Environments in Roboschool Half-Cheetah



I have some questions regarding the roboschool Half-Cheetah.

  1. I see that the observation space for Half-Cheetah is 26. Can anyone tell me what is each value for - I counted 18? (also, some of the values seem to remain 0 for all timesteps)

  2. In the half_cheetah.xml under roboschool/mujoco_assets, there is the following comment:

Cheetah Model

The state space is populated with joints in the order that they are
defined in this file. The actuators also operate on joints.

State-Space (name/joint/parameter):
    - rootx     slider      position (m)
    - rootz     slider      position (m)
    - rooty     hinge       angle (rad)
    - bthigh    hinge       angle (rad)
    - bshin     hinge       angle (rad)
    - bfoot     hinge       angle (rad)
    - fthigh    hinge       angle (rad)
    - fshin     hinge       angle (rad)
    - ffoot     hinge       angle (rad)
    - rootx     slider      velocity (m/s)
    - rootz     slider      velocity (m/s)
    - rooty     hinge       angular velocity (rad/s)
    - bthigh    hinge       angular velocity (rad/s)
    - bshin     hinge       angular velocity (rad/s)
    - bfoot     hinge       angular velocity (rad/s)
    - fthigh    hinge       angular velocity (rad/s)
    - fshin     hinge       angular velocity (rad/s)
    - ffoot     hinge       angular velocity (rad/s)

Could you please confirm to me if the order presented here is the same with the order they appear in the observation matrix?

Thank you.