Scaling and IK Marker Errors in 4.0

[Rachel Baker]

Hello,

I'm using OpenSim 4.0 to reproduce a sit-to-stand transfer in subjects with knee OA. I've previously used both the scaling and inverse kinematics tools in OpenSim 3.1, 3.2, and 3.3 for various simulations, and I've noticed a difference in how the marker errors are calculated/displayed in the Messages window of the OpenSim 4.0 GUI. In the 3.X versions of OpenSim, if a marker was disabled in the Weights tab of either the scaling or IK tool, that marker would not be considered in the either RMS or maximum marker errors, correct? However, in OpenSim 4.0, I've noticed that disabled markers are sometimes reported as the max error (which would make sense if it was not weighted).

Are disabled markers' errors also included in the RMS errors? Is this a known difference between the versions? If so, what is the best practice for dealing with unweighted markers' large errors in scaling and/or IK? For scaling, I just removed markers with large errors from the .trc files as long as they were not lower limb markers or important for scaling the upper extremity. (For example, a wrist marker or a sternum marker on a larger subject.) After scaling a model in this way, I was able to get my IK errors within an acceptable range for my application. I would love some feedback on if I am heading in the right direction or if anyone else has run into this issue as well. If anyone has any advice or a better way of solving these issues, I would really appreciate your input.

Thanks in advance!

Rachel H.

[聂 倩文]

hi, Rachel Baker
i 'd like to conduct a similar simulation about muscle force changing with time during siting to standing.However, i didn't find appropriate experimental data. Would you like to tell me where your data coming from. If you, don't mind, would you like to share it with me? Thank you very much. My email address is 1656853236@qq.com.

Best wishes!
Qianwen Nie

[Isabella Garza]

Hello Rachel,

I am working on a similar application and would love to know if you were able to determine if the disabled marker error was included in the RMS error calculations.

I'm working on a project involving marker weightings and I am trying to find out how OpenSim treats a disabled marker in terms of error calculation. Specifically, I'm trying to understand how OpenSim treats a disabled marker in a marker set with other enabled markers vs. a set of completely disabled markers. When I run inverse kinematics to get the marker trajectory data, only the enabled markers' data are reported. However, when I run inverse kinematics with all markers disabled, all the disabled marker data is reported. I would love any advice or input on this if you were able to figure out the answer to your question.

Thank you!

Isabella G