Scaling and Inverse Kinematics dont work- Model constraints

[Monica Armengol]

Hello,

I am using model Gait2392. I have load my static data.

If I try to scale without any constraints (as you do in the examples & tutorials), it twists the skeleton completely. I can only manage to keep the skeleton in the write position by locking a lot of the joints in "Coordinates" tab.

If I do this and then try to apply IK, it makes the skeleton twist again.


My questions are:
(1) Based on examples, it seems that scale should be relatively straight forward. I've checked my markers and they look ok. I've even tried superimposing the experimental markers with the skeleton as much as I can and still the results are not optimal. Why do you think this happens?. Any tips to improve this part?

(2) Is locking coordinates the right way to get a model to scale?. If yes, how many constraints is reasonable before forcing the movement to do what you want.

Thanks in advance for your help,

Best wishes,

Monica

[Bryce Killen]

Hi Monica,

Depending on how you are running the scaling tool, it actually contains two tools, a scaling process but also a marker placer.

I usually take the approach of first running the scaling tool without the marker placer then running with marker place without the scaling tool. His could potentially isolate your issue.

When you run the marker placer tool you change the coordinates of the model to match the motion capture markers to some degree . Something that comes to mind when you mention 'twisting' to check is that if you "preview experimental data" and look at your markers to make sure they are where you expect them to be. By this I mean that they are in the same global reference system as opensim meaning the x,y,z convention.

Hopefully this gives you some ideas on what to check.

Cheers
Bryce