README.md

---
license: cc-by-4.0
tags:
- 3d-scene-graph
- functional-scene-understanding
- Embodied-AI
pretty_name: FunTHOR
size_categories:
- n<1K
language:
- en
---

# FunTHOR

📄 [Paper](https://arxiv.org/abs/2604.03696) | 🌐 [Project Page](https://funfact-scenegraph.github.io/)

**FunTHOR** is a synthetic dataset for **functional 3D scene understanding**, built on top of the
[AI2-THOR](https://ai2thor.allenai.org/) simulator. It provides part-level ground-truth geometry and
dense, rule-based **functional-relation annotations** (e.g. *knife slices apple*, *handle pulls to open
door*, *stove knob turns on/off burner*) for 12 indoor scenes, together with posed RGB-D
sequences for each scene.

The dataset was introduced as a benchmark in our work on constructing probabilistic, open-vocabulary
functional 3D scene graphs from posed RGB-D images. Compared to existing manually annotated datasets, FunTHOR is designed to provide **dense** annotations covering both **part–object** relations (a part operating its parent object) and
**object–object** relations (one object acting on another).

## Dataset at a glance

- **12 scenes** (kitchens, living rooms, bedrooms, bathrooms) selected from AI2-THOR.
- **621 ground-truth nodes** total (objects + functional parts), **92** of which are functional parts.
- **164 functional-relation edges** total, annotated by transparent, inspectable [rules](./annotation_rules/functional_relations_config.json).
- **60 posed RGB-D frames per scene** (1200×680), randomly sampled from reachable viewpoints.
- Object- and part-centric **point clouds** and an **object–part hierarchy** per scene.
- A **visible subset** per scene that retains only nodes/edges observable from the sampled RGB-D frames.

| Scene                 | nodes | parts | visible nodes | edges | frames |
|-----------------------|------:|------:|--------------:|------:|-------:|
| FloorPlan1_physics    |  117  |   32  |          113  |   45  |   60   |
| FloorPlan5_physics    |  111  |   29  |          107  |   45  |   60   |
| FloorPlan12_physics   |   76  |    6  |           73  |   12  |   60   |
| FloorPlan202_physics  |   26  |    1  |           25  |    4  |   60   |
| FloorPlan205_physics  |   39  |    1  |           39  |    5  |   60   |
| FloorPlan206_physics  |   34  |    1  |           34  |    3  |   60   |
| FloorPlan311_physics  |   41  |    3  |           41  |    8  |   60   |
| FloorPlan313_physics  |   31  |    1  |           31  |    3  |   60   |
| FloorPlan321_physics  |   28  |    1  |           28  |    3  |   60   |
| FloorPlan401_physics  |   34  |    1  |           34  |    8  |   60   |
| FloorPlan405_physics  |   40  |    6  |           37  |   12  |   60   |
| FloorPlan422_physics  |   44  |   10  |           43  |   16  |   60   |
| **Total**             | **621** | **92** |      **605** | **164** | **720** |

## Dataset structure

```bash
.
├── dataset_unique_labels.json       # all distinct object/part labels across the dataset
├── dataset_unique_relations.json    # all distinct functional-relation strings across the dataset
├── dataset_functional_labels.json   # labels that are categorized as functional elements for evaluation
├── annotation_rules/                # the rules used to auto-generate the functional edges (see below)
│   ├── functional_relations_config.json
│   └── manual_annotations/
│       └── FloorPlan*_physics.json
└── FloorPlan<ID>_physics/           # one folder per scene
    ├── node_list.pkl                # list of all ground-truth nodes (objects + parts)
    ├── object_metadata.json         # per-object metadata + object→parts hierarchy
    ├── annotations/                 # one JSON per node: maps node → point indices in pointcloud.ply
    │   └── node_XXXX_<Label>.json
    ├── annotations_aggregated.json  # all per-node annotations aggregated into one file
    ├── functional_relations.json    # ground-truth functional edges for this scene
    ├── pointcloud.ply               # dense scene point cloud (annotation indices reference this)
    ├── visible/                     # the visibility-filtered subset (see below)
    │   ├── node_list.pkl            # only nodes observable from the sampled frames
    │   └── visibility_stats.json    # per-node visible-point counts and visibility ratios
    └── dataset/                     # posed RGB-D capture for this scene
        ├── intrinsics.npy           # 3×3 pinhole camera intrinsics (shared by all frames)
        ├── color/000000.png … 000059.png   # RGB images, 1200×680, uint8
        ├── depth/000000.png … 000059.png   # depth images, 1200×680, uint16 (millimeters)
        └── pose/000000.npy … 000059.npy     # 4×4 camera-to-world matrices
```

### Nodes (`node_list.pkl`)

Each scene's `node_list.pkl` is a pickled Python `list` of node dictionaries. Each node is either a whole
object or a functional part. Fields:

| key        | type            | description |
|------------|-----------------|-------------|
| `node_id`  | int             | unique node index within the scene |
| `object_id`| int             | id of the owning object (a part shares its parent's `object_id`) |
| `label`    | str             | AI2-THOR label in UpperCamelCase, e.g. `StoveKnob`, `LightSwitch` |
| `is_part`  | bool            | `True` for functional parts (handles, knobs, buttons …), `False` for objects |
| `pcd`      | `(N, 3)` float64| points sampled on the node's mesh surface, in **world coordinates** (meters) |
| `colors`   | `(N, 3)` uint8  | per-point RGB |
| `center`   | `(3,)` float64  | centroid of `pcd` |

Nodes with label `Undefined` are placeholders and are typically skipped by loaders.

### Object metadata & part hierarchy (`object_metadata.json`)

A list of object records (one per `object_id`). Fields are `object_id`, `label`, `has_parts_annotation`,
and `parts` (the list of part labels belonging to the object). This encodes the object -> part hierarchy
referenced by the node list.

### Per-node point annotations (`annotations/`)

Each `annotations/node_XXXX_<Label>.json` maps a node to its supporting points **as indices into the scene's `pointcloud.ply`**:

```json
{ "node_id": 0, "object_id": 0, "label": "Tomato", "is_part": false, "point_indices": [50000, 50001, ...] }
```

`annotations_aggregated.json` contains the same information for all nodes in a single file.

### Functional relations (`functional_relations.json`)

A list of directed functional edges. Each edge connects a *subject* node (`first_*`) to an *object* node
(`second_*`):

```json
{
  "relation_type": "exact_match",
  "first_node_id": 40,  "first_object_id": 31, "first_label": "Faucet",
  "relation": "fill with water",
  "second_node_id": 96, "second_object_id": 68, "second_label": "Kettle"
}
```

`relation_type` is one of `exact_match`, `proximity_based`, `part_based`, or `manual_annotation`
(see *Annotation rules* below). Node ids reference `node_list.pkl`. The dataset-level
`dataset_unique_relations.json` lists all distinct `relation` strings.

### Visible subset (`visible/`)

Because some objects are never observed from the sampled viewpoints (e.g. items inside closed cabinets),
each scene also ships a **visibility-filtered** version intended for **evaluation**. `visible/node_list.pkl` holds the visible nodes and `visible/visibility_stats.json` records the
per-node visible-point counts and visibility ratios.

## Coordinate systems

**World / scene frame.** All node point clouds, centers, and `pointcloud.ply` are expressed in a single,
metric, **right-handed, Z-up** world frame (units: meters). Note this differs from AI2-THOR's native Unity convention
(left-handed, Y-up); the released data has already been converted to the Z-up right-handed frame above.

**Camera frame.** `dataset/pose/NNNNNN.npy` is a `4×4` **camera-to-world** transform `T_wc` (rotation has
determinant `+1`). The camera uses the **OpenCV convention**: `+x` right, `+y` down, `+z` forward (into the
scene).

**Intrinsics.** Shared `3×3` pinhole matrix for all frames. **Depth** PNGs are 16-bit and stored in **millimeters**
(divide by `1000` for meters); a depth of `0` denotes a missing/invalid measurement.

## Annotation rules (`annotation_rules/`)

The functional edges are produced **automatically and transparently** from a small set of inspectable rules,
rather than hand-labeled per scene. We include the exact rule configuration used to generate this release in
`annotation_rules/` so that the annotation logic is fully reproducible and auditable.

Each rule is a functional triplet `(first_label, relation, second_label)`. Rules are grouped by matching
strategy (`annotation_rules/functional_relations_config.json`):

- **`exact_match_relations`** — annotate an edge whenever a node's label exactly matches `first_label` and
  another node's label exactly matches `second_label` (e.g. *Knife → can slice or cut → Apple*;
  *Faucet → fill with water → Kettle*).
- **`proximity_based_relations`** — for each subject node, connect it to the **nearest** node matching
  `second_label`, provided the distance between centers is below a threshold (default 1 m, with optional
  per-rule `distance_threshold` overrides). Matching is greedy and globally distance-ordered so the result
  does not depend on rule ordering (e.g. *Faucet → run water into → Sink*; *Faucet → run water into → Bathtub*).
- **`part_based_relations`** — for objects with toggleable/openable AI2-THOR properties that expose explicit
  functional parts, connect the part to its parent object (e.g. *Lever → push down to start toasting → Toaster*;
  *Handle → pull to open → Door*).
- **manual annotations** — a few semantically ambiguous associations are recorded by hand in
  `annotation_rules/manual_annotations/<scene>.json` (currently only stove-knob → stove-burner pairings,
  with the relation *turn on/off*).

The functional-relation rule set was constructed by referencing the
[AI2-THOR object type documentation](https://ai2thor.allenai.org/ithor/documentation/objects/object-types),
in particular each object type's **Actionable Properties** (e.g. *sliceable*, *toggleable*, *openable*,
*fillable*), to decide which functional triplets are physically plausible.

## Credits and acknowledgements

- **Ground-truth meshes and scenes.** The object CAD models and AI2-THOR scenes used to generate FunTHOR's
  object- and part-centric ground-truth annotations come from the
  [hssd/ai2thor-hab](https://huggingface.co/datasets/hssd/ai2thor-hab) dataset (AI2-THOR–Habitat). We
  decomposed and re-annotated relevant assets into semantically meaningful parts to build the part-aware
  geometry. We gratefully acknowledge the HSSD / AI2-THOR–Habitat authors.
- **AI2-THOR.** Scenes and the simulation infrastructure are based on
  [AI2-THOR](https://ai2thor.allenai.org/) (Kolve et al., 2017).

## Citation

If you use FunTHOR, please cite our paper:

```bibtex
@inproceedings{Fu_2026_funfact,
  title     = {FunFact: Building Probabilistic Functional 3D Scene Graphs via Factor-Graph Reasoning},
  author    = {Fu, Zhengyu and Zurbr\"ugg, Ren\'e and Qu, Kaixian and Pollefeys, Marc and Hutter, Marco and
               Blum, Hermann and Bauer, Zuria},
  booktitle = {Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR)},
  month     = {June},
  year      = {2026}
}
```