VSG-GS: UAV Oblique Imagery for Semantic-Guided 3D Gaussian Splatting Bridge Reconstruction

Ground sampling distance (GSD) is approximately 2.0–3.5 cm/pixel.Caiyuanba Bridge (N 29°31′–29°33′, E 106°32′–106°34′), located in Yuzhong District, Chongqing, China. This is a steel-tied arch bridge crossing the Yangtze River in a dense urban setting. Data were collected in March 2025.

The flight was conducted at 100–150 m altitude with multi-angle oblique photography, producing 892 images at 5,280 × 3,956 px resolution. GSD is approximately 2.5–4.0 cm/pixel.All images were captured in JPEG format. Invalid images (severe motion blur, exposure anomalies, or excessive redundancy) were manually removed during post-screening.2.

Tools and SoftwareCOLMAP (v3.9.1): Structure-from-Motion for camera pose recovery and sparse point cloud initialization.Florence-2 (Microsoft, pretrained): Zero-shot box-level bridge localization using the text prompt "The most prominent bridge in the scene."SAM2 (Meta, fine-tuned as Bridge-SAM2): Promptable segmentation for pixel-level bridge mask generation. The fine-tuning was performed on a manually annotated subset (~200 images per dataset) with iterative hard-sample refinement over 3 rounds.3D Gaussian Splatting (base implementation by Kerbl et al., 2023): Modified with mask-constrained loss and adaptive density control restricted to bridge ROI.Hardware: Training was conducted on an NVIDIA RTX 4090 GPU (24 GB VRAM) with an AMD Epyc 7542 CPU and 512 GB RAM.