Wearable hololgrams. Image tracking with Vuforia and Hololens.

I have been playing around with the new Vuforia support for Hololens and trying to see how well it can track moving objects.  I started with the documentation @ “Developing Vuforia Apps for HoloLens” and my scene is based off the sample scene in the documentation.

The goal is to have a wearable bracelet that can anchor a hologram, using three fiducial markers.

After a number of attempts and tag designs I landed on this design.

The markers can be reliably detected, but a bit big!

The markers can be reliably detected, but a bit big!

My first attempt used tags that were about 1 3/8 inches, and I found it was rarely detecting them, only when really close.

The square target is big enough, the circle is too small to be detected reliably.

The square target is big enough, the circle is too small to be detected reliably.

 

Marker on the left ended up being too small to detect reliably.

Marker on the left ended up being too small to detect reliably.

The tags I ended up using are 2 inches, and can be detected at arms length.

One big gotcha that I have found, when you upload markers to the Vuforia device database, you need to ensure that you enter the correct width, as it is printed in the real world, or holograms will anchor too far above or below the object ( the lens thinks it is closer or further away than it really is )

You also want the “rating” in the Vuforia target manager to be as high as possible, images with lots of features are more augmentable. 1 star rating will not work at all.

There is also a camera setting, Camera Mode (SPEED vs DEFAULT vs QUALITY) results in selecting different camera resolutions, but it is not documented on what exactly is selected. I am using the SPEED setting, which I assume will identify the images quicker? I also have used the QUALITY setting, which did not seem to impact the FPS, speed of detection or distance needed.  Have not found much documentation on it.

Vuforia for Hololens has a feature called “Extended Tracking” that will pin objects to to their last known location when tracking is lost, which is nice if you would like to look away from something and look back and still have it registered.   Given the limited FOV of the camera, it seems you would want to use this feature in all cases where objects are mostly static, but it doesn’t work well for moving objects ( like in this case ) the holograms will get stuck and not update with your movement.

Ultimately, it seems like this sort of image location is really best suited for static objects. It works for a wearable bracelet, but I am thinking technologies like Lighthouse or Zapbox would do much better.

I can't use MRC or take screenshots while vuforia is running, so here is a shot through the lens via cellphone.

I can’t use MRC or take screenshots while Vuforia is running, so here is a shot through the lens via cellphone.

2 Comments

  1. ruth | July 5, 2017 at 6:37 am
     

    Hi Hedley!
    I’m currently trying to implement wearable target markers for AR in the form of stickers for children. I’m using Vuforia for Unity and building to Android. I’m having trouble getting the device to recognise the sticker at all. The sticker is circular and 5cm by 5 cm. Do you have any tips with how to best track wearable AR markers? Have you had any more luck?
    Cheers, ruth

    Reply
    • Hedley Robertson | July 5, 2017 at 8:44 am
       

      Hi Ruth. Do your stickers happen to be glossy or otherwise reflect ambient light? I had terrible results with the stickers I tried to use at first so I ended up printing up markers already designed for machine vision, http://docs.opencv.org/3.1.0/d5/dae/tutorial_aruco_detection.html. This also provides a non-vuforia path, if you wanted to roll your own solution.

      Reply

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