metadata/definitions/conventions.md

Conventions

• World frame: Z-up, metres, levelled per Nokov capture block; z = 0 at the Nokov origin. Per-session details in meta.json under canonical.
• Time: seconds, t = 0 at the first solved Body0 frame. Every stream keeps its own t; nothing is resampled.
• Quaternions: xyzw, global orientation in the world frame.
• Poses: 4x4 homogeneous T_world_<x> maps points from frame into the world frame.
• valid masks mark frames with a usable value; invalid frames may hold NaN.
• Merged npz files prefix keys by source: left_, right_, rig_, tracker_, or the video name (head_left_t, wrist_right_frame_index, ...).
• Objects: motions/objects.npz (all object instances on the body grid), see objects.md.
• Hands: motions/smplx.npz carries finger articulation from GSI hand tracking on the mocap body wrist (hand_observed, hand_quality_deg). motions/hands_mano.npz is the hand tracking alone at 30 Hz: native MANO per side (flat_hand_mean=True, axis-angle), 21 joints in the world and in the left_front OpenCV camera frame, placed with the mocap head pose; usable and body_consistent (wrist within 100 mm / 30 deg of SMPL-X) masks. Its convention key has the details.
• SLAM: cameras/slam.npz is GSI's visual-inertial SLAM of the left_front camera as delivered (T_slam_cam) and rigidly aligned to the world (T_world_slam, T_world_cam), with ATE against the mocap head in metrics_json.
• raw/ holds vendor files unchanged: Nokov exports (bvh/csv/trc, millimetres, Y-up) and device sqlite (.db).