In which frames is the IMU data expressed?

[stephane-caron]

The IMU field in the observation dictionary contains data like so:

{
  "linear_acceleration": [
    0.0079445635178187,
    4.439796721811672e-06,
    0.00017145108524911683
  ],
  "angular_velocity": [
    1.1916298054173672e-05,
    -0.018927168979633598,
    1.3641552245686093e-05
  ],
  "orientation": [
    -1.1888706467289014e-05,
    0.0048754503950476655,
    2.35814877669327e-06,
    0.9999881386756897
  ]
}

What are the units and in which frames are these quantities expressed?

[stephane-caron]

These three fields are documented on the observations page and in the ImuData class. Both angular velocity and (proper) linear acceleration are expressed in the IMU frame.