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1.9.5
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upkie 6.1.0
Open-source wheeled biped robots
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Data from the onboard inertial measurement unit (IMU). More...
#include <ImuData.h>
Public Attributes | |
| Eigen::Quaterniond | orientation_imu_in_ars = Eigen::Quaterniond::Identity() |
| Rotation from the IMU frame to the ARS frame. More... | |
| Eigen::Vector3d | angular_velocity_imu_in_imu = Eigen::Vector3d::Zero() |
| Body angular velocity of the IMU frame in [rad] / [s]. More... | |
| Eigen::Vector3d | linear_acceleration_imu_in_imu = Eigen::Vector3d::Zero() |
| Linear acceleration of the IMU, with gravity filtered out, in [m] / [s]². More... | |
| Eigen::Vector3d | raw_angular_velocity = Eigen::Vector3d::Zero() |
| Raw angular velocity read by the IMU, in [rad] / [s]. More... | |
| Eigen::Vector3d | raw_linear_acceleration = Eigen::Vector3d::Zero() |
| Proper linear acceleration read by the IMU, in [m] / [s]². More... | |
| Eigen::Vector3d | linear_velocity_imu_in_world = Eigen::Vector3d::Zero() |
| Spatial linear velocity in [m] / [s]. More... | |
Data from the onboard inertial measurement unit (IMU).
| Eigen::Vector3d upkie::cpp::actuation::ImuData::angular_velocity_imu_in_imu = Eigen::Vector3d::Zero() |
Body angular velocity of the IMU frame in [rad] / [s].
The full name of the body angular vector would be "angular velocity IMU to world in IMU", but as for all body angular velocities, "angular velocity Body to X in Body" is the same for all inertial frames X (that have zero velocity relative to the world frame). See for instance https://scaron.info/robotics/screw-theory.html#body-screws for the math.
| Eigen::Vector3d upkie::cpp::actuation::ImuData::linear_acceleration_imu_in_imu = Eigen::Vector3d::Zero() |
Linear acceleration of the IMU, with gravity filtered out, in [m] / [s]².
This quantity corresponds to SPI register 34 from the pi3hat https://github.com/mjbots/pi3hat/blob/master/docs/reference.md#imu-register-mapping from which gravity has been substracted out https://github.com/mjbots/pi3hat/blob/4a3158c831da125fa9c96d64378515c1fdb2083f/fw/attitude_reference.h#L147.
| Eigen::Vector3d upkie::cpp::actuation::ImuData::linear_velocity_imu_in_world = Eigen::Vector3d::Zero() |
Spatial linear velocity in [m] / [s].
This field is not an IMU measurement. It is used for instance in the Bullet spine to compute IMU accelerations by finite differences.
| Eigen::Quaterniond upkie::cpp::actuation::ImuData::orientation_imu_in_ars = Eigen::Quaterniond::Identity() |
Rotation from the IMU frame to the ARS frame.
The attitude reference system frame has +x forward, +y right and +z down, whereas our world frame has +x forward, +y left and +z up: https://github.com/mjbots/pi3hat/blob/ab632c82bd501b9fcb6f8200df0551989292b7a1/docs/reference.md#orientation
| Eigen::Vector3d upkie::cpp::actuation::ImuData::raw_angular_velocity = Eigen::Vector3d::Zero() |
Raw angular velocity read by the IMU, in [rad] / [s].
This raw angular velocity measurement may differ from the filtered one (although as of writing this the UKF angular-velocity bias is always zero).
| Eigen::Vector3d upkie::cpp::actuation::ImuData::raw_linear_acceleration = Eigen::Vector3d::Zero() |
Proper linear acceleration read by the IMU, in [m] / [s]².
The acceleration read by an accelerometer is:
\[ {}_I a_{WI} - {}_I g \]
with \({}_I a_{WI}\) the proper linear acceleration of the IMU frame \(I\), and \({}_I g\) the standard acceleration of gravity in the IMU frame. Pay attention to the fact that
Pay attention to the fact that proper acceleration is different from coordinate acceleration, which would be the acceleration of the IMU with respect to the mobile IMU frame in this case. (There is a gyroscopic term in the latter but not in the former.) See for instance the Wikipedia Accelerometer article.
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