Abstract. 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.
Hatsuki Nojiri, Satoshi Takatori, Liang Li et al.· ISPRS Annals of the Photogra...· 0 citations
Abstract. While virtual reality (VR) has been increasingly adopted for the digital archiving of cultural heritage, most existing systems focus on visual appreciation rather than structural analysis. To address this limitation, this study proposes a transparent VR visualization system designed to enhance the recognition of structural features in 3D scanned point clouds of historic architecture. Using a large-scale point cloud dataset of the main hall of Tamaki Shrine, which is part of the UNESCO World Heritage site “Sacred Sites and Pilgrimage Routes in the Kii Mountain Range,” the data were initially processed using Poisson disk sampling to optimize real-time rendering throughput while preserving geometric fidelity. Structural salience was subsequently quantified through principal component analysis (PCA), employing linearity for sharp-edge extraction and the change of curvature for soft-edge representation. To alleviate the occlusion inherent in opaque point cloud rendering, we implemented a custom alpha-blending shader in Unity. This enabled two types of transparent feature-enhanced visualization: binarization for highlighting sharp edges and opacity gradation for visualizing soft-edge regions. The developed system, operated with a Meta Quest Pro, provides distinct viewing and analysis modes. Experimental results demonstrate that combining feature enhancement with opacity control improves the visibility of internal depth relationships and point-density variations in complex wooden architecture, thereby supporting structural understanding that is difficult to achieve with conventional rendering.
Taishi Matsuo, Satoshi Takatori, Liang Li et al.· The International Archives o...· 0 citations
Abstract. The Borobudur Temple’s Hidden Foot (Karmawibhangga layer), comprising 160 bas-relief panels sealed behind protective stone cladding since the early 20th century, presents a compelling challenge for digital cultural heritage practice. This paper presents a digital twin reconstruction and immersive virtual reality (VR) system that provides interactive access to this physically inaccessible archaeological space. The system integrates three pre-existing datasets: UAV photogrammetric point clouds of the outer temple structure, deep-learning-based 3D relief reconstructions derived from archival photographs (Pan et al., 2022), and semantic segmentation results of relief surfaces (Ji et al., 2023). Within a Unity 2022.3.22f1-based VR environment optimised for the HTC VIVE Pro Eye head-mounted display, these datasets are unified into a navigable Hidden Foot passage. A novel lighting-driven Level of Detail (LoD) strategy—where rendering complexity is governed by the illumination radius of a virtual torch—achieves 65–70 FPS on the HMD while preserving visual fidelity within the illuminated zone. Eye-gaze-triggered textual annotations support contextual iconographic interpretation, while interactive toggling between photorealistic and semantically labelled views enables both casual exploration and scholarly analysis. A user study (n = 10) employing a System Usability Scale-adapted questionnaire yielded mean satisfaction ratings exceeding 4.5/5 across all evaluation dimensions. The system demonstrates a scalable methodology for transforming inaccessible heritage layers into immersive, annotated digital environments.
Satoshi Takatori, Jiajun Gao, Liang Li et al.· The International Archives o...· 0 citations
An adaptive neighborhood scale selection method for local PCA, designed for robust edge extraction from large-scale 3D scanned point clouds, and the use of octree-based spatial indexing ensures computational efficiency, making the method practical for field-based heritage conservation and structural analysis on consumer-grade hardware.
Tomoya Okajima, Satoshi Takatori, F. I. Thufail et al.· The International Archives o...· 0 citations