Theia3D is a markerless motion capture software that estimates 3D human pose from multiple synchronized 2D camera views using deep learning algorithms.

After using a calibration method to determine the position and orientation of every camera in the camera system, deep learning algorithms are applied to the videos on a frame-by-frame basis to identify and track over 120 landmarks on the visible humans in the 2D videos. Using the camera system calibration parameters, those landmark detections from multiple 2D videos are then triangulated into 3D landmark positions, and a skeletal model is scaled and optimized to track the motion of those landmarks. This scaled skeletal model made up of 17 rigid segments represents the 3D pose estimates of the tracked people within the videos, from which numerous kinematic biomechanical signals can be obtained.