Vuforia Engine provides information on the pose status for each Observer’s target in a scene. This information helps to maintain an AR experience if changes in the scene occur and provides users with directions (e.g., point the device back at a target or move slower when tracking is lost).
The status type and availability depend on the Observer type. For example, pose and status information are not available for BarcodeBehaviour.
In general, Observations collect a target’s info; its pose (if available), and its status and status info. The status describes each state of the target during the tracking lifecycle. In some tracking failure cases, the Vuforia Engine API provides information on the likely cause of the failure.
The pose status and status info is accessible via the TargetStatus() in the Unity C# API. The supporting status info information is reliant on the pose status of the currently active Observer, e.g., ImageTargetBehaviour.
The pose status will be reported as NO_POSE until the first target is detected.
VuMark, Image, Multi, and Cylinder Targets Status Poses and Status Info
The available pose status and status info provided on Observers of type: Image Target, Cylinder Target, Multi Target, and VuMark are identical. The tracking status can be NORMAL or RELOCALIZING for targets that are tracked and NOT_OBSERVED for targets not being tracked. The following table lists the status relationships:
Status |
Status Info |
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NO_POSE |
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No valid pose available. The target is either not yet detected or tracking of it was lost. |
NOT_OBSERVED |
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Provide the user with visual aid to identify the objects that can be tracked. |
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TRACKED |
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The target is being tracked - indicates normal operation. |
NORMAL |
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Tracking working normally, and augmentations can be rendered. |
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EXTENDED_TRACKED |
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The target is tracked indirectly. It is either out-of-view, occluded, too-far or too-close to be tracked directly but its pose is maintained by the Device Pose Behaviour. Refer to Device Tracking for more details. |
NORMAL |
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Tracking working normally. |
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LIMITED |
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The target is being tracked but only with very low accuracy. If your application requires exact target alignment, it is recommended to discard limited poses of targets. If accurate alignment is less of a concern, then using limited poses may provide a more continuous tracking experience. |
RELOCALIZING |
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Motivate the user to return to the target if needed. |
Model Targets Status Poses and Status Info
The ModelTargetBehaviour inherits the same pose status information but additionally reports about wrongly scaled Model Targets:
Status |
Status Info |
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NO_POSE |
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Vuforia is trying to detect the target but a pose is not available yet. |
NOT_OBSERVED |
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No actions required when this status info is reported. |
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INITIALIZING |
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The target is an Advanced Model Target that has not been recognized yet. We recommend showing a Viewfinder UI if you have multiple targets or a Symbolic Guide View for a single target. |
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RECOMMENDING_GUIDANCE |
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The target does not have an Advanced Guide View. We recommend showing a Guide View Overlay to assist the user in moving to a position where tracking can start. |
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TRACKED |
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The target is being tracked and indicates normal operation. |
NORMAL |
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Circumstances are good, and augmentations can be rendered. |
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WRONG_SCALE |
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Vuforia detects a significant discrepancy between the target and the physical object. The target’s size is either too small or too large up to a factor of 50x compared to the real world size of the tracked object. The target will still track, but reported poses will not be in metrical coordinates. The target will appear at the wrong depth on HoloLens or MagicLeap. It is recommended to correct the scale. |
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EXTENDED_TRACKED |
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The target is tracked indirectly. It is either out-of-view, occluded, too-far or too-close to be tracked directly but its pose is maintained by the Device Pose Behaviour. Refer to Device Tracking for more details. |
NORMAL |
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Motivate the user to return to the target if needed. |
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WRONG_SCALE |
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See TRACKED + WRONG_SCALE. It is recommended to correct the scale. |
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LIMITED |
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The target is being tracked but only with very low accuracy. If your application requires exact target alignment, it is recommended to discard limited poses of targets. If accurate alignment is less of a concern, then using limited poses may provide a more continuous tracking experience. |
RELOCALIZING |
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Motivate user to return to the target if needed. |
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WRONG_SCALE |
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Vuforia detects a huge discrepancy between the target and the physical object. The target’s size is either too small or too large by more than factor of 50x compared to the real word size of the tracked object. Tracking will not work reliably. Make sure to review and correct the scale of the Model Target. |
Area Targets and Anchors Status Poses and Status Info
The following table lists the available pose status values for Area Targets and Anchors:
Status |
Status Info |
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NO_POSE |
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Vuforia is trying to detect the target but a pose is not available yet. |
NOT_OBSERVED |
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Guide the user to a starting position to start or re-enable tracking the environment. |
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EXTENDED_TRACKED |
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The target is being indirectly tracked utilizing the Device Pose Behaviour and is set to operating normally. |
NORMAL |
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Normal target tracking conditions. Augmentations can be rendered with precise alignment. |
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LIMITED |
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The target is being tracked but only with very low accuracy. If your application requires exact target alignment, it is recommended to discard LIMITED poses of targets. If accurate alignment is less of a concern, then using LIMITED poses may provide a more continuous tracking experience. |
RELOCALIZING |
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A limited pose of a target is known to have substantially larger inaccuracies than a normal extended tracked pose. Once the inferred pose of the target or anchor is estimated more accurately, it will again start to report extended tracked poses. |
NOTE: AreaTargetBehaviour and AnchorBehaviour are always reported as NORMAL for extended tracked poses and RELOCALIZING for limited poses.
You can choose which statuses should be active in the Unity Editor by selecting a target’s DefaultObserverEventHandler component. See Using the Device Tracking in Unity for more information.
Device Tracking Status Poses and Status Info
The Device Pose Behaviour represents a special case in tracking since it does not track the pose of an object in front of the camera, but rather the pose of the device with respect to the surrounding environment.
Device tracking uses Vuforia Fusion to utilize the core technologies available for each individual platform. The pose status and status information affected by the individual platforms is abstracted and consolidated by Vuforia Engine. See the table below for details.
The VuDevicePoseBehaviour is used to track the device’s 6-degrees-of-freedom poses in the environment (e.g., when used in combination with Ground Plane or Area Targets)
Status |
Status Info |
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NO_POSE |
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No device pose available. |
NOT_OBSERVED |
UNKNOWN |
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Vuforia cannot determine a device pose or provide information on the reason. |
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Reset the Device Pose Behaviour with Reset() or instruct the user to restart the entire AR experience when the situation is continuously reported for a certain length of time (e.g., 10 seconds). |
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INITIALIZING |
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The device tracking is initializing. |
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Instruct the user to wait and to move the device slightly around. Vuforia reports this status using any provider to allow a consistent app behavior. On ARKit this is reported when no pose is delivered just after starting a ARSession. |
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RELOCALIZING |
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The device is trying to re-attach to the world and restore Anchor locations. |
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Instruct the user to go back to a previously seen area. Reset the device pose or instruct the user to restart the entire AR experience when the situation is continuously reported for a certain length of time (e.g., 10 seconds). Some Anchors might not be reported after a relocalization. We recommend cleaning these up sometime after relocalization occurs. This status info is not reported on ARKit. In this status info, when using VISION_ONLY and detecting a previously undetected target, the device pose status switches to LIMITED/INITIALIZING after a short delay. This indicates that no relocalization occurred but internally the device pose was re-started. Previous mid-air anchors are lost. Other anchors and targets might be re-detected. |
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LIMITED |
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The device pose is of degraded quality. The application may advise the user to help recover a better device tracking. Anchor creation is not recommended. There are no guarantees about the accuracy or consistency of new anchors and creation may fail if there is not sufficient scene geometry. |
UNKNOWN |
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Vuforia is not capable of providing information on the cause of the limited pose. |
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Advise the user to hold the device still and check that lighting conditions are suitable and that the tracked area has sufficient visual features. A degraded 3-degree-of-freedom pose might be available as a fall back. |
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INITIALIZING |
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The device tracking is initializing. |
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Instruct the user to move the device around to achieve better quality tracking. |
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RELOCALIZING Only reported on ARKit |
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The device is trying to re-attach to the world and restore Anchor locations. |
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Instruct the user to return to a previously seen area. If the situation is reported for a certain length of time (e.g., 10 seconds), reset the device pose or instruct the user to restart the entire AR experience. Some Anchors/targets might not be reported after a relocalization. We recommend cleaning these up sometime after relocalization occurs. NOTE: The length of time depends on the expected user behavior and your use case. |
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EXCESSIVE_MOTION Only reported on ARKit |
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The device is being moved too fast. |
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Instruct the user to move slower or hold the device still. |
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INSUFFICIENT_FEATURES Only reported on ARKit |
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The device is pointed at an area with very few visual features. While sensor readings support device tracking, the visual odometry system also relies on visual features in the environment. |
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Instruct the user to point to an area with more visual features or check for proper lighting and contrast. |
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INSUFFICIENT_LIGHT Only reported on ARCore |
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Motion tracking is lost due to poor lighting conditions. |
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Instruct the user to move to a more brightly lit area. |
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TRACKED |
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A reliable device pose is provided, and experiences are anchored with respect to the environment. |
NORMAL |
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Normal device tracking conditions. |
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Time to render your full augmented experience. NOTE: Hit test may still fail in certain cases (e.g., if insufficient scene geometry was discovered by the underlying platform or when pointing in a direction with no surface to hit). |
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Handling of Status and Status Info in Unity
Most ObserverBehaviour in Unity, including Image Targets, Model Targets, Area Targets and Anchors, come with the DefaultObserverEventHandler that handles Status updates out of the box.
By default, this event handler will show and hide augmentations parented to the target game object based on the current Status. A dropdown in the inspector lets you configure which Status values should be considered for showing the augmentation.
For more complex use cases, you can directly subscribe to the OnTargetStatusUpdated event of an ObserverBehaviour. This event is available for all Observer Behaviours, including the DevicePoseBehaviour and will be invoked whenever the OnStatusChanged is triggered.
The following example shows a setup for subscribing and processing this event:
using UnityEngine;
using Vuforia;
public class StatusEventHandler : MonoBehaviour
{
private ObserverBehaviour mObserverBehaviour;
void Awake()
{
ObserverBehaviour mObserverBehaviour = GetComponent<ObserverBehaviour>();
if (mObserverBehaviour != null)
mObserverBehaviour.OnTargetStatusChanged += OnStatusChanged;
}
void OnStatusChanged(ObserverBehaviour behaviour, TargetStatus status)
{
Debug.LogFormat("TargetName: {0}, Status is: {1}, StatusInfo is: {2}", behaviour.TargetName, status.Status, status.StatusInfo);
}
void OnDestroy()
{
if (mObserverBehaviour != null)
mObserverBehaviour.OnTargetStatusChanged -= OnStatusChanged;
}
}