Occupancy-Grounded Room Segmentation for Hierarchical 3D Scene Graphs

2026-06-11

AI Summary

This work addresses the lack of a consistent geometric evaluation criterion for room nodes in existing hierarchical 3D scene graphs, which leads to structural inconsistencies. To resolve this, the authors propose a novel approach grounded in occupancy decomposition that tracks free-space regions and generates polygonal footprints, thereby introducing free space as the first geometric anchor for room nodes. This strategy unifies both the construction and evaluation of the room layer. By integrating occupancy decomposition, free-space tracking, polygon generation, and matching with Matterport3D room instances, the method significantly improves room recall across twelve scenes. Although precision experiences a slight decline, the results highlight wall alignment boundaries as a persistent challenge across diverse environments.

Abstract

Hierarchical 3D scene graphs (3DSGs) for indoor robots organize geometric and semantic information across spatial scales, with a room layer that connects object-level perception to room-scale reasoning. Existing systems construct this layer from different spatial substrates (\eg{} place clusters, wall planes, or segmentation outputs), and as a result, room nodes are not evaluated on a common geometric criterion. We present an occupancy-grounded 3DSG pipeline in which room nodes are anchored to tracked free-space regions derived from occupancy decomposition, giving each room an explicit polygonal footprint. We evaluate the pipeline on 12 Matterport3D scenes by matching predicted room polygons to annotated room instances and compare against Hydra, a representative state-of-the-art place-connectivity baseline. The results show that occupancy-grounded anchoring recovers substantially more room instances than place-connectivity construction, at the cost of lower precision, and that wall-accurate room boundaries remain an open problem for both methods. Code is available at https://github.com/crcz25/OccuSG.

Problem

• Hierarchical 3D scene graphs
• room segmentation
• occupancy decomposition
• room instance recovery
• geometric consistency

Innovation

• occupancy decomposition
• room segmentation
• 3D scene graphs
• free-space tracking
• polygonal room footprint