ARTrackedImageManager, when is target "removed"

My assumption is about the three lists are

The first frame a target is detected, it's in "added". And other frames the same target is in "updated". Nothing is ever "removed" in my testing, so I don't know when something is "removed".


https://docs.unity3d.com/Packages/c...on_ARTrackedImageManager_trackedImagesChanged

 

Anyone?

 

This is entirely up to the Provider (e.g. ARCore/ARKit).
Thus, Images could potentially be removed when they are out of frame, when they are obstructed, or not at all.

Edit: Furthermore:
"And other frames the same target is in "updated"."
This is only if the image is actually 'updated' (e.g. if the Provider updates the Pose of the Image).
This behaviour should not be depended upon. Use Added to find it, and check whether its pose is in (proper) view of the camera yourself. If the Pose is updated, check the new Pose. If the camera-pose changes, check that against the latest received Pose of the Image.