Receiving link frame position and orientation in simulation and real robot

[IoannisDadiotis]

@alaurenzi, following the discusion in the previous issue I want to be able to subscribe to position and orientation of the centauro's links.

I suppose /gazebo/link_states topic is not suitable as on the real robot there will be no gazebo running.

Xbotcore publishes the desired data for pelvis and wheel_1 only (to topics/xbotcore/link_state/*). Can xbotcore (or other topic I may have passed by) provide this information for the other frames too?

If this info is not published in a topic yet, I suppose one way is to use /xbotcore/link_state/pelvis and then from TFs (receiving transformation between pelvis and the desired frame) find the position and orientation of the desired frame.

[alaurenzi]

Here the problem is that the pose of the robot base link w.r.t. the world is not measurable. The link_state topics are only available in simulation, and provide the same data as gazebo/link_states. The "real" pose of any of the robot link w.r.t. the world can only be estimated by a suitable base pose estimation algorithm (with @EnricoMingo we are working on one). For any relative pose within the robot, TFs are the way to go.