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Item Elasticity-based Clustering for Haptic Interaction with Heterogeneous Deformable Objects(The Eurographics Association, 2017) Gouis, Benoît Le; Marchal, Maud; Lécuyer, Anatole; Arnaldi, Bruno; Fabrice Jaillet and Florence ZaraPhysically-based simulation of heterogeneous objects remains computationally-demanding for many applications, especially when involving haptic interaction with virtual environments. In this paper, we introduce a novel multiresolution approach for haptic interaction with heterogeneous deformable objects. Our method called "Elasticity-based Clustering" is based on the clustering and aggregation of elasticity inside an object, in order to create large homogeneous volumes preserving important features of the initial distribution. The design of such large and homogeneous volumes improves the attribution of elasticity to the elements of the coarser geometry. We could successfully implement and test our approach within a complete and real-time haptic interaction pipeline compatible with consumer-grade haptic devices. We evaluated the performance of our approach on a large set of elasticity configurations using a perception-based quality criterion. Our results show that for 90% of studied cases our method can achieve a 6 times speedup in the simulation time with no theoretical perceptual difference.Item Towards Biomechanically and Visually Plausible Volumetric Cutting Simulation of Deformable Bodies(The Eurographics Association, 2019) Qian, Yinling; Huang, Wenbin; Si, Weixin; Liao, Xiangyun; Wang, Qiong; Heng, Pheng-Ann; Lee, Jehee and Theobalt, Christian and Wetzstein, GordonDue to the simplicity and high efficiency, composited finite element method(CFEM) based virtual cutting attracted much attention in the field of virtual surgery in recent years. Even great progress has been made in volumetric cutting of deformable bodies, there are still several open problems restricting its applications in practical surgical simulator. First among them is cutting fracture modelling. Recent methods would produce cutting surface immediately after an intersection between the cutting plane and the object. But in real cutting, biological tissue would first deform under the external force induced by scalpel and then fracture occurs when the stress exceeds a threshold. Secondly, it's computation-intensive to reconstruct cutting surface highly consistent with the scalpel trajectory, since reconstructed cutting surface in CFEM-based virtual cutting simulation is grid-dependent and the accuracy of cutting surface is proportional to the grid resolution. This paper propose a virtual cutting method based on CFEM which can effectively simulate cutting fracture in a biomechanically and visually plausible way and generate cutting surface which is consistent with the scalpel trajectory with a low resolution finite element grid. We model this realistic cutting as a deformation-fracture repeating process. In deformation stage, the object will deform along with the scalpel motion, while in the fracture stage cutting happens and a cutting surface will be generated from the scalpel trajectory. A delayed fracturing criteria is proposed to determine when and how the cutting fracture occurs and an influence domain adaptation method is employed to generate accurate cutting surface in both procedures of deformation and fracture. Experiments show that our method can realistically simulate volumetric cutting of deformable bodies and efficiently generate accurate cutting surface thus facilitating interactive applications.Item A Virtual Character Posing System based on Reconfigurable Tangible User Interfaces and Immersive Virtual Reality(The Eurographics Association, 2018) Cannavò, A.; Lamberti, F.; Livesu, Marco and Pintore, Gianni and Signoroni, AlbertoComputer animation and, particularly, virtual character animation, are very time consuming and skill-intensive tasks, which require animators to work with sophisticated user interfaces. Tangible user interfaces (TUIs) already proved to be capable of making character animation more intuitive, and possibly more efficient, by leveraging the affordances provided by physical props that mimic the structure of virtual counterparts. The main downside of existing TUI-based animation solutions is the reduced accuracy, which is due partly to the use of mechanical parts, partly to the fact that, despite the adoption of a 3D input, users still have to work with a 2D output (usually represented by one or more views displayed on a screen). However, output methods that are natively 3D, e.g., based on virtual reality (VR), have been already exploited in different ways within computer animation scenarios. By moving from the above considerations and by building upon an existing work, this paper proposes a VR-based character animation system that combines the advantages of TUIs with the improved spatial awareness, enhanced visualization and better control on the observation point in the virtual space ensured by immersive VR. Results of a user study with both skilled and unskilled users showed a marked preference for the devised system, which was judged as more intuitive than that in the reference work, and allowed users to pose a virtual character in a lower time and with a higher accuracy.Item Evaluating and Comparing Game-controller based Virtual Locomotion Techniques(The Eurographics Association, 2017) Sarupuri, Bhuvaneswari; Hoermann, Simon; Whitton, Mary C.; Lindeman, Robert W.; Robert W. Lindeman and Gerd Bruder and Daisuke IwaiThe incremental hardware costs of virtual locomotion are minimized when the technique uses interaction capabilities available in controllers and devices that are already part of the VE system, e.g., gamepads, keyboards, and multi-function controllers. We used a different locomotion technique for each of these three devices: gamepad thumb-stick (joystick walking), a customized hybrid keyboard for gaming (speedpad walking), and an innovative technique that uses the orientation and triggers of the HTC Vive controllers (TriggerWalking). We explored the efficacy of locomotion techniques using these three devices in a hide and seek task in an indoor environment. We measured task performance, simulator sickness, system usability, perceived workload, and preference. We found that users had a strong preference for TriggerWalking, which also had the least increase in simulator sickness, the highest performance score, and highest perceived usability. However, participants using TriggerWalking also had the most object and wall-collisions. Overall we found that TriggerWalking is an effective locomotion technique and that is has significant and important benefits. Future research will explore if TriggerWalking can be used with equal benefits in other virtual-environments, on different tasks, and types of movement.Item Velocity-Based LOD Reduction in Virtual Reality: A Psychophysical Approach(The Eurographics Association, 2023) Petrescu, David; Warren, Paul A.; Montazeri, Zahra; Pettifer, Steve; Babaei, Vahid; Skouras, MelinaVirtual Reality headsets enable users to explore the environment by performing self-induced movements. The retinal velocity produced by such motion reduces the visual system's ability to resolve fine detail. We measured the impact of self-induced head rotations on the ability to detect quality changes of a realistic 3D model in an immersive virtual reality environment. We varied the Level of Detail (LOD) as a function of rotational head velocity with different degrees of severity. Using a psychophysical method, we asked 17 participants to identify which of the two presented intervals contained the higher quality model under two different maximum velocity conditions. After fitting psychometric functions to data relating the percentage of correct responses to the aggressiveness of LOD manipulations, we identified the threshold severity for which participants could reliably (75%) detect the lower LOD model. Participants accepted an approximately four-fold LOD reduction even in the low maximum velocity condition without a significant impact on perceived quality, suggesting that there is considerable potential for optimisation when users are moving (increased range of perceptual uncertainty). Moreover, LOD could be degraded significantly more (around 84%) in the maximum head velocity condition, suggesting these effects are indeed speed-dependent.Item LoBSTr: Real-time Lower-body Pose Prediction from Sparse Upper-body Tracking Signals(The Eurographics Association and John Wiley & Sons Ltd., 2021) Yang, Dongseok; Kim, Doyeon; Lee, Sung-Hee; Mitra, Niloy and Viola, IvanWith the popularization of games and VR/AR devices, there is a growing need for capturing human motion with a sparse set of tracking data. In this paper, we introduce a deep neural network (DNN) based method for real-time prediction of the lowerbody pose only from the tracking signals of the upper-body joints. Specifically, our Gated Recurrent Unit (GRU)-based recurrent architecture predicts the lower-body pose and feet contact states from a past sequence of tracking signals of the head, hands, and pelvis. A major feature of our method is that the input signal is represented by the velocity of tracking signals. We show that the velocity representation better models the correlation between the upper-body and lower-body motions and increases the robustness against the diverse scales and proportions of the user body than position-orientation representations. In addition, to remove foot-skating and floating artifacts, our network predicts feet contact state, which is used to post-process the lower-body pose with inverse kinematics to preserve the contact. Our network is lightweight so as to run in real-time applications. We show the effectiveness of our method through several quantitative evaluations against other architectures and input representations with respect to wild tracking data obtained from commercial VR devices.Item Experiencing High-Speed Slash Action in Virtual Reality Environment(The Eurographics Association, 2022) Yamamoto, Toranosuke; Fukuchi, Kentaro; Theophilus Teo; Ryota KondoWhen a user uses a hand controller to swing a virtual sword in a virtual space, the sword movement seems slow if the its trajectory reflects the input directly. We hypothesize that this is because we are accustomed to seeing fast and instantaneous motion through movies or animations, and thus we perceive their motion as relatively slow. To address this issue, we propose a novel method of displaying exaggerated sword motions to allow a virtual reality user to enjoy a fast slash action. This method displays an arc-shaped motion blur effect along the predicted motion when the system detects the start of the slashing motion until the hand controller motion stops. Graphics of the sword are not displayed during this time. Therefore, the user is unaware of the actual trajectory of their input and how far it differs from the exaggerated motion blur effect.Item Variational Pose Prediction with Dynamic Sample Selection from Sparse Tracking Signals(The Eurographics Association and John Wiley & Sons Ltd., 2023) Milef, Nicholas; Sueda, Shinjiro; Kalantari, Nima Khademi; Myszkowski, Karol; Niessner, MatthiasWe propose a learning-based approach for full-body pose reconstruction from extremely sparse upper body tracking data, obtained from a virtual reality (VR) device. We leverage a conditional variational autoencoder with gated recurrent units to synthesize plausible and temporally coherent motions from 4-point tracking (head, hands, and waist positions and orientations). To avoid synthesizing implausible poses, we propose a novel sample selection and interpolation strategy along with an anomaly detection algorithm. Specifically, we monitor the quality of our generated poses using the anomaly detection algorithm and smoothly transition to better samples when the quality falls below a statistically defined threshold. Moreover, we demonstrate that our sample selection and interpolation method can be used for other applications, such as target hitting and collision avoidance, where the generated motions should adhere to the constraints of the virtual environment. Our system is lightweight, operates in real-time, and is able to produce temporally coherent and realistic motions.Item Immersive Analytics of Heterogeneous Biological Data Informed through Need-finding Interviews(The Eurographics Association, 2021) Ripken, Christine; Tusk, Sebastian; Tominski, Christian; Vrotsou, Katerina and Bernard, JürgenThe goal of this work is to improve existing biological analysis processes by means of immersive analytics. In a first step, we conducted need-finding interviews with 12 expert biologists to understand the limits of current practices and identify the requirements for an enhanced immersive analysis. Based on the gained insights, a novel immersive analytics solution is being developed that enables biologists to explore highly interrelated biological data, including genomes, transcriptomes, and phenomes. We use an abstract tabular representation of heterogeneous data projected onto a curved virtual wall. Several visual and interactive mechanisms are offered to allow biologists to get an overview of large data, to access details and additional information on the fly, to compare selected parts of the data, and to navigate up to about 5 million data values in real-time. Although a formal user evaluation is still pending, initial feedback indicates that our solution can be useful to expert biologists.Item Effect of Avatar Anthropomorphism on Body Ownership, Attractiveness and Collaboration in Immersive Virtual Environments(The Eurographics Association, 2020) Gorisse, Geoffrey; Dubosc, Charlotte; Christmann, Olivier; Fleury, Sylvain; Poinsot, Killian; Richir, Simon; Argelaguet, Ferran and McMahan, Ryan and Sugimoto, MakiEffective collaboration in immersive virtual environments requires to be able to communicate flawlessly using both verbal and non-verbal communication. We present an experiment investigating the impact of anthropomorphism on the sense of body ownership, avatar attractiveness and performance in an asymmetric collaborative task. Using three avatars presenting different facial properties, participants have to solve a construction game according to their partner's instructions. Results reveal no significant difference in terms of body ownership, but demonstrate significant differences concerning attractiveness and completion duration of the collaborative task. However the relative verbal interaction duration seems not impacted by the anthropomorphism level of the characters, meaning that participants were able to interact verbally independently of the way their character physically express their words in the virtual environment. Unexpectedly, correlation analyses also reveal a link between attractiveness and performance. The more attractive the avatar, the shorter the completion duration of the game. One could argue that, in the context of this experiment, avatar attractiveness could have led to an improvement in non-verbal communication as users could be more prone to observe their partner which translates into better performance in collaborative tasks. Other experiments must be conduced using gaze tracking to support this new hypothesis.