Explaining environments in Roboschool Half-Cheetah

Question

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 only 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)


Actuators (name/actuator/parameter):
    - bthigh    hinge       torque (N m)
    - bshin     hinge       torque (N m)
    - bfoot     hinge       torque (N m)
    - fthigh    hinge       torque (N m)
    - fshin     hinge       torque (N m)
    - ffoot     hinge       torque (N m)

Could you please confirm to me if the order presented here is the same with the order they appear in the observation matrix? If so, should I take the values that are always 0 into account?

Thank you.