Restructure Space

[nstarman]

It's currently too flexible. We should make a structure that requires a Position, and optionally has Velocity, Acceleration, etc.

[adrn]

Agreed ^. Also I keep thinking about the name. I really want it to be something like: ExtendedPhaseSpacePosition (too verbose). I stumbled on these discussions that make me think KinematicState or something in that direction might be relevant.