Problems with Scaling and IK

[Paola Castagno]

Hello, I'm a beginner with Opensim, I'm using it for my thesis where I want to compare the kinematic and dynamic results of Vicon system (plug in gait protocol) with the kinematic and dynamic results of Opensim.
I use the gait2354 as model and I have the c3d file from the motion capture trials.
From the c3d files I extracted the file trc of the static trial and the dynamic trial.

Before the scaling I placed the virtual markers on the model (using the GUI interface), following the marker positions of the Plug in Gait.

Then, in the Scaling tool I used the Edit Measurement Set to assign the corresponding pairs of markers to each body.
The resulting scaling seem to be good (I enclose the picture of it below) but in the Messages Window I've seen a big error (in according with the reference of the User Guide):
Frame at (t=0.01): total squared error = 0.0913193, marker error: RMS=0.0644273, max=0.158782 (LTIB)
The max error should be lower, less then 2 cm.

Scaling 2.PNG (29.79 KiB) Viewed 318 times

scaling.PNG (35.91 KiB) Viewed 318 times

don't know how decrease these values, I try to change the Edit Marker Measurement, change the waights, change the virtual markers position but the result doesn't change significantly.

Then, I try to run the Inverse Kinematics and the subject walks badly (I attach the screenshot below) even if the errors are low:

Example: Frame 0 (t=0.01): total squared error = 0.00433898, marker error: RMS=0.015976, max=0.0361602 (LTHI)

IK 2.PNG (23.96 KiB) Viewed 318 times

IK.PNG (35.7 KiB) Viewed 318 times

So, my questions are:
- How can I improve the Scaling?
- The bad result of IK is due to the Scaling?

Thanks for the help.