simtk.org

I am trying to use OpenSim to determine muscle forces. My data is currently in Visual 3D as a c3d file. I am using two force plates. my lab coordinate system in Visual 3D has the subject walking in +Y and +Z is up. I have tried to follwo the tutorials but the process always fails at some point. THe problems are: 1.foot position is backwards when I open motion file in OpenSim, 2. when I run RRA my subject "falls" downward through what would be the floor instead of walking forward, and 3. I cannot compute CMC.

Has anyone been able to export from Visual 3D to OpenSim....if so can you offer some advice or Help

Thanks
Erin

Hi Erin,

I have developped a toolbox that does exactly that: extracts data from a c3d file into a format suitable for OpenSim. It runs in Matlab (so you need that on your computer). It is easy to set up for any lab configuration and contains a full manual and examples. Once it is set up for your lab coordinate system, you can then batch process as many trials as you want into OpenSim.

https://simtk.org/home/c3dtoolbox

Tim

Thanks Tim...I'll give it a try and let you knkow what happens!

Erin

Erin,

I have experienced the same problems when using the export function from Visual3D to OpenSim. To help solve your two problems:

1. Recheck your model in Visual 3D to make sure your foot is in the correct plane. It may appear correct within the Visual 3D model window, but if the coordinates are incorrect, that is how it will be imported.

2. You are going through the floor because your motion is producing forces that are not accounted for in the actuators. Try to gradually increase the excitation values within the Actuator files (RRA & CMC) until you get the correct motion.

We do a lot of studies on sprinting, cutting, and jumping tasks and have to greatly increase our actuator values, otherwise the model can end up going through the floor or appear as though they stepped on a land mine.

Let me know if these help.