50.4.1 Additive quaternion filtering
Parents: Quaternion index , which orientation parametrisation to-choose?
Source: Markley 2014
Additive quaternion filtering
Additive quaternion error

Methods of enforcing the normalisation
Renormalise the estimate by brute force

Modify KF update equations to enforce a norm constraint using a Lagrange multiplier
[1] and [2] yield biased estimates of the quaternion
Methods that don’t enforce normalisation
- Define the rotation matrix to be

- guarantees orthogonality
- introduces unobservable DOF: the quaternion norm
- Use the above equation without the ||q||-2 factor –> no orthogonality