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Item Challenges in the Digitisation of a High-reflective Artwork(The Eurographics Association, 2021) Catalano, Chiara Eva; Brunetto, Erika; Mortara, Michela; Pizzi, Corrado; Hulusic, Vedad and Chalmers, AlanIn this paper we report about the photogrammetric acquisition and reconstruction of a contemporary artwork, performed by offthe- shelf software. The ceramic piece of art is "Il Libro d'Oro del Terzo Paradiso" ("The Golden Book of the Third Paradise") by Michelangelo Pistoletto, accessed and studied in the framework of a regional project. This artefact is particularly challenging. On the one hand, it is golden coated and, as such, highly reflective. Hence, images are likely to suffer from highlight spots, shadows or self-reflections, and the reconstructed point cloud is typically noisy. On the other hand, the object exhibits simple geometry, mainly composed of planar surfaces, and is highly symmetric; however, it possesses detail features and undercuts. The symmetric nature of the object and reflections misled the image alignment, and the noise in the data turned out to be of the same scale as the detail features. We will discuss all the steps of the process, aimed at obtaining a high quality and accurate 3D model using low-cost tools.Item Quad Layouts via Constrained T-Mesh Quantization(The Eurographics Association and John Wiley & Sons Ltd., 2021) Lyon, Max; Campen, Marcel; Kobbelt, Leif; Mitra, Niloy and Viola, IvanWe present a robust and fast method for the creation of conforming quad layouts on surfaces. Our algorithm is based on the quantization of a T-mesh, i.e. an assignment of integer lengths to the sides of a non-conforming rectangular partition of the surface. This representation has the benefit of being able to encode an infinite number of layout connectivity options in a finite manner, which guarantees that a valid layout can always be found. We carefully construct the T-mesh from a given seamless parametrization such that the algorithm can provide guarantees on the results' quality. In particular, the user can specify a bound on the angular deviation of layout edges from prescribed directions. We solve an integer linear program (ILP) to find a coarse quad layout adhering to that maximal deviation. Our algorithm is guaranteed to yield a conforming quad layout free of T-junctions together with bounded angle distortion. Our results show that the presented method is fast, reliable, and achieves high quality layouts.Item Stable and Efficient Differential Estimators on Oriented Point Clouds(The Eurographics Association and John Wiley & Sons Ltd., 2021) Lejemble, Thibault; Coeurjolly, David; Barthe, Loïc; Mellado, Nicolas; Digne, Julie and Crane, KeenanPoint clouds are now ubiquitous in computer graphics and computer vision. Differential properties of the point-sampled surface, such as principal curvatures, are important to estimate in order to locally characterize the scanned shape. To approximate the surface from unstructured points equipped with normal vectors, we rely on the Algebraic Point Set Surfaces (APSS) [GG07] for which we provide convergence and stability proofs for the mean curvature estimator. Using an integral invariant viewpoint, this first contribution links the algebraic sphere regression involved in the APSS algorithm to several surface derivatives of different orders. As a second contribution, we propose an analytic method to compute the shape operator and its principal curvatures from the fitted algebraic sphere. We compare our method to the state-of-the-art with several convergence and robustness tests performed on a synthetic sampled surface. Experiments show that our curvature estimations are more accurate and stable while being faster to compute compared to previous methods. Our differential estimators are easy to implement with little memory footprint and only require a unique range neighbors query per estimation. Its highly parallelizable nature makes it appropriate for processing large acquired data, as we show in several real-world experiments.Item Virtual Dance Museum: the Case of Greek/Cypriot Folk Dancing(The Eurographics Association, 2021) Aristidou, Andreas; Andreou, Nefeli; Charalambous, Loukas; Yiannakidis, Anastasios; Chrysanthou, Yiorgos; Hulusic, Vedad and Chalmers, AlanIn this paper, we have designed and developed a virtual dance museum to provide the technological tools that allow for widely educating the public, most specifically the youngest generations, about the story, costumes, music, and history of our dances. The holistic documentation of our intangible cultural heritage creations is a critical necessity for the preservation and the continuity of our identity as Europeans. In that direction, we have employed a specially designed relational database schema that holistically structures the information within the database, and is ideal for archiving, presenting, further analyzing, and re-using dance motion data. Data have been retargeted to a virtual character, dressed with traditional uniform and simulated to achieve realism. The users can view and interact with the archived data using advanced 3D character visualization in three ways: via an online 3D virtual environment; in virtual reality using headset; and in augmented reality, where the 3D characters can co-inhabit the real world. Our museum is publicly accessible, and also enables motion data reusability, facilitating dance learning applications through gamification.Item Collision Free Simplification for 2D Multi-Layered Shapes(The Eurographics Association, 2023) Gong, Xianjin; Parakkat, Amal Dev; Rohmer, Damien; Pelechano, Nuria; Liarokapis, Fotis; Rohmer, Damien; Asadipour, AliWe propose a simplification-aware untangling algorithm for 2D layered shapes stacked on each other. While the shape undergoes simplification, our approach adjusts the vertex positions to prevent collision with other layers while simultaneously maintaining the correct relative ordering and offsets between the layers. The method features a field-based representation of the shapes and extends the concept of "implicit untangling" by incorporating interleaved shape preservation through a parameterized shape-matching technique. Our approach can be plugged on top of any existing vertex-decimation approach, leveraging its localized nature to accelerate the field evaluation. Furthermore, our method can seamlessly handle an arbitrary number of stacked layers, making it a versatile solution for stacked garment simplification.Item Sketching Vocabulary for Crowd Motion(The Eurographics Association and John Wiley & Sons Ltd., 2022) Mathew, C. D. Tharindu; Benes, Bedrich; Aliaga, Daniel; Dominik L. Michels; Soeren PirkThis paper proposes and evaluates a sketching language to author crowd motion. It focuses on the path, speed, thickness, and density parameters of crowd motion. A sketch-based vocabulary is proposed for each parameter and evaluated in a user study against complex crowd scenes. A sketch recognition pipeline converts the sketches into a crowd simulation. The user study results show that 1) participants at various skill levels and can draw accurate crowd motion through sketching, 2) certain sketch styles lead to a more accurate representation of crowd parameters, and 3) sketching allows to produce complex crowd motions in a few seconds. The results show that some styles although accurate actually are less preferred over less accurate ones.Item Recreational Motion Simulation: A New Frontier for Virtual Worlds Research(The Eurographics Association, 2021) Williams, Benjamin; Headleand, Christopher J.; Xu, Kai and Turner, MartinMotion simulation is a developing field which continues to grow with the recent incline in commercial virtual reality. Whilst the majority of motion simulation research focuses on flight simulation and training, its utility in recreational settings is often overlooked. Despite this lack of research, the use of motion simulators for recreational purposes spans decades, and is still today one of the most popular applications of motion simulator devices. Furthermore, with the recent development of low-cost motion simulation platforms, consumers have begun to use these devices in the home. Research regarding motion simulation and its effects in recreational experiences is needed now more than ever, and in this position paper we outline several reasons for its importance.Item User-centred Depth Estimation Benchmarking for VR Content Creation from Single Images(The Eurographics Association, 2021) Dickson, Anthony; Knott, Alistair; Zollmann, Stefanie; Lee, Sung-Hee and Zollmann, Stefanie and Okabe, Makoto and Wünsche, BurkhardThe capture and creation of 3D content from a device equipped with just a single RGB camera has a wide range of applications ranging from 3D photographs and panoramas to 3D video. Many of these methods rely on depth estimation models to provide the necessary 3D data, mainly neural network models. However, the metrics used to evaluate these models can be difficult to interpret and to relate to the quality of 3D/VR content derived from these models. In this work, we explore the relationship between the widely used depth estimation metrics, image similarly metrics applied to synthesised novel viewpoints, and user perception of quality and similarity on these novel viewpoints. Our results indicate that the standard metrics are indeed a good indicator of 3D quality, and that they correlate with human judgements and other metrics that are designed to follow human judgements.Item Next Event Estimation++: Visibility Mapping for Efficient Light Transport Simulation(The Eurographics Association and John Wiley & Sons Ltd., 2020) Guo, Jerry Jinfeng; Eisemann, Martin; Eisemann, Elmar; Eisemann, Elmar and Jacobson, Alec and Zhang, Fang-LueMonte-Carlo rendering requires determining the visibility between scene points as the most common and compute intense operation to establish paths between camera and light source. Unfortunately, many tests reveal occlusions and the corresponding paths do not contribute to the final image. In this work, we present next event estimation++ (NEE++): a visibility mapping technique to perform visibility tests in a more informed way by caching voxel to voxel visibility probabilities. We show two scenarios: Russian roulette style rejection of visibility tests and direct importance sampling of the visibility. We show applications to next event estimation and light sampling in a uni-directional path tracer, and light-subpath sampling in Bi-Directional Path Tracing. The technique is simple to implement, easy to add to existing rendering systems, and comes at almost no cost, as the required information can be directly extracted from the rendering process itself. It discards up to 80% of visibility tests on average, while reducing variance by ~20% compared to other state-of-the-art light sampling techniques with the same number of samples. It gracefully handles complex scenes with efficiency similar to Metropolis light transport techniques but with a more uniform convergence.Item An Approach to the Decomposition of Solids with Voids via Morse Theory(The Eurographics Association, 2023) Pareja-Corcho, Juan; Montoya-Zapata, Diego; Moreno, Aitor; Cadavid, Carlos; Posada, Jorge; Arenas-Tobon, Ketzare; Ruiz-Salguero, Oscar; Banterle, Francesco; Caggianese, Giuseppe; Capece, Nicola; Erra, Ugo; Lupinetti, Katia; Manfredi, GildaThe decomposition of solids is a problem of interest in areas of engineering such as feature recognition or manufacturing planning. The problem can be stated as finding a set of smaller and simpler pieces that glued together amount to the initial solid. This decomposition can be guided by geometrical or topological criteria and be applied to either surfaces or solids (embedded manifolds). Most topological decompositions rely on Morse theory to identify changes in the topology of a manifold. A Morse function f is defined on the manifold and the manifold's topology is studied by studying the behaviour of the critical points of f . A popular structure used to encode this behaviour is the Reeb graph. Reeb graph-based decompositions have proven to work well for surfaces and for solids without inner voids, but fail to consider solids with inner voids. In this work we present a methodology based on the handle-decomposition of a manifold that can encode changes in the topology of solids both with and without inner voids. Our methodology uses the Boundary Representation of the solid and a shape similarity criteria to identify changes in the topology of both the outer and inner boundary(ies) of the solid. Our methodology is defined for Morse functions that produce parallel planar level sets and we do not consider the case of annidated solids (i.e. solids within other solids). We present an algorithm to implement our methodology and execute experiments on several datasets. Future work includes the testing of the methodology with functions different to the height function and the speed up of the algorithm's data structure.