GS4City: Hierarchical Semantic Gaussian Splatting via City-Model Priors

TL;DR

GS4City introduces a hierarchical semantic Gaussian Splatting method that leverages city-model priors for improved urban scene understanding, achieving superior semantic segmentation accuracy over existing methods.

Contribution

It integrates city model priors with Gaussian Splatting, explicitly recovering fine-grained facade details and establishing scene-consistent instance correspondences.

Findings

Outperforms existing 2D-driven semantic 3DGS methods by up to 15.8 IoU points.

Achieves 14.2 mIoU points improvement in fine-grained semantic segmentation.

Effectively incorporates structured building semantics into Gaussian scene representations.

Abstract

Recent semantic 3D Gaussian Splatting (3DGS) methods primarily rely on 2D foundation models, often yielding ambiguous boundaries and limited support for structured urban semantics. While city models such as CityGML encode hierarchically organized semantics together with building geometry, these labels cannot be directly mapped to Gaussian primitives. We present GS4City, a hierarchical semantic Gaussian Splatting method that incorporates city-model priors for urban scene understanding. GS4City derives reliable image-aligned masks from Level of Detail (LoD) 3 CityGML models via two-pass raycasting, explicitly using parent-child relations to validate and recover fine-grained facade elements. It then fuses these geometry-grounded masks with foundation-model predictions to establish scene-consistent instance correspondences, and learns a compact identity encoding for each Gaussian under joint 2D identity supervision and 3D spatial regularization. Experiments on the TUM2TWIN and Gold Coast datasets show that GS4City effectively incorporates structured building semantics into Gaussian scene representations, outperforming existing 2D-driven semantic 3DGS baselines, including LangSplat and Gaga, by up to 15.8 IoU points in coarse building segmentation and 14.2 mIoU points in fine-grained semantic segmentation. By bridging structured city models and photorealistic Gaussian scene representations, GS4City enables semantically queryable and structure-aware urban reconstruction. Code is available at https://github.com/Jinyzzz/GS4City.