feat(schema): load 0.x datasets as 1.0 records (core tables and labels)

docs/schema/v1/index.md

@@ -131,3 +131,27 @@ Provenance {
   "process_config_version_id":  <option[int]> -- Web.Auto processing configuration version.
 }
 ```
+
+## Loading 0.x Datasets
+
+`load_dataset()` reads a 0.x dataset (no `manifest.json`) by converting its tables to 1.0 records when loading, on a best-effort basis. Sensor data files stay as they are: one file per frame, and `sample_data.frame_index` is `null`.
+
+Every 0.x frame becomes a `sample`: the files of all channels with the same frame number (e.g. `00042.jpg` and `00042.pcd.bin`, as the 0.x converter names them) form one frame. 0.x samples, which are annotated frames only, keep their tokens; 0.x samples of the same frame (one per camera image in camera-only datasets) are merged into the earliest one. A frame with a 2D label is a key frame.
+
+Each 0.x `calibrated_sensor` row becomes a `sensor` row, keeping its token. The camera block takes its intrinsics and distortion from it, its size from `sample_data`, and the distortion model from the number of coefficients (0: `none`, 5: `plumb_bob`, 8: `rational_polynomial`). The LiDAR block is described from the first frame. Map `sha256` and `projector` are read from `map/lanelet2_map.osm` and `map/map_projector_info.yaml`.
+
+Labels are `manual` unless 0.x marks them as autolabel (`provenance` = model names). `surface_ann` rows become `object_ann` rows without an instance, with `bbox` computed from the mask. 0.x visibility `unavailable` (or any unknown level) becomes `visibility_token: null`, and the aliases `v0-40`, `v40-60`, `v60-80`, `v80-100` map to `none`, `partial`, `most`, `full`.
+
+1.0 requires some values that 0.x never stored. They are filled with these placeholders (`V0Converter.FALLBACKS`), which keep the dataset loadable but say nothing about it. In particular, `vehicle.model == "unknown"` means the vehicle dimensions are placeholders and must not be used, and `"unknown"` map IDs mean the map is not identified:
+
+| Table / block   | Field                                                 | Placeholder                                                                                         |
+| --------------- | ----------------------------------------------------- | --------------------------------------------------------------------------------------------------- |
+| `vehicle`       | `model`                                               | `"unknown"`                                                                                         |
+| `vehicle`       | `length`, `width`, `height`, `wheel_base`             | `1.0`                                                                                               |
+| `vehicle`       | `name`                                                | 0.x `log.vehicle`, `null` if empty                                                                  |
+| `map`           | `map_id`, `version_id`                                | `"unknown"`                                                                                         |
+| `map`           | `source`                                              | `"webauto"`                                                                                         |
+| `ego_pose`      | `source`, `frame`                                     | `"localization"`, `"map"`                                                                           |
+| `sensor.camera` | `is_rectified`                                        | `true`                                                                                              |
+| `sensor.lidar`  | `frame_id`, `is_undistorted`, `container.compression` | `"base_link"`, `true`, `"none"`                                                                     |
+| `sensor.lidar`  | `fields` (`.bin`)                                     | `x y z intensity channel return_type time_stamp`, cut to `num_pts_feats` (default 5), all `float32` |

docs/schema/v1/table.md

@@ -316,7 +316,7 @@ attribute {
 
 - Filename: `visibility.json`
 
-Unchanged from 0.x.
+Unknown visibility is `sample_annotation.visibility_token: null`; the 0.x level `unavailable` is dropped.
 
 ```json
 visibility {
@@ -360,7 +360,7 @@ sample_annotation {
   "sample_token":     <str> -- Foreign key to the `Sample` table.
   "instance_token":   <str> -- Foreign key to the `Instance` table.
   "attribute_tokens": <[str;N]> -- Foreign keys to the `Attribute` table.
-  "visibility_token": <str> -- Foreign key to the `Visibility` table.
+  "visibility_token": <option[str]> -- Foreign key to the `Visibility` table. `null` if unknown.
   "translation":      <[float;3]> -- Box center in meters.
   "size":             <[float;3]> -- (width, length, height) in meters.
   "rotation":         <[float;4]> -- Quaternion (w, x, y, z).

t4_devkit/common/io.py

@@ -16,7 +16,11 @@
 if TYPE_CHECKING:
     from t4_devkit.typing import PathLike
 
-__all__ = ("load_json", "save_json", "load_pointcloud", "load_image")
+__all__ = ("load_json", "save_json", "load_pointcloud", "load_image", "V0_BIN_FIELDS")
+
+# 0.x `.bin` layout: this list cut to `num_pts_feats`, all float32 (as written by the converter).
+# `.bin` stores no names; these are the 1.0 names (0.x calls `channel` "ring"), all float32.
+V0_BIN_FIELDS = ("x", "y", "z", "intensity", "channel", "return_type", "time_stamp")
 
 
 def load_json(filename: PathLike) -> Any:

t4_devkit/dataclass/pointcloud.py

@@ -9,7 +9,7 @@
 import numpy as np
 from attrs import define, field
 
-from t4_devkit.common.io import load_json, load_pointcloud
+from t4_devkit.common.io import V0_BIN_FIELDS, load_json, load_pointcloud
 from t4_devkit.common.timestamp import Stamp
 
 if TYPE_CHECKING:
@@ -31,9 +31,6 @@
 # Point fields of `LidarPointCloud.points`, in row order.
 XYZI = ("x", "y", "z", "intensity")
 
-# 0.x `.bin` layout: this list cut to `num_pts_feats`, all float32 (as written by the converter).
-V0_BIN_FIELDS = ("x", "y", "z", "intensity", "ring", "return_type", "time_stamp")
-
 
 @define
 class PointCloudSourceInfo:

t4_devkit/schema/v1/__init__.py

@@ -2,6 +2,7 @@
 from .attribute import *  # noqa
 from .caption import *  # noqa
 from .category import *  # noqa
+from .convert_v0 import *  # noqa
 from .ego_pose import *  # noqa
 from .instance import *  # noqa
 from .keypoint import *  # noqa