which two coordinate systems are represented by R_{Ti}

[chen4011]

Hello, I'm using your imu-human-pose-pytorch project and I'm hoping to input measurement data myself. However, I'm encountering issues with rotation matrices when doing so.

I'd like to ask, in the TotalCapture-Toolbox project, which two coordinate systems are represented by R_{Ti}? From the section (3.4) implementation details of the paper "Real-Time Full-Body Motion Capture from Video and IMUs" referenced by the authors of the TotalCapture dataset, we understand that R_{ig} is assumed to be consistent between IMUs and aligned with the world coordinates through the global up direction and magnetic north. Despite this, I'm still unable to understand which two coordinate systems RTi represents the transformation matrix for. Therefore, I'd like to ask for clarification from everyone. Thank you!