Scaling model results in separating body.

[Quinten Humphrey]

Hello all,

I scaled a model but it resulted in separating the body in half at the lumbar spine.

Screenshot (80).png (318.57 KiB) Viewed 388 times

I have been trying to figure out how to fix this issue but seem to be stuck. I imagine it might have something to do with the IVD joint between L3 and L4, but am not sure if that is the case. If you have any suggestions, I would appreciate it. Thank you.

[Ayman Habib]

Hi Quintin,

It is important to understand how scaling works and how it affects different components of an OpenSim model when using the scale tool. If bodies are attached using joints then the locations where the joint frames are attached to their corresponding bodies are scaled based on computed scale factors. This works relatively intuitively out of the box, especially if the scale factors are close which is typical. However, in a case where some "constraint" is used to relate bodies rather than a joint, this mechanism may not work if the constraint can't be generically scaled by the code. Assuming this is your case then you'll need to manually modify the constraint post scaling to put the model together again.

Please let us know what you find out.

Best regards,
-Ayman

[Quinten Humphrey]

Thank you for your help. What I have done so far is change the location of the L3 IVD joint so it aligns with the lower extremities. I then ran the IK tool and what happened was the upper body, starting from the L3 IVD joint location going up, translated down towards the sacrum.

[Quinten Humphrey]

I believe I figured it out. It involved editing the translations in the spatial transform of the L3_L4_IVDjoint