
Show HN: Chordata – The motion capture system that you can build yourself - daylankifky
https://chordata.cc/
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detaro
Cool project, cheap mocap is a quite an interesting field.

I would have expected a system based purely on such sensors would start to
drift and accumulate errors over time. Are there any tricks used to compensate
for that?

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daylankifky
Thanks! It is not a trick, it's what's called a _Sensor fusion algorithm_.
They come in many flavors, we currently implement Madgwick's one. Another
popular and somehow more robust alternatives are Kalman filters, we'll
probably also implement one of those in the future.

They all rely on absolute references (gravity and magnetic field) to build a
non-drifting reference frame which is used to correct the integration of
(angular) accelerations.

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detaro
Right, totally spaced on that you'd of course get a gravity vector from the
sensors too.

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diveanon
The facial mocap system we used for the short thanos scene in the first
avengers was an Xbox Kinect and some open source libraries.

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daylankifky
So you were on the production of the first avengers movie?

Something like the kinect can be very powerful for facial tracking. But
monocular optical techniques tend to give poor body capture results.

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diveanon
Yes.

The tracking data was not used for the final rendering, but was a basis for
the animation team to work from.

You can definitely see how much it has improved when comparing that scene to
the more recent iterations thanos.

