Inverse Kinematics Errors

[Jeffrey Min]

Hi everyone,

I am currently on a project using Gait2392 to study knee angles and moments. Something i am trying to wrao my head around is how IK is done and its errors. With scaling, I have managed to get errors under 0.015m but then IK errors end up being 0.40+ m. Is this simply due to soft tissue artefacts and the markers not staying as rigid bodies? If so, what would you recommend trying? I've tried playing around with marker weightings in IK with no success and the only other option I can think of is re-doing scaling. Thanks in advance!

[Thomas Uchida]

You might try adjusting the locations of the markers on the model (marker registration). It is common to iterate between Scaling and IK. There are some tips at the bottom of the Scaling and IK pages in the Confluence documentation:

- Getting Started with Scaling – Best Practices and Troubleshooting: https://simtk-confluence.stanford.edu:8 ... leshooting
- Getting Started with Inverse Kinematics – Best Practices and Troubleshooting: https://simtk-confluence.stanford.edu:8 ... leshooting

The following webinar might be helpful as well: "OpenSim Webinar: Tips and Tricks for Data Collection, Scaling and Inverse Kinematics in OpenSim", on the OpenSimVideos YouTube channel: https://www.youtube.com/watch?v=ZG7wzvQC6eU

[Jeffrey Min]

Thanks for that! I've been through the documentation and watched that video previously, so I'll continue to iterate. I think marker placement could also improve on our end and that should translate into better scaling and IK errors.