What metrics does Mocap tool box convert Force Plate values (Forces, COP Moments) to?

I am using this guide and MocapTools to visuliaze Vicon motion and Kistler force plate data:https://blog.jcamargo.co/tutorials_mocaptools_plot/

I have the animation running and have use some code to generate the force values, but in the guide, when I extract and transform the Force Plate values like this

fp=Vicon.C3DtoMOT('C:\Users\MYPATHWAY\ReachMiddle.c3d');%Have hidden actual pathway here
%transform from Osim (default) to Vicon coordinates
fp{:,2:end}=Vicon.transform(fp{:,2:end},'ViconXYZ');

My fp table shows these values

But my original Vicon Ascii export (Excel file) shows different values in rows 5 to 10 of the fp table (i.e. the fp table changes them).

I realise the Osim toolbox applies a transformation, but I wondered why the values change so much and if anyone knows what they are being converted to as I want to make sure they accurately represent the raw data.

Answer 1

[Vidip]

The differences you observe between the values in your original Vicon ASCII export and the transformed fp table are due to coordinate system transformations applied by the MocapTools/Osim toolbox. Motion capture and force plate systems can use different coordinate conventions (for example, Vicon’s XYZ vs. OpenSim’s XZY).

When you run 'Vicon.transform(fp{:,2:end},'ViconXYZ')', the toolbox is converting the data from the OpenSim (Osim) coordinate system back to the Vicon convention, which can significantly change the numeric values, especially for axes that are swapped or inverted.

Please refer to the below link for more information:

• https://blog.jcamargo.co/tutorials_mocaptools_plot/

[Paul]

Cheers for the response, and yes, that was the blog I was following as mentioned in my original post, but my concern was are the force values still accurate after OpenSim converts them back to the Vicon convention.

I was trying to find the original values I could compare agaist to check, although as MoCapTools takes them straight from the C3d file before any transformations, the ASCII values are probably not the same.

Is this the best toolbox to use to model and plot Vicon and force plate (Kistler, not intergrated) data in your opinion?