Abstract. Urban digital twins increasingly require pedestrian-scale three-dimensional (3D) representations to support accessibility and inclusiveness assessment. However, existing approaches typically emphasize either geometric accuracy or visual realism, while lacking an integrated framework for analysing pedestrian-level conditions. This study proposes a hybrid workflow integrating handheld LiDAR and 3D Gaussian Splatting (3DGS) within a CityGML-based semantic framework for accessibility assessment. Handheld LiDAR provides centimetre-level geometric measurements, enabling the extraction of key indicators such as slope, surface roughness, and obstacle presence. In parallel, 3DGS reconstruction from 360° video imagery enhances visual realism and perceptual understanding. Both datasets are co-registered and structured within the CityGML 3.0 Transportation model to represent pedestrian environments in a unified spatial and semantic framework. Accessibility assessment was conducted using three approaches: LiDAR-based analysis, field survey observations, and immersive evaluation in a Virtual Reality (VR) environment. The LiDAR-based results were used as reference. Comparative analysis shows that field survey assessment achieves an agreement of approximately 85.7%, while VR-based assessment reaches approximately 75.4%. The results indicate that while VR does not replace metric-based analysis, it enables perception-driven and participatory evaluation. In particular, VR-based assessment shows potential to involve users, including people with disabilities, in accessibility evaluation through immersive and remote interaction. The proposed approach contributes to the development of human-scale urban digital twins by integrating metric accuracy, semantic structure, and participatory evaluation for more inclusive accessibility analysis.
D. Suwardhi, Wahyunan Andika, R. Widyastuti et al.· The International Archives o...· 0 citations
Abstract. Urban digital twin systems require 3D city representations that reconcile semantic structure, geometric reliability, simulation capability, and photorealistic real-time rendering. Existing approaches usually prioritize a single modelling paradigm, limiting their ability to support both analytical and visualization needs. CityGML provides standardized semantics and topology but often lacks surface realism. Semantic mesh models preserve geometric detail suitable for environmental simulations but provide limited hierarchical semantics. In contrast, neural radiance-field approaches such as 3D Gaussian Splatting (3DGS) enable photorealistic rendering at interactive frame rates but do not explicitly encode topology or structured semantics. This study establishes a comparative framework linking LiDAR-derived CityGML, semantic mesh, 3D Gaussian Splatting, and Triangle Splatting within a unified urban modelling workflow. UAV data acquired using a DJI ZENMUSE L2 sensor serve as the geometric backbone for reconstructing CityGML LoD1–LoD2 models. The semantic model is transformed into a textured triangular mesh, while radiance-based models are generated from the same imagery using multiple 3DGS implementations and a triangle splatting framework. Comparative evaluation investigates geometric coherence, semantic preservation, and radiance consistency to identify structural correspondences across the representations. The results reveal complementary modelling layers that can be systematically mapped rather than treated as competing alternatives. Based on these findings, the paper proposes a conceptual foundation for a unified 3D urban model capable of transforming consistently into semantic, surface-based, and radiance-based representations for adaptive urban digital twin systems. Data are freely accessible for research purposes at https://github.com/3DOM-FBK/urban-representation-fusion/.
D. Suwardhi, Muhammad Arif Sudibyo, Agus Ambarwari et al.· The International Archives o...· 0 citations
Abstract. Hybrid airborne imaging systems integrating oblique photogrammetric cameras and LiDAR sensors provide complementary geometric and radiometric information for high-fidelity 3D reconstruction. While LiDAR offers stable global geometric accuracy, photogrammetric reconstructions provide dense surface detail and rich fac¸ade information through oblique imaging. However, photogrammetric models often exhibit locally varying geometric drift caused by error accumulation during bundle adjustment, preventing pixel-accurate alignment between images and LiDAR data. Conventional global registration approaches are insufficient to correct such spatially varying misalignments. In this paper, we propose a view-dependent fusion framework for pixel-accurate registration between photogrammetric images and LiDAR data. The global alignment problem is decomposed into localized rigid registrations performed independently for each image. For each view, a local photogrammetric point cloud reconstructed from depth maps is rigidly aligned to a corresponding LiDAR subset using fixed-scale point-to-plane ICP. The estimated transformation is used to project LiDAR points into the image domain, where depth-consistency checks enforce visibility constraints and remove inconsistent measurements. Valid LiDAR points are colorized and fused with the photogrammetric reconstruction to generate anchored view-dependent point clouds. Finally, all view-dependent reconstructions are aggregated using voxel-grid fusion with medianbased point selection. Experiments on airborne oblique imaging datasets demonstrate improved reconstruction completeness and pixel-level consistency between images and LiDAR geometry. The proposed framework provides a practical and robust solution for high-accuracy multi-modal 3D reconstruction in complex urban environments.
Deyan Deng, Rongjun Qin, E. M. Farella et al.· The International Archives o...· 0 citations
Abstract. The 3D reconstruction of cultural heritage artefacts plays a crucial role in documentation, conservation and dissemination. While recent advances in photogrammetry, laser scanning and neural rendering techniques have significantly improved the geometric accuracy and visual realism of digitised assets, the reconstruction of transparent and reflective materials - typical in museal collections - remains a major challenge. Materials such as glass, glazes and varnishes exhibit complex optical behaviours, leading to incomplete or inaccurate 3D models. Recent developments in Gaussian Splatting (GS) offer a potential alternative by enabling efficient, high-fidelity scene representation without explicit surface modelling. However, their application to non-Lambertian and transparent heritage objects remains largely unexplored. This paper presents a study on GS methods for the 3D digitisation of transparent cultural heritage artefacts. Through a series of experimental reconstructions, the work investigates the potential and limitations of GS, highlight the opportunities of hybrid pipelines for addressing long-standing challenges in the digitisation of non-collaborative materials.
Marco Medici, Andrea Sterpin, Stefano Settimo et al.· The International Archives o...· 0 citations
Abstract. This paper introduces the 3D-4CH project and its open framework, i.e. a sustainable ecosystem of tools designed to overcome the fragmentation and limited maintainability of previous EU-funded 3D heritage initiatives. Aligned with the European Collaborative Cloud for Cultural Heritage (ECCCH), the framework integrates an end-to-end pipeline for 3D data generation and processing, semantic enrichment and long-term dissemination, including metadata and paradata inclusion. The 3D-4CH initiative bridges the gap between ICT research and operational heritage practices, ensuring the scalability and reproducibility of 3D digital assets for crossinstitutional data sharing and preservation. All software components, including GitHub repositories and online processing frameworks, are openly available, in accordance with open science principles and FAIR data practices. Further information is available at https://www.3d4ch-competencecentre.eu/en/tools/.
F. Arnaoutoglou, P. Bonsma, E. M. Farella et al.· The International Archives o...· 0 citations
This work proposes a hybrid reconstruction pipeline, leveraging the strengths and benefits of each technique, which exploits the accurate geometry of photogrammetry in well-textured regions and the GS capabilities to improve completeness and visual aspect in areas featuring non-collaborative surfaces.
Fabio Remondino, E. M. Farella, Gianluca Bertolasi et al.· The International Archives o...· 0 citations
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