Research - Extended Reality and Interaction

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  Harvesting Natural Points-of-View Preferences for Arbitrary Objects

  G. Roveda, G. Papaioannou, A. A. Vasilakis, M. Tarini, Eurographics Workshop on 3D Object Retrieval, short paper, 2026.

  Abstract. Automatically identification of an optimal, representative or relevant viewpoint for a given 3D object is an important task with several applications in digital marketing, visualization, 3D data management and shape retrieval. An objective function to optimize the viewpoint is difficult to define in purely geometric terms, given the semantic and aesthetic bias a user is likely to introduce when presented with a target object. Therefore, supervised data-driven approaches are a natural candidate to address the problem. This implies the availability of large datasets describing natural point-of-view preferences for a number of object categories. In this work, we present a framework designed to harvest this kind a dataset. The system involves tasking end-users with answering general qualitative questions about a displayed 3D object, while silently collecting point-of-view information. In other terms, we capture viewpoint preferences as a latent objective, allowing for an unbiased observation of user behavior in performing various tasks that involve object visualization. We publicly release both our dataset of collected viewpoint statistics and the tool to harvest them, which is easily configurable by experimenters to collect more data in the future or integrate the approach into online 3D viewers.

  Downloads: author-prepared version of the poster paper

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  HOPE: Holographic Optimized Processing Engine

  V. E. Kotsis-Panakakis, I. Evangelou, F. Bistas, A. Gkaravelis, N. Vitsas, A. A. Vasilakis, G. Papaioannou, EuroXR 2025, poster session, 2025.

  Abstract. In this work we introduce a context-aware system designed to enable efficient, scalable holographic communication. HOPE uses gesture recognition & semantic-aware filtering to prioritize key details, improving interactivity and realism. Smart mesh compression and adaptive tuning allow responsive performance. The real-time producer-consumer pipeline for holographic streaming processes a point cloud produced by one or more 3D cameras, performing hand tracking, point cloud segmentation and importance computation, background removal and point cloud compression. A core innovation in HOPE is its context-aware processing: instead of treating all data equally, it selectively prioritizes important visual regions, while suppressing redundant or low-value information. The resulting data stream is efficiently encoded, transmitted in real time, decoded and visualized on the client's XR device.

  Downloads: author-prepared version of the poster paper     the poster

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  The Impact of Normal Mapping on the Geometric Simplification of Archaeological 3D Data

  S. Costopoulos, G. Papaioannou, Proc. 52nd Int. Conf. Computer Applications and Quantitative Methods in Archaeology (CAA), 2025.

  Abstract. A great challenge in 3D digitization and modelling lies in striking a balance between surface detail and model size. Large models severely impact storage requirements, data transmission and 3D rendering. It is therefore typical for high-resolution digitized objects and modelled assets alike to produce sub-sampled and simplified versions to match the requirements of the intended applications. By doing so however, geometric detail is lost, affecting visual fidelity during 3D visualization. An established computer graphics method for the preservation of visual fidelity of low-detail versions is normal mapping, i.e. the estimation and transfer of the local surface orientation variation of the high-resolution mesh onto a texture image. The “baked” local surface detail is then applied during rendering to the low-resolution version, simulating details via the illumination computation. In this work, we explore the robustness of detail transfer via normal mapping on decimated 3D digitized archaeological objects and sites, by evaluating the technique with a diverse set of test cases and user groups of different familiarity to 3D content and expertise. The results have successfully demonstrated that low-resolution models with normal maps can effectively stand in for the high-resolution ones for many data visualization applications. .

  Downloads: extended abstract     Peer Community Journal article

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  Spatiotemporal Reconstruction of Pot Burial Excavations

  M. Grigoriadi, G. Papaioannou, Proc. 52nd Int. Conf. Computer Applications and Quantitative Methods in Archaeology (CAA), 2025.

  Abstract. This study focuses on the small-scale excavation case of pot-burials, a process which given the dimensions and the fragility of ceramic vessels and its contents, makes thorough documentation essential for post-excavation analysis and interpretation. The main goal was to establish a reliable complementary approach to typical documentation and recording of a pot-burial excavation, by integrating the temporal as well as the fully spatial dimensions of the excavated object. Key objectives included the development of an interactive time-lapse of the excavation utilizing Structure-from-Motion (SfM) photogrammetry and an established interactive 3D visualization solution, while assessing the methodology’s practicality for documentation, labor investment, and educational potential. The findings could significantly benefit both archaeological research and public engagement. .

  Downloads: author-prepared version of the paper

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  Real-Time Volume Editing on Low-Power Virtual Reality Devices

  I. Evangelou, A. Gkaravelis, G. Papaioannou, Proc. 18th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (GRAPP), 2023.

  Abstract. The advent of consumer-grade, low-power, untethered virtual reality devices has spurred the creation of numerous applications, with important implications to training, socialisation, education and entertainment. However, such devices are typically based on modified mobile architectures and processing units, offering limited capabilities in terms of geometry and shading throughput, compared to their desktop counterparts. In this work we provide insights on how to implement two combined and particularly challenging tasks on such a platform, those of real-time volume editing and physically-based rendering. We implement and showcase our techniques in the context of a virtual sculpting edutainment application, intended for mass deployment at a virtual reality exhibition centre.

  Downloads: author-prepared version of the paper

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  First-person Interactive Experience of a Concentration Camp: The Case of Block 15

  A. Benardou, A. M. Droumpouki, G. Papaioannou, Difficult Heritage and Immersive Experiences (A. Benardou, A. M. Droumpouki - Eds.), ISBN 9781032060866, Routledge, pp. 145 - 160, 2022.

  Abstract. This paper focuses on the infamous Block 15 of the Haidari Concentration Camp in Western Athens, the largest and most notorious German concentration camp in wartime Greece, as a showcase of a largely neglected site of difficult heritage and will attempt to make the building, currently an endangered one, accessible to audiences and communities of diverse backgrounds through the use of immersive technologies. Through an original scenario based on primary and multimedia archival sources that are largely based on digital storytelling, this interactive, immersive Virtual Reality experience does not only bring back to life the actual monument that is Block 15, but also functions as a reminder of the horrors and torture inflicted by the Nazis on prisoners, in an attempt to educate and to reintroduce a historically and politically contested site to heterogeneous audiences, both in situ as well as in sites outside the concentration camp.

  Downloads: author-prepared version of the chapter

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  Tile-based Caching Optimization for 360° Videos

  G. Papaioannou, I. Koutsopoulos, Proc. ACM International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc),2019.

  Abstract. Panoramic or 360° video streaming and playback offer an immersive viewing experience and become increasingly popular, albeit very resource-demanding. Caching of 360° video content close to the user reduces content delivery delay and bandwidth consumption. Contrary to monolithic singlestream transmission, the recently proposed tiling approach allows the streaming of different parts (tiles) of the 360° content with different resolutions. We study the problem of optimal caching of 360° video streams, where the problem is to decide which tiles and tile resolutions to cache. The difference from conventional video is that each tile may need to be cached with multiple resolutions since it may appear in different positions in different viewports, and the proportions of these positions are dictated by viewing statistics through e.g. Head-Mounted Display units. This observation leads to a novel caching objective: the cached resolutions for each tile should be as close as possible to the required ones for each tile when viewed by the user.

  We study the cases of caching tile streams either at different resolutions or in a layered encoding fashion. We seek to optimize an objective that combines (i) an error metric between requested and cached tile resolutions across different viewports, and (ii) coverage of the tile set. For the case of multiple resolutions, we show that the problem of selection of tile resolutions to cache so as to minimize the error metric above is equivalent to the K-Medoids problem. For layered encoding, the problem is to find the maximumresolution layer to cache for each tile stream, and we show that this is equivalent to a Multiple-Choice Knapsack problem. We present an implementation of the cache optimization scheme, evaluate our model on a tiled 360° video distribution simulator and demonstrate a significant increase in cache hit ratio over state-of-the-art caching strategies.

  Downloads: author-prepared version of the paper

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  An Automated Modeling Method for Multiple Detail Levels of Real-time Trees

  C. Koniaris, A. Gaitatzes, G. Papaioannou, Proc. IEEE Int. conf. Games and Virtual Worlds for Serious Applications, pp.53-60, 2009.

  Abstract. Rendering realistic outdoor scenes in realtime applications is a difficult task to accomplish since the geometric complexity of the objects, and most notably of trees, is too high for current hardware to handle efficiently in large amounts. Our method generates trees with self-similarity, and later exploits this property by heavily sharing prerendered textures of similar parts of the tree. The intrinsic tree hierarchy of the trees, combined with their self-similarity, allows generation of multiple levels of detail. Here we present the flow of the processing stage, from the collection of the required input data until the export of the models in all their levels of detail as well as related and additional data.

  Downloads: the paper

  Reference: BibTex  

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  Designing a Real-time Playback System for a Dome Theater

  D. Christopoulos, A. Gaitatzes, G. Papaioannou, G. Zyba, Proc. Eurographics 7th International Symposium on Virtual Reality, Archaeology and Intelligent Cultural Heritage (VAST), pp. 35-40, 2006.

  Abstract. Designing a Real-time Playback System for a Dome TheaterMost dome display systems today employ pre-rendered shows for attracting visitors. In addition since the technology is well established, developers have many tools at their disposal for creating such shows. On the contrary real-time shows for dome displays are just starting to appear. As a result the production of such shows is not a standardized process. Slowly, progress is made. Graphics generator cards are able to support the required SXGA+ resolutions and the supporting cluster systems are able to supply the processing power and memory bandwidth that such real-time systems require. Tools have to be developed and new processes have to be established. The Foundation of the Hellenic World (FHW) having produced numerous real-time productions for immersive flat display systems has great experience in realizing such shows. In this paper we present the technological developments for the production of real time applications for digital dome display systems.

  Downloads: the paper

  Reference: BibTex  

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  Efficient Occlusion Culling using Solid Occluders

  G. Papaioannou, A. Gaitatzes, D. Christopoulos, Proc. 14th International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision (WSCG '2006), pp. 85-93, 2006.

  Abstract. Occlusion culling is a genre of algorithms for rapidly eliminating portions of three-dimensional geometry hidden behind other, visible objects prior to passing them to the rendering pipeline. In this paper, an extension to the popular shadow frustum culling algorithm is presented, which takes into account the fact that many planar occluders can be grouped into compound convex solids, which in turn can provide fewer and larger culling frusta and therefore more efficient elimination of hidden geometry. The proposed method combines planar and solid occluders using a unified selection approach and has been tested on a commercially deployed virtual reality system.

  Downloads: the paper    color figure 1   color figure 2

  Reference: BibTex  

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  Media Productions for a Dome Display System

  A. Gaitatzes, G. Papaioannou, D. Christopoulos, G. Zyba, Proc. ACM Symposium on Virtual Reality Software and Technology (VRST) 2006, pp. 261-264, 2006.

  Abstract. As the interest of the public for new forms of media grows, museums and theme parks select real time Virtual Reality productions as their presentation medium. Based on three-dimensional graphics, interaction, sound, music and intense story telling they mesmerize their audiences. The Foundation of the Hellenic World (FHW) having opened so far to the public three different Virtual Reality theaters, is in the process of building a new Dome-shaped Virtual Reality theatre with a capacity of 130 people. This fully interactive theatre will present new experiences in immersion to the visitors. In this paper we present the challenges encountered in developing productions for such a large spherical display system as well as building the underlying real-time display and support systems.

  Downloads: the paper

  Reference: BibTex  

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  The Ancient Olympic Games: Being Part of the Experience

  A. Gaitatzes, D. Christopoulos and G. Papaioannou , proc. 5th Eurographics International Symposium on Virtual Reality, Archaeology and Cultural Heritage VAST (2004)

  Abstract. This paper presents the virtual reality applications that the Foundation of the Hellenic World has produced associated with the Olympic Games in ancient Greece. The separate virtual reality shows are presented in terms of interactivity and educational value. The technical aspects of the productions are next explained in detail, with an emphasis on character animation, dynamics and occlusion culling for surround screen projection environments. These techniques were mostly utilised in the recent production regarding the ancient pentathlon, where much effort has been made to recreate the feeling of the games and help the user/spectator be an interacting part of the edutainment activity.

  Downloads: the paper

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  Enhancing Virtual Walkthroughs of Archaeological Sites

  G. Papaioannou, A. Gaitatzes, D. Christopoulos, proc. Eurographics 4th International Symposium on Virtual Reality, Archaeology and Intelligent Cultural Heritage (VAST), pp. 175-184, 2003.

  Abstract. This paper describes the methodological aspects of the application of various established and new graphics techniques in virtual reality applications, in order to visually enrich conventional walkthroughs and extend the common capabilities of virtual environment visualization platforms. The paper describes these techniques and goes to the extent of explaining various practical implementation issues. Examples and application case studies are provided to demonstrate the enhancements.

  Downloads: the paper

  Reference: BibTex  

Contact info: Georgios Papaioannou, gepap @ aueb gr