If this is the current state of the art, are there generally-available/open-source libraries existing that implement this and practitioners use for this?
The only one I could find is https://github.com/kartikmohta/manifold_cdkf, which currently has 8 Github stars.
I also found an approach mentioned in [2] that is to just treat a single rotation angle as linear, and then wrap it around at 180 degrees in between state updates with additional conditional logic. Is this what people did in practice before? I cannot find substantial info on this.
How did people use KF on physical objects before 2010?
[2]: https://old.reddit.com/r/ControlTheory/comments/d2yrjq/kalma...
> All People I have interacted with have never seen Kalman Filters outside Academica. Do anyone here have industry experience where Kalman Filters is actually used in prod?
Looking at prior academic work in an academic paper won't help answer this question.
The authors of [1] do discuss and link to their own library in section 5.
However, in my experience, most people implement the math themselves rather than use any libraries (beyond e.g. Eigen).
> How did people use KF on physical objects before 2010?
The Multiplicative EKF (MEKF) was used since 1969 according to [3]. It's a hacky approximation of [1]. [1] is really just a generalization/unification of lots of application-specific hacks that were used before, including the MEKF.
[3]: https://ntrs.nasa.gov/api/citations/20040037784/downloads/20...
The naive Kalman filter is only suited for linear problems; extended and unscented Kalman filters (EKF/UKF) are necessary for anything non-linear (including rotation). In any case, they build on the basic KF, so you have to understand that first.