Frames and Entities

[mxgrey]

As we've discussed, I intend to implement a Frame class that would serve as a base class for things like BodyNodes and EndEffectors. The Frame class would establish a well-defined kinematic tree structure within the DART API that offers new semantics to the user for interacting with data that exists in reference frames.

I was thinking about the concept of an Entity class proposed by JS, and I think it would be a good complement to the Frame class. The Entity class would be a base class for objects that exist within some Frame. It would keep track of what its reference frame is, and it would receive notifications when properties of its reference frame (such as pose, velocity, and acceleration) are changed. The Frame class would inherit the Entity class, since every Frame exists within a reference frame (besides the World Frame, but that's a special case).

I think the Entity class should also encapsulate rendering information, that way the user would be able to easily add renderable objects by creating their own Entities and plugging them into the kinematic tree by giving it a reference frame. Then rendering can be handled by simply traversing the kinematic tree and passing through each Entity.

[mxgrey]

This is now finished in #319