Expand dataset card: provenance, depth stats, DA3 round-trip, citation

README.md

@@ -20,13 +20,17 @@ size_categories:
 
 A small, fast-to-download slice of the Structured3D synthetic indoor dataset,
 converted to a uniform posed-RGB-D format for quick model test-runs. This is a
-**subset** of the full set: **100 scenes** (randomly sampled, seed 0) from
-collection `00`, using the pre-rendered **`full`** (furnished) perspective views.
-Across the 100 scenes there are **2,198 frames** (3–49 per scene).
+**subset**: **100 scenes** (randomly sampled, seed 0) from collection `00`, using
+the pre-rendered **`full`** (furnished) perspective views. Across the 100 scenes
+there are **2,198 frames** (3–49 per scene).
 
 These are photorealistic synthetic renders with **perfect dense ground-truth
 depth** and exact camera poses — no reconstruction or pseudo-labelling involved.
 
+This subset is part of a family of uniformly-formatted posed-RGB-D test-run
+datasets: see also `3dvlm-replica_subset`, `3dvlm-hm3d_subset`, and
+`3dvlm-taskonomy_subset` (same on-disk layout and conventions).
+
 ## Contents
 
 100 scenes, one `.tar` each under `structured3d/`. Each tar extracts to a scene
@@ -53,13 +57,31 @@ in the same order as `meta.json`'s `frame_ids` and the sorted `images/` files.
 ## Conventions
 
 - **Coordinate frame:** OpenCV (x-right, y-down, z-forward). `extrinsics` is the
-  **world→camera (w2c)** matrix; invert it for camera→world.
+  **world→camera (w2c)** matrix; invert it for camera→world. The translation is in
+  **metres** (the source millimetre world is rescaled on conversion).
 - **Depth:** projective **z-depth in metres** (distance along the camera z-axis,
-  not Euclidean ray length). Decoded from the source 16-bit mm depth (`÷1000`);
-  invalid pixels (source value `0`) are zeroed — use `valid_mask` to ignore them.
+  not Euclidean ray length). Decoded from the source 16-bit millimetre depth
+  (`÷1000`); the source is already planar z-buffer depth, so **no Euclidean→z
+  cosine correction is applied**. Invalid pixels (source value `0`) are zeroed —
+  use `valid_mask` to ignore them. Typical valid coverage is **≈99.5%**, with
+  depths in roughly the **0.05–7 m** range.
 - **Intrinsics:** **per-frame** pinhole `K`, reconstructed from each frame's
   horizontal/vertical field of view (separate `fx`/`fy`, principal point centred).
-  Image size is 720×1280 (H×W).
+  Image size is 720×1280 (H×W). The reconstructed `(K, w2c)` are verified to
+  round-trip through the project's ray-map (DA3) convention.
+
+## Source & provenance
+
+Built from the official **Structured3D perspective `full`** renders, collection
+`00` (`Structured3D_perspective_full_00.zip`). Only three files per frame are used:
+`rgb_rawlight.png` (the RGB modality in the full-perspective zip is
+`rgb_rawlight.png`, **not** `rgb.png`), `depth.png`, and `camera_pose.txt`. Camera
+poses come straight from `camera_pose.txt` (eye / view-dir / up / half-FOVs), built
+into a right-handed look-at and converted to OpenCV `w2c`. No depth model or
+pseudo-labelling is involved — depth and poses are the renderer's exact values.
+
+There is no separate "full" mirror of this conversion; this 100-scene slice of
+collection `00` is the published extent.
 
 ## Quick start
 
@@ -72,12 +94,31 @@ tarfile.open(p).extractall("structured3d/")
 
 meta  = json.load(open("structured3d/scene_00000/meta.json"))
 depth = np.load("structured3d/scene_00000/depth.npy")        # (N, 720, 1280)
+mask  = np.load("structured3d/scene_00000/valid_mask.npy")   # (N, 720, 1280)
 K     = np.load("structured3d/scene_00000/intrinsics.npy")   # (N, 3, 3)
 w2c   = np.load("structured3d/scene_00000/extrinsics.npy")    # (N, 4, 4)
+
+# Back-project frame 0 to a camera-frame point cloud (metres):
+H, W = meta["image_size"]
+fx, fy, cx, cy = K[0,0,0], K[0,1,1], K[0,0,2], K[0,1,2]
+ys, xs = np.mgrid[0:H, 0:W]
+z = depth[0]
+X = (xs - cx) / fx * z
+Y = (ys - cy) / fy * z
+pts = np.stack([X, Y, z], -1)[mask[0]]   # (M, 3) valid points
 ```
 
-## License
+## License & citation
 
 Built on [Structured3D](https://github.com/bertjiazheng/Structured3D), released for
 **research use only** under its original data agreement; the same terms apply to
-this derived subset. Please cite the original Structured3D paper if you use this data.
+this derived subset. If you use this data, please cite the original paper:
+
+```bibtex
+@inproceedings{Structured3D,
+  title     = {Structured3D: A Large Photo-realistic Dataset for Structured 3D Modeling},
+  author    = {Zheng, Jia and Zhang, Junfei and Li, Jing and Tang, Rui and Gao, Shenghua and Zhou, Zihan},
+  booktitle = {Proceedings of The European Conference on Computer Vision (ECCV)},
+  year      = {2020}
+}
+```