why is projected_gravity calculated from quat_rotate instead of quat_rotate_inverse?

[DeeDive]

Hello authors,

I notice the code here, the base_lin_vel and base_ang_vel is calculated from quat_rotate_inverse; but the projected gravity is from quat_rotate;

base_ang_vel = quat_rotate_inverse(torso_rotation, ang_velocity) * self.ang_vel_scale projected_gravity = quat_rotate(torso_rotation, self.gravity_vec)

https://github.com/NVIDIA-Omniverse/OmniIsaacGymEnvs/blob/4948d18d042ec4f26625b67ce09afaa4b9dcbcc3/omniisaacgymenvs/tasks/anymal.py#L153-L154

While in similar implementations like legged_gym,

self.base_ang_vel[:] = quat_rotate_inverse(self.base_quat, self.root_states[:, 10:13]) self.projected_gravity[:] = quat_rotate_inverse(self.base_quat, self.gravity_vec)

https://github.com/leggedrobotics/legged_gym/blob/20f7f92e89865084b958895d988513108b307e6c/legged_gym/envs/base/legged_robot.py#L120

What do you think?

[SavaltoreHungca]

I have the same question with you, need help.