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Noise in GRF file

Posted: Mon Dec 23, 2019 10:53 am

by gnapikatalluri

Hi everyone,

I am new to OpenSim. I extracted .trc and .mot files from the .c3d file using MATLAB code. When I previewed the motion file, I observed there is a lot of noise in the ground reaction force (As shown in the below figure). How can I remove the noise?

: noiseGRF.png (286.32 KiB) Viewed 243 times

Thanks in advance!

Gnapika

Re: Noise in GRF file

Posted: Mon Dec 23, 2019 12:24 pm

by bogert

This is noise in the center of pressure (COP). The center of pressure is calculated from the force plate's load cells, and is undefined (zero divided by zero) when the force is zero. See eq. [3] in http://www.kwon3d.com/theory/grf/cop.html

It won't affect any mechanical analysis, only the visualization.

Some visualization systems have an option to turn the force visualization off when the force is below a certain threshold. If Opensim does not have this option, that might be a useful feature to consider.

Ton van den Bogert