneView.scene = scene
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    
    // Create a session configuration
    let configuration = ARWorldTrackingSessionConfiguration()
    configuration.worldAlignment = .gravityAndHeading
    configuration.planeDetection = .horizontal

    // Run the view's session
    sceneView.session.run(configuration)
}

Here are some samples (in all of them I'm facing south).

Positive X and Z point west and north (incorrect, 180 degrees out of phase):

Positive X and Z point east southeast and south southwest (close to correct):

Positive X and Z point east and south (correct), but origin is displaced a couple of meters:

Positive X and Z point south and west (90 degrees out of phase):

From the .gravityAndHeading documentation:

The y-axis matches the direction of gravity as detected by the device's motion sensing hardware; that is, the vector (0,-1,0) points downward.

The x- and z-axes match the longitude and latitude directions as measured by Location Services. The vector (0,0,-1) points to true north and the vector (-1,0,0) points west. (That is, the positive x-, y-, and z-axes point east, up, and south, respectively.)

Answer 1

I realize this is an old thread, however even with ARKit 2 release and I am using iOS 12, Xcode 10.1 with iPhone 8, I am still getting inconsistent world origin. In some cases where the blue line should be pointing to South, it is actually pointing to East or West.

I did try Sander's suggestion by using the location manager heading, but it is still not 100% guarantee I am getting the right direction to begin with.

Anyone has any other suggestion?