Update dataset card and overview image

README.md

@@ -27,6 +27,8 @@ configs:
 
 # SparseVideoNav Datasets
 
+![SparseVideoNav dataset overview](assets/dataset_mosaic.png)
+
 This repository contains the real-world navigation datasets released with [OpenDriveLab/SparseVideoNav](https://github.com/OpenDriveLab/SparseVideoNav):
 
 - **BVN**: Beyond-the-View Navigation.
@@ -42,10 +44,15 @@ Project links:
 
 SparseVideoNav studies real-world vision-language navigation with sparse future video generation. The datasets contain language instructions, RGB frame sequences, and low-level navigation actions. The number of actions matches the number of RGB frames for every released episode.
 
-| Subset | Episodes | RGB frames | Task |
-| --- | ---: | ---: | --- |
-| `bvn` | 5,417 | 695,373 | Beyond-the-View Navigation |
-| `ifn` | 5,625 | 712,290 | Instruction-Following Navigation |
+Due to policy restrictions, this public release contains the policy-compliant subset of the collected real-world data. At the released sampling rate of **4 fps**, the open-sourced subset contains **about 98 hours** of navigation data.
+
+| Subset | Episodes | RGB frames | Duration @ 4 fps | Task |
+| --- | ---: | ---: | ---: | --- |
+| `bvn` | 5,417 | 695,373 | 48.29 h | Beyond-the-View Navigation |
+| `ifn` | 5,625 | 712,290 | 49.46 h | Instruction-Following Navigation |
+| **Total** | **11,042** | **1,407,663** | **97.75 h** | - |
+
+Duration is computed as `num_frames / 4 / 3600`.
 
 ## Repository Structure
 
@@ -54,6 +61,8 @@ Images are stored in compressed tar shards to avoid hundreds of thousands of sma
 ```text
 .
 ├── README.md
+├── assets/
+│   └── dataset_mosaic.png
 ├── bvn/
 │   ├── annotations.json
 │   ├── data.jsonl
@@ -72,13 +81,36 @@ Images are stored in compressed tar shards to avoid hundreds of thousands of sma
         └── ...
 ```
 
-Each line in `bvn/data.jsonl` or `ifn/data.jsonl` is an episode-level JSON object. Important fields:
-
-- `episode_id`: episode identifier.
-- `instruction` / `instructions`: natural-language navigation instruction.
-- `actions`: per-frame low-level action sequence with `dx`, `dy`, and `dyaw`.
-- `frame_files`: RGB frame paths inside the shard after extraction.
-- `shard`: shard file containing the episode frames.
+## Data Format
+
+Each line in `bvn/data.jsonl` or `ifn/data.jsonl` is an episode-level JSON object.
+
+| Field | Type | Description |
+| --- | --- | --- |
+| `dataset` | string | Dataset subset name, either `bvn` or `ifn`. |
+| `subset` | string | Release subset marker. The current public release uses `main`. |
+| `episode_id` | string | Unique episode identifier. |
+| `instruction` | string | Primary natural-language navigation instruction. |
+| `instructions` | list[string] | Instruction list. Current records contain one instruction. |
+| `task_type` | string | Task label, e.g. `beyond_the_view_navigation` or `instruction_following_navigation`. |
+| `split` | string | Dataset split. Current release uses `train`. |
+| `image_dir` | string | Original relative episode image directory before sharding. |
+| `rgb_dir` | string | Original relative RGB frame directory. |
+| `num_frames` | integer | Number of RGB frames in the episode. |
+| `num_actions` | integer | Number of low-level actions. This matches `num_frames`. |
+| `actions` | list[object] | Per-frame low-level navigation actions. Each action has `dx`, `dy`, and `dyaw`. |
+| `annotation_file` | string | Annotation file path in this repository. |
+| `frame_files` | list[string] | RGB frame paths inside the shard after extraction. |
+| `asset_dirs` | list[string] | Original episode asset directories included in the shard. |
+| `shard` | string | Tar shard containing the episode frames. |
+
+Each action object contains:
+
+| Field | Type | Description |
+| --- | --- | --- |
+| `dx` | float | Relative forward/backward displacement for the corresponding step. |
+| `dy` | float | Relative lateral displacement for the corresponding step. |
+| `dyaw` | float | Relative yaw change for the corresponding step. |
 
 Example:
 
@@ -95,6 +127,8 @@ Example:
 }
 ```
 
+`annotations.json` stores the original annotation records with the core fields `id`, `video`, `actions`, and `instructions`. `shard_manifest.jsonl` stores shard-level metadata, including the shard path, episode ids, raw byte size, compressed byte size, frame count, and file count.
+
 ## Usage
 
 Load episode metadata with Hugging Face Datasets: