"XrCreateSpatialAnchorsAsync in the Magic Leap API failed. Reason: PoseInvalid"

Unity Development
,
1

The main object in our app gets an anchor after two seconds of not being manipulated. For most objects this goes without a problem. Some objects completely disappear after getting an anchor.

After logging some stuff, I found the following. First, I exactly print out the lossy scale, word position and world rotation, and I get:

Ensuring anchor for (Transform) Patient3D Hologram ; lossyScale: (1.00, 1.00, 1.00), world pos: (-0.29, 0.78, 0.62), world rot: (0.00000, 1.00000, 0.00000, 0.00000)

Directly after that I add the anchor. Basically, “gameObject.AddComponent<ARAnchor>”

Like I said, for most objects this goes without a hitch. However, some objects completely disappear, and then I see in the log the following three errors:

Msg: Error: XrCreateSpatialAnchorsAsync in the Magic Leap API failed. Reason: PoseInvalid
StackTrace: UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
MagicLeap.OpenXR.Utils:DidXrCallSucceed(XrResult, String, Predicate`1, Boolean)
MagicLeap.OpenXR.Subsystems.MagicLeapProvider:TryAddAnchor(Pose, XRAnchor&)
UnityEngine.GameObject:AddComponent()

Msg: XRAnchorSubsystem: Error creating Anchor at ((-0.29, 0.78, 0.62), (0.00000, 1.00000, 0.00000, 0.00000))
StackTrace: UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
MagicLeap.OpenXR.Subsystems.MagicLeapProvider:TryAddAnchor(Pose, XRAnchor&)
UnityEngine.GameObject:AddComponent()

XRAnchorSubsystem: Failed Deleting Anchor from Subsystem 0000000000000000-0000000000000000
StackTrace: UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
MagicLeap.OpenXR.Subsystems.MagicLeapProvider:TryRemoveAnchor(TrackableId)
UnityEngine.GameObject:AddComponent()

For the sake of being thorough, my OpenXR settings:

image
image653×864 26 KB

What the hell is wrong with this seemingly perfectly valid pose? Also, this happens always with some objects. It is perfectly reproducible. Other objects never fail. So it is not a tracking issue. For some reasons, one object always fails, some objects never. I have to add it is a large-ish compound object. However, with no anchor attached ML2 has no issue displaying it at all.

Edit: I also printed out the world matrix of the offending object:

— — — —
-1.00000 0.00000 0.00000 -0.06836
0.00000 1.00000 0.00000 0.77463
0.00000 0.00000 -1.00000 0.48522
0.00000 0.00000 0.00000 1.00000

I also did print that from object that has no issues:

— — — —
-0.99175 0.07537 0.10372 -0.09752
0.07038 0.99622 -0.05101 0.04878
-0.10717 -0.04329 -0.99330 0.22585
0.00000 0.00000 0.00000 1.00000

Using:

  • Unity 6000.49.f1
  • ML2 OS 1.12.0
  • Magic Leap SDK 2.6.0
  • Magic Leap MRTK 1.4.0
  • Host OS: Windows.
1 Like
2

To answer my own question - apparently your anchoring system has issues with ‘perfect rotations’. After a long debugging session, and some help from Gemini 2.5 pro, this is the solution. Just prior to adding an anchor, run this code:

public static void SanitizeTransformForAnchor(this Transform targetTransform)
{
    // 1. Check for negative scale via the matrix determinant. A negative value indicates a reflection.
    if (targetTransform.localToWorldMatrix.determinant < 0)
    {
        Debug.LogError($"Anchor pose rejected: Transform '{targetTransform.name}' or one of its parents has a negative scale (a reflection), which is not supported. Please correct the scale in the hierarchy.");
        return;
    }

    // 2. Check for "perfect" or "singular" rotations that might be unstable.
    // We detect this by checking if the rotation matrix has an unusually high number of zero elements.
    var m = targetTransform.localToWorldMatrix;
    var nearZeroElements = 0;
    for (var i = 0; i < 3; i++)
    {
        for (var j = 0; j < 3; j++)
        {
            // Check if the absolute value of the element in the 3x3 rotation part is very close to zero.
            if (Mathf.Abs(m[i, j]) < 1e-5f)
            {
                nearZeroElements++;
            }
        }
    }
    
    // A general rotation has few zero elements. A perfect axis-aligned rotation has 6 or more.
    // If we detect such a matrix, we apply a tiny perturbation to nudge it into a more stable state.
    if (nearZeroElements >= 6)
    {
        Debug.LogWarning($"Potential unstable matrix detected for '{targetTransform.name}'. Applying a small rotational perturbation to ensure stability.");
        targetTransform.rotation *= Quaternion.Euler(0.001f, 0.001f, 0.001f);
    }
}

Now this is quite a dirty hack, I suggest you fix that in your code :wink:

3

Joost, did you try inverting the 1 to -1. This would be the same rotation I think (check please) because a quaternion can be inverted to get the same result. Maybe the ML only can work with one of the two. So it would be (0, -1, 0, 0)