Contact force estimation (static optim.) OpenSim 4.0

[Felix Laufer]

Hi everyone,

I know that there is the following plugin for estimating contact forces, e.g. ground reaction forces, within the static optimization routine:
https://simtk.org/projects/statopt-contact.
However, it doesn't work with the recent OpenSim 4.0 version out of the box.
Is there a similar contact force estimation feature already included in OpenSim 4.0?
Otherwise, I guess it would be possible to adapt the plugin quite easily...

Thanks and best regards
Felix

[jimmy d]

I'm not sure what the plugin you mentioned actually does-- perhaps includes an optimization routine to adjust contact parameters-- but you don't need that to implement contact in OpenSim, it exists and is used pretty often.

Otherwise, I guess it would be possible to adapt the plugin quite easily...

That is not a good assumption. There have been many changes since 3.3 so, depending on what the plugin does, may have to be completely refactored.

If there isn't some specific reason to use 4.0, then you may want to use the 3.3 version so you can use the plugin.

[Felix Laufer]

Let me cite from the related paper:

In this contribution, we propose a parametric con-
tact model and formulate an associated force optimization problem to simultaneously estimate
unknown muscle and contact forces in an inverse dynamic manner from a prescribed motion
trajectory. Unlike existing work, we consider both the static and the kinetic regime of Coulomb's
friction law.

More precisely, I want to predict ground reaction forces during normal gait within the static optimization routine (with the assumption of an "efficient" muscle allocation), which I already did using AnyBody.
Now I'd like to reproduce the results with OpenSim. So, I guess there is no direct equivalent in OpenSim 4.0.
I think I'll start with the 3.3 version first and try to adapt the plugin later, if necessary.

[Felix Laufer]

I managed to update the code to OpenSim 4.0 and contacted the author of the plugin.
So, there is an updated version (contactForces4.0) on the project page that works with OpenSim 4.0: https://simtk.org/projects/statopt-contact