Incorrect pelvis coordinates when loading model into OpenSim 4

[Benjamin F]

Hi,

As we all know, most models limit the ROM of the pelvis to 90 and -90 degrees respectively. In OpenSim you can, therefore, increase the ROM by (1) modifying the pelvis_rotation in the model xml file or (2) modifying the ROM directly in the GUI trough coordinateset.

However, in OpenSim 4 it simply seems to disregard any modification to the pelvis_rotation in the xml file and thus induces problems for subjects turning around more than 90 degrees. I can load a model in OpenSim 3.3 that works perfectly on >90 degree trials that won't work in OpenSim 4.

Is there another way to solve this problem in OpenSim 4?

Also, after scaling the model there is quite an offset between the experimental and model markers on the upper extremity of the model (see image). Is there any step you would suggest doing before running simulations?

Thank you,
Ben

[jimmy d]

in OpenSim 4 it simply seems to disregard any modification to the pelvis_rotation in the xml file

I am not seeing that behavior. If I make a copy of the gait2392 model and edit the .osim file, changing the pelvis_rotation range from plus/minus 1.57079633 to plus/minus 3.14, I see that the model can now rotate plus/minus 180 degrees in the GUI.

How are you making the edits? Are you sure you are opening the edited model in the GUI?

[jimmy d]

Your original model is an older version and OpenSim 4.0 is trying to do some updates to the model and getting the conversion wrong. The issue here is that OpenSim 4.0 allows you to open the model at all, it should return an error and tell you to update the model using an intermediate OpenSim version. This is why you can load the model in OpenSim 3.3, save it, and load it successfully in OpenSim 4.0; the 3.3 version does the required model updates.

So, if you want to use this model in 4.0, you will have to use 3.3 to update the model, permanently.