Hello,

Hope you are doing well. I have a question. I am using a dataset where I have a scaled model and I would like to know if I change the joints of the scaled model (editing the osim file), would it invalidate the scaling?

Thanks

Hello, I have a question regarding using joint centres using scaling. I understand that you scale segment lengths using calculated joint centres but do you need to adjust the osim model joint centre location also? Or does it always remain constant in the segment reference frame? For example, if I ca...

Sorry, adding to that question:

Were the guidelines for marker residual error stated in the inverse kinematic page, determined from literature? If not, how was the 2cm rms error decided upon?

Thanks

Thank you. So in your opinion, can we infer the accuracy of the kinematics from residual error (either global or total)? For example, I get an increase in residual error despite the joint error reducing (during swing) and vice versa in stance. Is there no correlation or relationship between residual...

Hi Thomas, Thanks for your reply. But if the inverse kinematics equations adjusts angles such that the marker residuals are reduced, wouldnt it imply that there should be a direct relationship between marker residuals and joint angle errors (increase in residual error implying an increase in joint a...

Hello, I am investigating the affect of STA on joint kinematics using Lamberto's data (https://simtk.org/projects/models-2-sta/). I find that the joint angle error (difference between calculated joint angle for one subject with reference joint angle) is higher during stance phase and reduces during ...

Hi, Any luck with this? I have got results where the residual error decreases but the joint angle error increases. Can you tell me what may cause this? Does an increase in residual error affect the calculated velocities or accelerations more? The model has been scaled and all model markers placed co...

Hello Nicos, Thanks. I shall look them up. I have one additional question: 1) Does the algorithm ensure that the calculated leg segment remains constant at all frames? For example, if translations are not allowed, to ensure that segment length remains constant, would be greater residual and joint an...

Hello Nicholas, Thank you for your answers. Just to give some background, I am trying to analyse if the marker residual error is a good metric to determine how well the subsequent analyses would be. And for that, I would like to understand the least squares optimisation and what constraints are to b...

Hi Nicholas, Thanks a lot for your reply. Sorry, I have one additional question. I understand that the algorithm used between OpenSim IK and Moco differ, I would like to know, how the optimisation function works in detail. Specifically, 1) What is the optimisation function for marker tracking or tra...