Conference Agenda

This presentation introduces a digital twin and immersive VR system that reconstructs the “Hidden Foot” of Borobudur Temple in Central Java, Indonesia—an encased architectural layer containing 160 narrative bas-relief panels that cannot be directly observed today. The system integrates multi-source 3D point cloud data acquired via UAV and ground-level imaging with deep-learning–based 3D reconstructions of reliefs from historical monocular photographs and semantic segmentation results from previous work.

A custom passage model simulates the narrow gap between the original relief-bearing wall and the surrounding protective masonry, allowing users wearing a head-mounted display to virtually enter and walk through this otherwise inaccessible space. Within the VR environment, users can switch between photorealistic relief rendering and color-coded semantic overlays to support both immersive appreciation and analytical interpretation. A torch-based Level of Detail (LoD) strategy, driven by dynamic illumination, maintains high visual fidelity near the user while reducing rendering load for distant geometry, ensuring stable frame rates suitable for comfortable VR exploration.

A small user study indicates high ratings for visual realism, immersion, and the educational clarity of semantic overlays and gaze-triggered text annotations, highlighting the potential of this approach for research, documentation, and public engagement with hidden cultural heritage.

Three-dimensional (3D) scanning is widely used to preserve cultural heritage as large-scale point clouds. While these datasets contain rich geometric information, transparent visualization of such massive point clouds often suffers from visual clutter and reduced clarity, particularly when both external and internal structures are involved. Previous work resolved the problem of normal orientations, laying the foundation for robust shading in transparent visualization. Building on this foundation, this paper introduces a novel method of adaptive opacity control for region highlighting, which interprets shading as a distribution of opacity. By adjusting the lighting direction, effective opacity can be locally controlled without modifying the original point cloud data. This mechanism enables selective highlighting of user-specified regions, enhances the visibility of complex structures, while also allowing interactive dynamic shading by continuously changing the lighting direction. The effectiveness of the proposed method is demonstrated using culturally significant heritage point clouds, including UNESCO World Heritage sites, where intricate internal structures can be more clearly analyzed. Beyond cultural heritage, the proposed method is also applicable to modern architectural and other large-scale 3D scanned objects with similarly complex forms.

The concept of Digital Twin has attracted growing interest within research communities, including heritage conservation, in recent years. It combines detailed geometric documentation, real-time monitoring, and semantic information to create dynamic digital replicas of historic buildings. This paper presents the results of a scoping review of 204 peer-reviewed studies published between 2020 and 2025. The aim is to identify the main technologies, devices, and methods used to develop a Digital Twin for heritage buildings. The review reveals that terrestrial laser scanning (TLS), UAV photogrammetry, BIM, and IoT sensor networks form the core technological base. It also highlights the growing use of artificial intelligence for automated defect detection, predictive maintenance, and semantic processing. Based on the reviewed literature, the paper introduces a six-stage workflow for building a heritage Digital Twin, covering baseline documentation, static reality capture, semantic modelling, sensor integration, data fusion, and operational use. The findings show a clear shift from static 3D documentation toward dynamic, data-rich systems that support continuous monitoring and more informed decision-making. However, the review also identifies major challenges, including limited interoperability, complex data integration, incomplete AI validation, and long-term digital preservation issues. Overall, the study outlines the current state of Digital Twin technologies in architectural heritage and identifies key areas that require further research to support reliable and sustainable applications.

In the current context of energy and climate transition, the preventive conservation of historic buildings is particularly important due to their impact on architecture and works of art. Establishing the correlation between environmental variables and the condition of artworks in situ requires comprehensive and individualized monitoring, allowing for an understanding of cause-and-effect mechanisms. To address this challenge, the EPICO method provides a systematic framework for assessing deterioration risks in palace-museums through multi-scale monitoring and correlation between environmental parameters and object condition. The aim of the proposed topic is to enhance this decision-making tool with the creation of digital twins. These digital twins being fed with three-dimensional hyperspectral and LiDAR mapping of spaces and objects.

Urban digital twin systems require 3D city representations that reconcile semantic structure, geometric reliability, simulation capability, and photorealistic real-time rendering. Existing approaches typically prioritize a single modelling paradigm, limiting their capacity to simultaneously support analytical and visualization demands. CityGML ensures standardized semantics and topological consistency but often lacks detailed surface realism. Surface-based semantic mesh models preserve geometric detail suitable for environmental simulations but provide limited hierarchical semantic organization. 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 structured comparative framework linking LiDAR-derived CityGML, triangle-based semantic mesh, 3D Gaussian Splatting, and Triangle Splatting within a unified urban modelling workflow. UAV-based data acquired using a multirotor platform with 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 to provide a geometry-consistent baseline, 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. Rather than treating them as competing alternatives, the results reveal complementary modelling layers that can be systematically mapped. Based on these findings, the paper formulates a conceptual foundation for a unified 3D urban model capable of transforming consistently into semantic-structured, surface-based, and radiance-based representations, enabling adaptive and extensible urban digital twin systems.

Persistent Scatterer Interferometry (PSI) provides valuable information on ground and structural changes, particularly in dynamic urban environments. At the same time, urban digital twins (UDTs), as detailed three-dimensional representations of cities, are increasingly used for monitoring and analysis. However, the effective integration of results of PSI processing named Point Scatterers (PSs) into such frameworks remains challenging due to the limited positional accuracy of PSs, despite the high precision of displacement estimates. This study investigates a methodology for integrating PSI data from the European Ground Motion Service (EGMS) with airborne laser scanning (ALS) data and Level of Detail 2 (LoD2) building models to improve the connection of PSs with real-world objects. Three integration variants were analysed, differing in the reference datasets used for linking: (i) ALS point cloud, (ii) point cloud derived from LoD2 models and digital terrain model (DTM), and (iii) a combined approach integrating ALS and LoD2 representations. The results demonstrate that the combined approach yields the highest performance, achieving up to 88% of successfully linked PSs, compared to 70.4% and 80.3% for the ALS-only and LoD2-based approaches, respectively. The findings indicate that LoD2 models provide sufficient geometric detail for PS linking, despite lacking fine-scale building elements. Their use improves data completeness, particularly on building facades, where ALS data are often sparse or missing. The proposed methodology confirms the applicability of EGMS products as a valuable data source for 3D geoportals and urban digital twins, supporting advanced spatial analyses in complex environments.

Integrated Water Service (IWS), which combines water supply and wastewater treatment, requires complex geometric and semantic management. Building Information Modelling (BIM) and Geographic Information Systems (GIS) are the two main geospatial technologies involved in this field. In very simple terms, BIM allows to have 3D models with detailed geometric and semantic information, and GIS permits to geolocate and manage the models in the territory. To facilitate the integration of these two systems, we propose to manage the BIM models through a standardised relational database. In the BIM world, relational databases are not yet widely used, but the technology is already available. For example, ifcSQL is an encoding of the Industry Foundation Classes (IFC) data model for a relational database. This article proposes an extension of the ifcSQL database with the added possibility to store the georeferenced explicit geometries of the IFC models. Additionally, we present a prototype to make such IFC-based data available via QGIS. In this way, a user can interact with BIM data using open GIS technologies. As a result, it is possible to visualise the models in 2D and 3D, and to perform queries on their attributes. A set of real-world case studies has served as testing ground to develop the functionalities that allow for the interaction with the BIM models via QGIS. Such test cases originate from interviews with a company that manages IWS in Northeast Italy.