Find an alternative way to get angular velocity

[tckarenchiang]

Since the getAngularVelocity() in farmsim is very likely calculated wrt the world frame, we need to find another way to compute the local angular velocity.

There is a module in python to estimate the angular velocity given quaternion array and the corresponding time array at which quaternion is measured.

Not yet tested but it could be a good start.

[gavanderhoorn]

Could we perhaps transform the velocity back to a vehicle-local frame?