| # NCSA meeting-room chair objects |
|
|
| One shared chair mesh, ten sessions, fifteen static instance poses. |
|
|
| - `assets/chair.obj`: the merged Blender chair geometry, in metres, Z-up, |
| recentered at its local bounding-box centre. Geometry and size are unchanged. |
| - `assets/chair.json`: shared asset ID, bounds/extent, mesh hash, source provenance, |
| and the translation back into the original Blender mesh-local coordinates. |
| - `sessions/<session>.json`: instance poses, quaternion, translation, local extent, |
| source matrices, and provenance. All instances reference the same mesh file. |
| - `manifest.json`: asset/session index. |
| - `sample_index.json`: existing processed clips mapped to the session annotations. |
| - `qc/index.html`: all ten sessions rendered back into their three cameras. |
| - `verification.json`: numerical consistency checks. |
|
|
| ## Instances and placement sources |
|
|
| | Sequences | Keys | Pose source | |
| |---|---|---| |
| | 1–5 | `chair` | Previously reviewed individual scene_1 fits | |
| | 6–10 | `chair` (near), `chair__2` (far) | User's unchanged `seq6.blend` placement, reused across the fixed setup | |
| |
| `source_instance` retains the earlier naming: near = `chair_1` / Blender `chair1`, |
| far = `chair_0` / Blender `chair2`. The two instances have separate object IDs and |
| the same `asset_id: ncsa/meeting_room/chair` and `category: chair`. |
| |
| Seq 4–15 use the same physical camera setup according to the user. Every supplied |
| calibration file anchors cam_01 with identity extrinsics and identical intrinsics; |
| per-session refinement of the other cameras does not itself establish a changed |
| cam_01 frame. Seq 6–10 therefore reuse the exact same two manual pose matrices, |
| under the stationary-chair assumption checked against the background overlays. |
| Seq 1–5 retain their own poses rather than assuming identical chair placement. |
| |
| ## Coordinate convention |
| |
| All saved object poses are in the **calibration / cam_01 world**, in metres: |
| X = camera right, Y = camera down, Z = camera forward. |
| |
| `mesh_to_world` uses column-vector convention: |
| |
| ```python |
| world_vertices = local_vertices @ matrix[:3, :3].T + matrix[:3, 3] |
| ``` |
| |
| The mesh is bounding-box centred. Consequently, `translation_xyz` is the world |
| position of its bounding-box centre, not the original Blender object origin. |
| `source_mesh_to_world` separately preserves that original pose. Recentering was |
| checked to leave all placed world vertices unchanged (tolerance 1e-7 m). |
| |
| `track` is a static length-10 vector: |
| `[qw, qx, qy, qz, tx, ty, tz, extent_x, extent_y, extent_z]`. |
| The extent is in the rotated object's **local axes**, not a world-aligned AABB. |
| `bbox_convention` is `local_extent_centered_at_track_translation`. |
| Repeat the vector over a clip's frame count when a `[T,10]` track is needed. |
| |
| These files are standalone object annotations. Existing sample PKLs, WDS shards, |
| human motion, and IMUs were not modified. In particular, do not concatenate these |
| camera-world tracks with the packed IMU-world motion without an explicit coordinate |
| conversion. `sample_index.json` provides sample-to-session bindings, not an implicit |
| conversion or loader integration. |
| |
| ## Reading an annotation |
| |
| ```python |
| import json |
| from pathlib import Path |
| import numpy as np |
| import trimesh |
| |
| root = Path('data/processed/ncsa/objects') |
| record = json.loads((root/'sessions/0915_scene_2_seq_6.json').read_text()) |
| obj = record['objects']['chair'] # near chair |
| mesh = trimesh.load(root/obj['mesh_path'], force='mesh', process=False) |
| mesh.apply_transform(np.asarray(obj['mesh_to_world'])) |
| ``` |
| |
| ## Quality and reproducibility |
| |
| The seq6 manual placement was accepted by the user after three-camera review. |
| Its remaining mesh/seat/caster discrepancies are preserved; this release does not |
| claim independently measured geometric ground truth. No scale fitting, deformation, |
| or additional alignment was applied during publication. QC includes chair-to-chair |
| occlusion but not occlusion by other room geometry. |
| |
| From the IMU4D_dev root, reproduce into a **new** output directory: |
| |
| ```bash |
| OPENBLAS_NUM_THREADS=1 OMP_NUM_THREADS=1 \ |
| python -m dataset_process.ncsa.export_chair_objects --out <new-output-directory> |
| ``` |
| |
| The export refuses to overwrite an existing release. The source `.blend`, previous |
| fit results and original chair mesh are retained. |
| |
