Human motion#

Skeletons#

Skeletons of OptiTrack, Vicon (subjects with several segments) and Qualisys are published on skeletons with the same structure: segments with ids, names, parent and global pose. mocap4r2_marker_viz draws them, and skeleton_publisher turns them into TF (<skeleton>/<segment>, to use RViz or tf2 tools) and joint angles:

$ ros2 run mocap4r2_motion_tools skeleton_publisher --ros-args \
    -r skeletons:=/skeletons

~/joint_states (sensor_msgs/JointState) has three angles per segment with a parent, <skeleton>/<segment>_{x,y,z}: the Cardan XYZ angles (mobile axes) of the segment relative to its parent. Map them to your anatomical convention (e.g. ISB) with the segment axes defined in the mocap software.

Capture sessions#

See Capture sessions to record a trial with every system started at once and its metadata.

Export for biomechanics software#

$ ros2 mocap4r2 export walk01 --format c3d --max-gap 10 --lowpass 6

  • c3d: labeled markers in millimetres, readable by Visual3D, OpenSim, Mokka and ezc3d; missing samples are flagged as invalid.

  • csv: one column per marker coordinate, and one file per rigid body.

  • tum: rigid body trajectories for evo.

--max-gap N fills gaps of up to N frames by linear interpolation; --lowpass F applies a zero-phase second order Butterworth filter (forward and backward, the usual choice for marker data; 6 Hz is common for gait).