FP Coordinates

Vishal R · Post by **Vishal R** » Wed Jun 24, 2015 9:40 am

Thank you for the release of v.2.2. This have made life easier for data extraction from c3d files. I have a confusion on what coordinate system to be used for rotation of the Force plates in the laboratory setup.

I have made my own laboratory setup file for acquisition. The coordinate system being used in the laboratory is defined as : <CoordinateSystemOrientation>YZX</CoordinateSystemOrientation>

This have been given as per the guidelines in the user manual. Now for defining the coordinates of FP, should I consider this (YZX) as my global coordinate or should I consider the OpenSim coordinates (XYZ) as global coordinates for the rotations defined inside <FPtoGlobalRotations>

I was using my laboratory coordinate as the global coordinate and rotated the force plates with respect to that. While performing the RRA in OpenSim my model was sinking downwards and the masses suggested for body segments are in negative. This raised the suspicion whether it could be due to the incorrect definition of coordinates to FP in data acquisition. It would be really great if your help me figure it out.

Alice Mantoan · Post by **Alice Mantoan** » Mon Jul 20, 2015 4:16 am

Dear Vishal,

I'm sorry for the late answer in this Forum.

As I have already replied to the email you sent me, for defining the coordinates of FP inside <FPtoGlobalRotations>, you must consider your laboratory global coordinate system. Rotations to OpenSim are automatically computed from the orientation of your laboratory global coordinate system.

I regret to inform you that you problem should not be related to this. Definition of FP coordinate systems is not accounted into OpenSim, you can check the mot file for this. If the mot file is correct with respect to your marker file, then your data have been properly processed.

Hope you have solved your issue with RRA.
Best regards,
Alice

FP Coordinates

FP Coordinates

Re: FP Coordinates