Getting Started with IMU Inverse Kinematics

The IMU Inverse Kinematics (IK) Tool (available as of OpenSim 4.2) steps through each time frame of experimental data and positions the model in a pose that "best matches" experimental IMU orientations. This "best match" is the pose that minimizes a sum of weighted squared orientation errors.

To launch the IK Tool, select Tools → IMU Inverse Kinematics from the OpenSim main menu bar.

Overview

Inputs and outputs of the IMU IK tool. The file names here are used from the example distributed with the GUI and can be found in Models/Rajagopal_OpenSense.

Inputs

Input files:

1. Model file (e.g., Rajagopal2015_opensense.osim): An OpenSim model with a set of IMUs placed on the model, usually through using the IMU Placer tool.
2. Sensor orientation file in quaternions (e.g., walking_orientations.sto): Experimental orientations, represented with quaternions, for a trial obtained from an IMU system, along with the time range of interest.
3. Settings file (e.g., imuInverseKinematics_Setup.xml): A file containing all the settings information for the IMU IK tool.

Other settings:

1. Data transformation: Space fixed Euler angles (XYZ order) from IMU space to OpenSim
2. Weights: Values for weighting the importance of tracking each IMU's orientation

Outputs

1. Output motion file (e.g., walking_orientations.mot): A motion file containing the generalized coordinate trajectories (joint angles and/or translations) computed by IMU IK.