| # Conventions |
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| - 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 <x> 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). |
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