Hello, I would like to understand the implementation of OpenSim's Inverse kinematics. I have looked at the doxygen page :https://simtk.org/api_docs/opensim/api_docs/classOpenSim_1_1AssemblySolver.html#details and the SimBody theory manual, but I do not completely understand how the optimisation func...

Hi Nicholas, I have two additional questions sorry: 1) When you mention 'dynamically-consistent', what exactly do you mean by that? What are the optimisation variables in MOCO? And if my model had just a pelvis and femur, would the angles between IK and MOCO differ? 2) Is there any influence of scal...

Hi, I have a question regarding IK: If the total residual error or segmental residual error (residual error of markers in a segment) increases, but the joint angle error (compared to reference) decreases, why is the objective function having a greater residual error value? In other words, what can c...

Hello,

I am trying to run IK using trc files found in project (https://simtk.org/projects/models-2-sta). I get this error in the GUI: InverseKinematicsTool Failed: null upcall object in OpenSim::AnalysisWrapper::begin

What does it mean and how to fix it?

Thanks
Vignesh

Hello,

I would like to print the marker residuals after a moco,track problem. I am not able to find the function for this? Any help is hugely appreciated.

Thanks,
Vignesh

Hi Thomas, Sorry I have a follow-up question: 1) Based on my understanding, if I do not have any experimental coordinates, the residual at each frame would just contain the marker residuals. There would not be any influence of calculated unprescribed coordinates in the residual error. Is my understa...

Thanks a lot

Regards,
Vignesh

Hello Thomas,

Thanks a lot. That makes a lot of sense. I shall look into the assemble and track functions. Just to confirm, is there any calculation of angles done in the Kinematics class in InverseKinematicsTool or is it just used for reporting angles?

Regards
Vignesh

Hi Thomas, Thank you. I would like to get some more detail in how the angles are calculated. Once the virtual markers positions are adjusted, how are the joint angles then computed? Are the new positions of the markers used to calculate a new transformation matrix etc? Also, which function in invers...

Hi, @Aaron, not sure if it is too late. From my understanding, if the marker error is 0, it should match the angles calculated using anatomical coordinate frames. That is only if you used a model without constraints. I think adding constraints causes some marker error as some DoF are restricted. Did...