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Image tracking has a weird offset issue in the Vuforia HoloLens sample containing the MRTK v2.2

May 13, 2020 - 8:20am #1

Hiya!

 

We've been working with the Vuforia Hololens Sample 1 & 2 asset available on the Unity Asset Store for some time now, and while we have been able to get image tracking working in a basic form, we've discovered a strange offset issue that we think is being caused during the initialisation of some part of the Vuforia plugin.

Intermittently, we have encountered what appears to be a random rotational offset in the position of the virtual image target in relation to ise physical print counterpart. Through some experimentation, we discovered that it in fact seems to relate to how much the user changed the orientation & position of their head while the app is loading.

To test this, we set up a basic project and ran a few tests where we would start the app, wait for the 2D unity window to display the Vuforia splash screen, and then turn some significant rotation amount to the left or right from our starting position. Once the app finishes loading we would look at the image target and observe an offset that seemed representative of how much we turned during that app's load.

I've attached a zip to this post that should help to diagnose this issue. It contains a Unity project demonstrating our setup - duplicated directly from the Image Targets sample scene in the framework, along with an AppX demonstrating the issue that is ready for side-loading.

The best way we've found to replicate this bug is to swing your head from side to side as the app loads, to maximise the chance that there will be a random-ish offset once the app has finished loading and the app is ready to track image targets.



Please note that we have seen instances of this issuein HoloLens since as far back as early 2018, when we first started using Vuforia in Hololens apps, so we're aware that is is a long-standing issue. However, we have also used Vuforia in other platforms such as iOS & Android, and we have not encountered this issue on those platforms, so we believe it to be specific to the Vuforia framework(s) for Hololens.



As our client will be deploying these devices to trainees who are not expected to be familiar with the idiosyncrasies of this technology, we need to be able to offer them a solution more robust than the workaround of them telling their trainees to stand still as a statue while the app loads in their headset. So any assistance you can provide to help us fix or bypass this bug would be appreciated!



Thanks!

Image tracking has a weird offset issue in the Vuforia HoloLens sample containing the MRTK v2.2

June 2, 2020 - 5:48am #6

Hi,

Yes, MRTK v2.2 and v2.3; Vuforia: 9.1.7; Unity 2019.2.2.

I've used the HL1+2 sample app for testing.

Thank you.

Vuforia Engine Support

 

Image tracking has a weird offset issue in the Vuforia HoloLens sample containing the MRTK v2.2

May 29, 2020 - 7:55am #5

@mcotora: Could you confirm you were using MRTK v2 instead of HoloToolkit?

If so could you specify which Vuforia library, version of mrtk and unity version you are using?

 

Thanks in advance,

Kind regards,

Mathieu

Image tracking has a weird offset issue in the Vuforia HoloLens sample containing the MRTK v2.2

May 27, 2020 - 11:48pm #4

Hi, 

I've re-tested your scenario with our Hl1+2 sample app. In my tests I have tried different head movements from right to left, creating an arc etc. but was *not* able to reproduce the issue. 

Thank you.

Vuforia Engine Support

Edit: still with a HL2. Will providing findings with HL1 later this week/beginning of next week.

Image tracking has a weird offset issue in the Vuforia HoloLens sample containing the MRTK v2.2

May 17, 2020 - 7:29am #3

mcotora wrote:

Hi,

I tested ImageTargets on a HL2 with Vuforia HL1+2 core sample app

We're using HoloLens 1 as the target platform for this project (a client spec requirement), not HoloLens 2.

mcotora wrote:

Our recommendation would be to redo the calibration and check the display housing for fingerprints which may also degrade the eye tracker accuracy.

This bug is not related to improper calibration. We've seen that issue before as well, it presents quite differently than the issue I described and we know how to fix it when we encounter it.

The issue I described seems to occur somewhere between initialisation of the Unity part of the application, and initialisation/activation of the Vuforia runtime.

It seems that there is some non-zero length of time wherein coordinate systems of the Unity scene hosting the Vuforia behaviour become initialised/active and can change/update before the Vuforia runtime becomes initialised/active. And when this happens, such as when continuously swinging one's head from side to side in wide arcs while the app is loading, one can induce a very large rotational offset of 90 degrees or more.

I have confirmed this in three consecutive instances of the app I compiled using the source project I provided, prior to mking my initial post.

Image tracking has a weird offset issue in the Vuforia HoloLens sample containing the MRTK v2.2

May 15, 2020 - 4:38am #2

Hi,

I tested ImageTargets on a HL2 with Vuforia HL1+2 core sample app and was *partially* able to reproduce a small offset when the IT was recognized, ~1-3mm.

The offset is in the tolerance level of 15% which is impacted by user and camera intrinsic calibration.

Our recommendation would be to redo the calibration and check the display housing for fingerprints which may also degrade the eye tracker accuracy.

Thank you.

Vuforia Engine Support

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