simtk.org

Hallo everybody,

I just started using OpenSim (3.1). I was trying to scale a model, for example gait2354_simbody.osim . To scale the model I use the subject01_Setup_Scale.xml data. Both from the directory Gait2354_Simbody. So far everything works fine.

Now the problem. If I change coordinate tasks in the static pose tab nothing changes in the scaled model. It seems that the coordinate tabs don't effect the result. Otherwise if I change the markertasks (for example the weights) the result is different.

Does anyone know if this is a bug or if I just use the tool wrong.

Thanks for your help.
Nils Kästner

Hi Nils,

"coordinate tasks" are used only if you provide some guess for coordinate values in the form of a coordinates file (e.g. if computed by your motion capture system and you trust that the model used by your motion capture is similar to the model used in OpenSim). If you don't provide coordinates file then I'd expect the coordinate tasks to have no effect whatsoever on the Scaling (or IK).

Please let us know if that explains the behavior.

Best regards,
-Ayman

Hi Nils,

We have replicated this issue in lab. There seems to be a bug which results in the manual coordinates not being included in the IK solution during scaling. This will be addressed in the next release. In the mean time you could try two workarounds...

1) You can prescribe coordinates by using a coordinate file (suggested by Ayman). I havent tested this though so just see how it goes.

2) You can assign (and save) a new set of default coordinates to the model and then 'lock' these coordinates during scaling.

Please let us know how it goes

Cheers,
-James

Hi Ayman, hi James,

if I create a whole coordinate file it effects the result of the scaling tool as it should.

Thanks a lot for your help
Nils Kästner