.trc file coordinates origin

[Sergio Lemus]

Hello,

I have a question regarding the .trc file from OpenCap. We are trying to compare two markers (e.g., the right shoulder and right toe) to see if they are aligned along the frontal axis (Z coordinate) when a person lands from a drop vertical jump. My approach is to check whether the Z-coordinate values for the shoulder (RShoulder) and toe (RBigToe) approximately match.

I found in some forum responses the socket 'parent_frame,' as well as the fixed location expressed in its parent frame (x, y, z coordinates), applies to the marker data of the model (https://github.com/stanfordnmbl/opencap ... enpose.xml). At first, I assumed the coordinate values in the .trc file (Post-Augmentation) followed the respective socket parent frame as their origin. However, after reviewing some of my own recordings, it seems more likely that they use a global coordinate system.

Am I correct in assuming this? Do all markers in the .trc file follow a single origin (0,0,0)?

Any additional suggestions you may have would be greatly appreciated.

[Antoine Falisse]

Hey, yes the marker data are expressed in the world frame.