Bent over scaled model

[John De Witt]

Hello,
I would call myself an 'intermediate' user of OpenSim as I have spent considerable hours learning the program. I am using OS 2.0.2 to analyze exercise data. I am having a problem that I hope someone can help with.

For each subject, I collected a static trial with a markerset similar to that used in Tutorial 3. When I run the scaling tool, my experimental markers appear in the correct location (as they do when I preview the motion), but my scaled model is flexed at the hips by about 75 degrees. If I increase the pose weights of the head and shoulder markers, the scaled model becomes upright, but essentially by lengthening the femurs. This is not appropriate. Can anyone help here? I would be happy to share the static .trc file I am using.

[Ayman Habib]

Hi John,

Could it be an issue with labeling the markers or the headers of the trc file that cause markers to be mismatched? Can you check the messages window to see what's the marker with max error?

-Ayman

[John De Witt]

I have checked the file to ensure that labelling is correct, and have found no errors, but I will recheck. Is there a way in OS to turn on marker names of a previewed motion?

Here is the message box answer:
Frame 1 (t=0.508): total weighted squared error = 44.3503, marker error: RMS=0.168724, max=0.573811 (Top.Head), coord error: RMS=0.00043458, max=0.000807098 (subtalar_angle_r)

If I look at the model in the output window, the red exeprimental markers appear in space to be where they should be.

The heels of the model after scaling are below the actual locaiton of the heel marker as if the model's legs were forces downward.

[Edith Arnold]

Have you tried running the Scale Tool with "Preview static pose (no marker movement)" checked? I apologize if this is what you meant by "when I preview the motion."

Running scale with this box checked will show you both the virtual markers and the experimental ones, rather than just moving the markers. This is a useful diagnostic trick for scale because you can see if the virtual markers are placed appropriately for your marker convention.

[John De Witt]

I have run the scale tool with the preview static pose and the scaled model is bent over.

I collected my dat awith the BTS Smart-D system, and created custom Matlab code to create the trc file. BTS also allows a direct export of their data into trc files. I have used both methods with the same result, so I am confident my markers are named correctly.

I am thinking that the issue has to do with the model I am using (3DGaitModel2354) and its intial marker positions. However, I thought the scale step is what is used to adjust the marker positions, so I am confused.

[Andrea Morelli]

Hi John,
I also used a BTS SMART-D system and usually i didn't have problem with scaling and I export data directly from BTS tracker.
Did you check that name of the markers in the model is exactly the same of the GaitModel2354 ?
You can check also if axis orientation is correct loading it with "Preview motion data" features in opensim.
If you want I can give a look at it.

Andrea

[John De Witt]

With the help of Andrea Morelli, we were able to correct the problem. I had not changed the scaling factor settings to automatic, and rather had kept them exactly as in the tutorial 3 where manual scales were used for the femur and tibia. Changing the scale factors to automatic corrected the issue. Thanks, Andrea!