Hi,
I have been running OpenSim so I can calculate joint reaction forces to then time with gait events. However, I am noticing that beginning at the CMC step, the output frequency is incredibly variable, making it hard for me to coordinate time stamps.
My RRA data gives output in 0.001 s increments, giving a nice 1000 Hz frequency. However, once I run through the CMC step, the frequency changes.
For example, the CMC output starts at 0.03s (frame 1), then progresses to 0.030041s (frame 2), then 0.030284s (frame 3) and so on, sometimes making jumps by >0.001s. This means that the output frequency can vary anywhere between 25,000 and 888 Hz between frames. This carries over into the joint reaction step as well, so I am having trouble trying to sync this back with other data.
I have minimized the amount of data to ~1s and tried altering the input kinematics filter, all without effect. I have not yet played with the integrator settings, but would that help to address the problem?
Has anyone else run into this and can offer a solution?
Thanks!
Dan
Variable Frequency of CMC Output
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Edward Syrett
- Posts: 34
- Joined: Mon Jan 14, 2019 11:04 am
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Edward Syrett
- Posts: 34
- Joined: Mon Jan 14, 2019 11:04 am
Re: Variable Frequency of CMC Output
In case anyone runs into the same issue, I ended up resampling the joint reaction force in Matlab to 1000hz. If anyone needs help with that, let me know!
Dan
Dan
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Ayman Habib
- Posts: 2252
- Joined: Fri Apr 01, 2005 12:24 pm
Re: Variable Frequency of CMC Output
Hi all,
For tools that perform integration like CMC, Forward, the result files are updated once per successful integration step and as such are not uniformly sampled. Keep in mind that if you have events (e.g. contact start/end) then you may miss some important steps if you stick with uniform time sampling, or you may end up smoothing it out unintentionally. There're low level event reporters that allow for customization of reporting but they are not utilized by the tools at the moment.
Hope this helps,
-Ayman
For tools that perform integration like CMC, Forward, the result files are updated once per successful integration step and as such are not uniformly sampled. Keep in mind that if you have events (e.g. contact start/end) then you may miss some important steps if you stick with uniform time sampling, or you may end up smoothing it out unintentionally. There're low level event reporters that allow for customization of reporting but they are not utilized by the tools at the moment.
Hope this helps,
-Ayman