simtk.org

Hi

I'm trying to do "Tutorial 3 - Scaling, Inverse Kinematics, and Inverse Dynamics"
during scaling process I'm do the following:
1. run scale tool while "preview static pose checkbox" is check .
2. load associated data "static pose .trc"
3. compare the virtual marker, ie. pink ones, to experimental markers, ie. blue ones.
4. adjust pink markers with blue ones.
5. save the new marker set to a .xml file.
6. run scale tool with the new marker set. (I don't close the scale tool from the last time I opened it)

but the marker errors do not reduce to less than this:
Frame at (t=0): total squared error = 0.0266989, marker error: RMS=0.0261646, max=0.0545411 (L.Knee.Med)

even after I un-check the "preview static pose checkbox" the markers exactly match each other, but still this error exists.

what am I missing?

Regards,
Sara.

Hi Sara,

You should overlay the scaled model with static trial data to see how they compare, you're not supposed to manually adjust/move markers by hand.

I don't believe step 5 is part of the tutorial, even though such functionality is available in the application.
If the instructions are not clear, we'd appreciate if you point us to the steps you followed so that we can clarify the documentation/tutorial as needed. Keep in mind that you 're working with version 3.3 and some instructions may have changed for 4.0+ so make sure to use the right version of the tutorial for your environment.

Best regards,
-Ayman

Thanks Ayman for your quick reply.

I'm trying to follow the "Evaluating your results Video Tutorial"
in the link below:
https://www.youtube.com/watch?v=7STRMJefzpI

Also scale tool documentation, under the "Previewing Scale Solution and Static Pose
", states that:
Frequently, it is helpful to preview the inverse kinematic solution for the static pose before adjusting the positions of the model markers. This can be useful for identifying markers that are poorly placed on the model that you may need to manually adjust or may decide not to include in the inverse kinematic problem.

by step 3 and 4 I mean overlaying the scaled model with static trial data to see how they compare.
Because we don't have photos and videos of the subject during static trial, as mentioned in the video, to compare virtual markers to the photos in order to correct their position, I load associated data, subject01_static.trc, for gait2354 to compare and correct marker positions and reduce scaling error in the next run of the scale tool.

I do step 5 because in the video tutorial, the tutor closes the model with inaccurate marker set, opens a model with a corrected marker set and runs the scale tool again and the errors decrease significantly.

if it's not the way to reduce the errors then please tell me how?

Best regards.