force plate data

[Maryam Hajizadeh]

Hey all,

I had 2 force plates for my measurements. Now, I exported the force plate data as .CSV files. However, the results in csv files are not the same as ones that are shown in VICON graphs. The magnitude are somehow the same, but the sign (negative/positive) are sometimes different, espesially for my 2d force plate. Does anyone know what can be the reason and are csv files now reliable to use?


Thanks.
Maryam Hajizadeh

[Patrick Varady]

Re: force plate data

Hi Maryam,

I believe that Vicon will automatically display all the data in the same coordinates system independent of how the actual force plate coordinate systems are arranged. So I guess you need to have a look at actual coordinate systems of the force plates, very often they are not aligned in the direction (physically). It is also possible that there are to different force data included, one is named analog data and given in the force plates' coordinate system and the other automatically adjusted force data.

Best regards,
Patrick

[Maryam Hajizadeh]

Re: force plate data

Thanks a lot Patrick.

The graphs that are shown in VICON are based on the global coordinate system or force plate coordinate system?

Then for my kinetic analysis, I should not work with analog data, right?

[Edmund Cramp]

Re: force plate data

... are csv files now reliable to use?

.CSV (commas separated value) files are reliable as a format for converting binary data to ASCII so that the data can be accessed - however the problem is that there is no standard for the information that is transferred to the CSV files. I think that this is the problem here - you have force data in the CSV file but nothing to indicate which direction the subject walked over the plate. The direction that the subject walks will affect all of the data - but most obviously fore-aft shear.

[Patrick Varady]

Re: force plate data

Maryam, if you are using the plug in gait model you can find more information (e.g. angles and their coordinate systems) here:

http://wweb.uta.edu/faculty/ricard/Classes/KINE-5350/PIGManualver1.pdf

The analog data is usually unfiltered while the force plate data might have already undergone some kind of filtering. But maybe this information is not correct for your system's configuration. Depending on what you are doing you can chose either one. AnyBody for example will use the analog data.