Subject distorted after Scaling

[Stefanie Gassel]

Hello there,

whenever I try to compute the scaling for the ulb fullbody model in OpenSIM 3.3 (scale file attached), the model gets distorted. E.g. the thorax is displaced in y-Direction and the joints and bodies get sheared and stretched (view image attached). I try to scale only the right arm, leaving the rest of the body as is with manual scaling set to 1.0, which had worked fine with the Hamner model. The Message window doesn't give any warnings or abnormalities apart from "Updating Model file from 20200 to latest format...". The model's total mass is indicated to be 40kg because many body parts don't have mass and inertia values. Could that cause the problem?

I thought the problem lies in my model markers, however the result is very similar when I do the scaling with default values (without any markers, just manual scaling of 1.0 for every body part. (view image 2: test - all body parts set to 1.0, only upper and lower arm set to 1.3)

I was also trying to scale the MoBL UL upper limb model (by Saul et al., 2014) in OpenSIM 3.1 on a different Computer, which has a similar setup for the upper arm, yet is much simplified and has inertia and mass values. The result is similar too. The thorax vanishes and the elbow joint e.g. gets totally distorted, by just running the scale tool with default parameters and manual scale to 1.0.

When trying to scale the Hamner Model with default parameters it works as expected, staying just as it is.

Do you have any ideas, where this could be caused from? What happens, when you try to scale with default parameters (just deselecting the option Adjust Model Markers)?
But if scaling doesn't work for the ULB-model, how could I fit the size of the subject I recorded the motion for to the model? Inverse Kinematics seems to work, however the size doesn't fit.

Thank you! Any help is appreciated!
Stefanie

[Stefanie Gassel]

And here is the output in the messages window, when performing the scale step with the above indicated scale setup file

[Stefanie Gassel]

And here is another image to demonstrate the problem:
Original ulb model (left) and scaled to defaults (1.3 for right arm and 1.0 for the rest of the body) (right)

Thank you very much for your help!
Stefanie

[Patrick Fasbender]

Dear Stefanie,

I encountered the same problem for the Full Body model. The reason for that is, that the full body model uses different reference frames for some of the segments. If you have a look at the Author box in the Model Properties, it provides you with these information.

In order to solve this problem, you have to change the GeometryPath used by Opensim for this model. In order to do that, go to Edit->Preferences. Then change the GeometryPath to the Geometry folder downloaded with the Full Body model.

This helped me solve that problem for the Full Body model.

Kind regards
Patrick Fasbender

[Stefanie Gassel]

Hallo Patrick,
thank you very much for your help and sorry for the late reply! Referencing the geometry folder coming with the ULB model - which the MoBL Upper Limb Model that I'm using is derrived from - solved the visibility problem.

Thank you!
Stefanie

[Hari S]

Thank you. It was helpful for me too.

Your skeleton looks cool with the long neck.