Precision Issues During Calibration - Overabsorbing Aruco Markers

While using a new set of four A3 calibration markers set up to hopefully speed up calibration of our 10-camera, 2.4m diameter rig, we encountered a couple of issues with finding it near-impossible to get any kind of precision from our calibration, resulting in marvelous messes like this sort of thing:

Which, while entertaining, is not super helpful for any kind of filming.

We tried everything we could to try and improve the calibration, including asking Depthkit support directly for help. They directed us to try reducing the Sheer Angle…

Adjusting the Depth Bias in Unity…
At the default of 0.8 it looks like above on the marker box, and this on a human:

At 0.0:

And at 1.5:

…before we finally double-checked the markers in the Azure Kinect Viewer and discovered the source of our current nightmare: The markers we printed are Just Too Good at absorbing IR light and it’s creating gaping holes in the depth data while calibrating.

The holes are shown on the depth data on the top right, compared next to the 100% working calibration board supplied with Depthkit, and a 100% not working ordinary-laser-printed-onto-A4-paper we did as a test.

This is really not a problem we ever would have considered as possible, so massive thanks to the Depthkit team for pointing us towards it.

As our local printing options are obviously a tad limited and we’d like to get a good calibration done as soon as possible, we’ve gotten a bit creative to fix the problem, and experimented with different craft papers to find one that absorbed just the right amount of IR light. Thankfully we lucked out, and managed to find 150g/m² black art paper that seems to do the trick until we can find better printing options. After carefully cutting out a lot of little squares, we’ve now got a new calibration box that seems to be working a lot better!

So, if you’re having calibration issues, don’t feel like waiting for a custom print job, and are okay with fiddling around with millimeter-precise paper-cutting, a trip to the local craft store might just be worth your time :joy:

@Ky_HGL Amazing work here - both in diagnosing, and crafting custom markers! I am glad you were able to get to the bottom of this one. I will update our documentation on ArUco printing with these findings.

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