What "Accurate" Means For a Joint Angle
A percentage without a tolerance is not a claim. The full scorecard for a video biomechanics system, by configuration, and why 10 degrees settles it.
Biomechanics from Video01
Series · 8 parts · 2,026–2,026
Biomechanics from Video
The measurement programme behind Athlete Intelligence: what "accurate" means for a joint angle, why 2D beat 3D on the angles that matter, how a camera can be taught to grade its own footage, and what the system refuses to measure. Every figure is one I measured, including the ones that came out badly.
From Pixels to a Knee Angle
The whole monocular pipeline for one number, and what the detector's pixel error costs once you express it in degrees instead of in average precision.
Biomechanics from Video02
Why 2D Beat 3D on the Angles That Matter
Lifting one camera to 3D sounds strictly better than measuring in the image plane. On sagittal flexion it is worse, and the reason is a free parameter.
Biomechanics from Video03
Facing, Sign, and the Error That Mirrors Everything
Which way an athlete faces sets the sign of every sagittal angle at once. One bit, 100 out of 100 on 919 comparisons, and why sign errors are not small.
Biomechanics from Video04
Teaching a Camera to Grade Its Own Footage
Camera obliquity is invisible to one lens, so the system infers it from anatomy. Banding its own error by that estimate beats banding by ground truth.
Biomechanics from Video05
Triangulation, and How Many Cameras You Actually Need
The multi-view path: DLT in enough detail to implement, how many cameras earn their place, and three lessons about evaluating a solver whose truth you cannot see.
Biomechanics from Video06
What the System Refuses to Measure
Three measured refusals in a markerless movement pipeline, the gaps that are still open, and why a clinician should prefer software that says not measured.
Biomechanics from Video07
Kinetix: An Agent Harness Inside a Clinical System
Sixty tools, twenty-nine of them mutating, inside a system holding injury records. The Go that enforces one rule: the agent inherits the caller.
Biomechanics from Video08