Feet moving up and down during simulation (not staying in contact with the ground)

[Erica Beaucage-Gauvreau]

Hi,

During my simulations, the subject is squatting down and I notice that the feet are moving up and down by about 4-5 cm. I tried increasing the tracking weights on the feet (especially relative to the pelvis) but the model is still moving up and down. I don't want to decreased the weighting on the pelvis/sacrum too much because I am looking at back angles so it is important to track the pelvis closely as well.

Here is an illustration of the calc marker errors when the model is moving down:

calc markers.JPG (18.83 KiB) Viewed 257 times

What could be done to reduce this movement, and thereby reduce the IK errors?

Thank you,

Erica

[Thomas Uchida]

A couple ideas come to mind. First, you mentioned that you're interested in back angles. How sensitive will your analysis of the back be to errors at the feet? It looks like the tracking of the feet could be improved, but it may not be critical for your research question. Aside from the animation, what metrics are you using to determine whether your model is adequate? Secondly, IK seeks the minimum weighted sum of squared marker errors at each time frame, so perhaps the tracking error of the foot markers is being "diluted" by (a) high weights on other markers in the model and/or (b) simply a large number of other markers with moderate weights. Finally, if the error you're seeing is too large, it may be necessary to revisit the scaling step and/or adjust the placement of markers on the model.