[Mujoco] lack of ground truth mode for attitude estimation

[tongtybj]

Mujoco does not support ground truth mode for attitude estimation like Gazebo:
https://github.com/jsk-ros-pkg/jsk_aerial_robot/blob/master/aerial_robot_simulation/src/simulation_attitude_controller.cpp#L63-L77

What is the reason to truncate this function @sugikazu75 ?

[sugikazu75]

I think I could not get baselink velocity and angular velocity using MuJoCo's API. So I gave up to implement grond truth mode for spinal, which requires the true value of angular velocity.

[tongtybj]

@sugikazu75

I see. I also realized it after creating this issue.
A simple workaround is to use the sensor plugin with zero noise to act as a ground truth generator.

• angular velocity: https://mujoco.readthedocs.io/en/stable/XMLreference.html#sensor-gyro
• linear velocity: https://mujoco.readthedocs.io/en/stable/XMLreference.html#sensor-velocimeter

For linear velocity, the value is desribed in local frame. So frame conversion is necessary.