Data model

• Keypoints (core/data_primitives/keypoints.py), named points: .names tuple, .xyz (N, 3) (x,y in pixels; z filled by triangulation later), .visibility (N,) scores in 0-1. Undetected points are NaN with visibility 0. Provides name-based lookup, slicing, concatenation, confidence masking, and translation.
• BoundingBox, x1y1x2y2 plus confidence, with crop/clamp/scaling helpers.
• StageObservation / Observation (core/data_primitives/observation.py), per-frame result. observation.stages["name"].keypoints returns a stage's Keypoints; children nest under .children. Observation.to_keypoints() flattens the whole stage tree into one Keypoints with <stage>.<point> name prefixes, the docstring calls this "the form passed to FreeMoCap for triangulation."
• TrackerState (core/tracker/tracker_state.py), the explicit external temporal state: per-stage StageState holding bbox smoothing state, per-detector keypoint filter states, last keypoints, and consecutive miss/reset counters.