Markerless motion capture and sports biomechanics.
A foundational overview: marker-based vs markerless pose estimation, the OpenPose/MediaPipe/MeTRAbs coordinate systems, ~10 degree accuracy and why errors happen, kinematics vs kinetics, capture frameworks, and a single-camera to OpenSim example.
The math behind atan2d(det, dot): the determinant is the cross-product magnitude (|a||b|sin), the dot product is |a||b|cos, so their ratio is tan – and why the two-argument atan2 preserves sign and handles angles beyond 90 degrees.
A step-by-step MATLAB walkthrough: import OpenPose JSON, compute joint angles with atan2d, filter with Butterworth (cutoff from the power spectrum), find phases and landing, and export a results table.
Breaking a football kick down phase by phase with a slow-motion phone video and OpenPose – backswing, leg cocking, acceleration, and the supporting leg’s shock absorption and energy transfer, read from the joint-angle and angular-velocity curves.