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Item Study of the Influence of User Characteristics on the Virtual Reality Presence(The Eurographics Association, 2018) Mayor, Jesús; Sánchez, Alberto; Raya, Laura; García-Fernández, Ignacio and Ureña, CarlosIn recent years, virtual reality has grown a lot in different areas of application, including ludic, social and research, being used by a large and growing number of users with different profiles. Presence is one of the most distinctive and important features of a virtual reality experience. The aim of this article is to study the most suitable areas of application for users and to analyze the influence of different characteristics of the user's profile in the perceived presence. We have tested the interest applications indicated by 159 subjects and we have designed an immersive virtual reality experience, testing the behavior and performance of 48 users. The results obtained show that gender can influence the perceptual sensation of presence in these types of virtual environments.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 Modelling the Fluid-Boundary Interaction in SPH(The Eurographics Association, 2018) Perea, Juan J.; Cordero, Juan M.; García-Fernández, Ignacio and Ureña, CarlosSmoothed Particle Hydrodynamics (SPH) is a numerical method based on mutually interacting meshfree particles, and has been widely applied to fluid simulation in Computer Graphics. Originally SPH does not define the behaviour of the particle system in the contour, so the different variants of SPH have been solving this deficiency with different techniques. Some of these techniques are based on fictitious forces, specular particles or semi-analytic fields. However, all these proposals present a drawback, that are may introduce additional inaccuracy as a divergent behaviour of the particle dynamics or an artificial separation between the fluid limits and the contour. To solve these limitations at this paper presents a new technique based on contour particles that are used during simulation to model the interaction with the fluid. The use of contour particles had already been used in other works to construct the contour like a particle layer. That solution presents problems especially when increasing the complexity of the contour shape. In addition, unlike other techniques, this paper presents an additional advantage, the possibility of obtaining all the dynamic magnitudes for improving efficiency and versatility.Item An Optimized Marker Layout for 3D Facial Motion Capture(The Eurographics Association, 2018) Will, A. D.; Martino, J. M. De; Bezerra, J.; Livesu, Marco and Pintore, Gianni and Signoroni, AlbertoFacial motion capture (Facial Mocap) has gained increasing attention from researchers and professionals from different areas of interest, including entertainment, face-to-face communication, and training. Facial Mocap allows straightforward capture of dynamic behavior of the face from live action, providing data that can be used to drive realistic animation of a 3D virtual face. Facial Mocap is an advantageous alternative to the direct and laborious manipulation of the face model. In particular, marker-based mocap technique acquires three-dimensional facial points trajectories by tracking markers fixed on the face of an actor. However, despite the existence of several empirical facial marker layouts, the ideal positioning of the markers is still an open question. This paper presents an optimization technique to calculate the quantity and positioning facial markers and establish their influences on the polygon mesh based on the correlation of markers in a dense layout. The technique generates an optimized marker layout discarding unnecessary markers and positioning the remaining ones.Item A Prototype of Virtual Reality System for the Visualization, Exploration and Modeling of Huge Point Clouds(The Eurographics Association, 2018) Ortega-Donaire, José; Segura-Sánchez, Rafael Jesús; Ogáyar-Anguita, Carlos-Javier; Rueda-Ruiz, Antonio Jesús; García-Fernández, Ignacio and Ureña, CarlosThe use of specific techniques for the management and visualization of huge point clouds is necessary to solve the drawbacks of inefficiency derived from the size of the dataset and the techniques used to visualize it. This work presents a prototype of VR system for the visualization and management of extensive point clouds in 3D with the ability to edit specific points. For this, the tool incorporates multiresolution techniques, which improve the performance and efficiency of the system. The prototype also incorporates the management of the point cloud stored in an unstructured database; so the prototype can request parts of the dataset from the required fractions generated by an octree. This allows the progressive processing of 3D point clouds, which is very useful to control and visualize a large data set in real time.Item Rendering and Interacting With Volume Models in Immersive Environments(The Eurographics Association, 2018) Fons, Joan; Monclús, Eva; Vázquez, Pere-Pau; Navazo, Isabel; García-Fernández, Ignacio and Ureña, CarlosThe recent advances in VR headsets, such as the Oculus Rift or HTC Vive, at affordable prices offering a high resolution display, has empowered the development of immersive VR applications. data. In this paper we propose an immersive VR system that uses some well-known acceleration algorithms to achieve real-time rendering of volumetric datasets in an immersive VR system. Moreover, we have incorporated different basic interaction techniques to facilitate the inspection of the volume dataset. The interaction has been designed to be as natural as possible in order to achieve the most comfortable, user-friendly virtual experience. We have conducted an informal user study to evaluate the user preferences. Our evaluation shows that our application is perceived usable, easy of learn and very effective in terms of the high level of immersion achieved.Item CageLab: an Interactive Tool for Cage-Based Deformations(The Eurographics Association, 2018) Casti, S.; Corda, F.; Livesu, M.; Scateni, R.; Livesu, Marco and Pintore, Gianni and Signoroni, AlbertoPosing a digital character by acting on the vertices of a coarse control cage is, after skeleton-based, probably the most widely used technique for digital animation. While skeleton-based techniques have been deeply researched and a variety of industrial and academic tools are available for it, cage-based techniques have historically received less attention. In recent years we observed an increasing interest in the field, which results in a growing number of publications both on algorithms for automatic or semi-automatic cage generation, and for smooth barycentric coordinates for general polyhedral meshes. We introduce CageLab: a novel research-oriented software tool that allows scholars and practitioners in general to get acquainted with cagebased animation in a lightweight and easy to use environment. Users can: (i) load digital characters and their associated cages, applying character deformations with a selection of the most widely used barycentric coordinates available in literature; (ii) compare alternative cages for a given digital character; (iii) compare alternative barycentric coordinates w.r.t their smoothness and locality within the cage; (iv) use CageLab for educational purposes, or to produce images and videos for scientific articles. We publicly release the tool to the community, with the hope to support this growth, and possibly foster even more research in the field.Item A Study on Natural 3D Shape Manipulation in VR(The Eurographics Association, 2018) Cordeiro, E.; Giannini, F.; Monti, M.; Mendes, D.; Ferreira, A.; Livesu, Marco and Pintore, Gianni and Signoroni, AlbertoCurrent immersive modeling environments use non-natural tools and interfaces to support traditional shape manipulation operations. In the future, we expect the availability of natural methods of interaction with 3D models in immersive environments to become increasingly important in several industrial applications. In this paper, we present a study conducted on a group of potential users with the aim of verifying if there is a common strategy in gestural and vocal interaction in immersive environments when the objective is modifying a 3D shape model. The results indicate that users adopt different strategies to perform the different tasks but in the execution of a specific activity it is possible to identify a set of similar and recurrent gestures. In general, the gestures made are physically plausible. During the experiment, the vocal interaction was used quite rarely and never to express a command to the system but rather to better specify what the user was doing with gestures.Item Muscle Simulation with Extended Position Based Dynamics(The Eurographics Association, 2018) Romeo, Marco; Monteagudo, Carlos; Sánchez-Quirós, Daniel; García-Fernández, Ignacio and Ureña, CarlosRecent research on muscle simulation for Visual Effects relies on numerical methods such as the Finite Element Method or Finite Volume Method. These approaches produce realistic results, but require high computational time and are complex to set up. On the other hand Position Based Dynamics offers a fast and controllable solution to simulate surfaces and volumes, but there is no literature on how to implement constraints that could be used to realistically simulate muscles for digital creatures with this method. In this paper we extend the current state-of-the-art in Position Based Dynamics to efficiently compute realistic skeletal-muscle simulation. In particular we embed muscle fibers in the solver by adding an anisotropic component to the distance constraints between mesh points and apply overpressure to realistically model muscle volume changes under contraction. We also present a technique that consistently provides an internal structure for our muscle volumes. We use this structure to preserve the shape and extract relevant information for the activation of the muscle fibers. Finally, we propose a modification of the Extended Position Based Dynamics algorithm and describe other details for proper simulation of character’'s muscle dynamics.Item Evolutionary Interactive Analysis of MRI Gastric Images Using a Multiobjective Cooperative-coevolution Scheme(The Eurographics Association, 2018) Al-Maliki, Shatha F.; Lutton, Évelyne; Boué, François; Vidal, Franck; {Tam, Gary K. L. and Vidal, FranckIn this study, we combine computer vision and visualisation/data exploration to analyse magnetic resonance imaging (MRI) data and detect garden peas inside the stomach. It is a preliminary objective of a larger project that aims to understand the kinetics of gastric emptying. We propose to perform the image analysis task as a multi-objective optimisation. A set of 7 equally important objectives are proposed to characterise peas. We rely on a cooperation co-evolution algorithm called 'Fly Algorithm' implemented using NSGA-II. The Fly Algorithm is a specific case of the 'Parisian Approach' where the solution of an optimisation problem is represented as a set of individuals (e.g. the whole population) instead of a single individual (the best one) as in typical evolutionary algorithms (EAs). NSGA-II is a popular EA used to solve multi-objective optimisation problems. The output of the optimisation is a succession of datasets that progressively approximate the Pareto front, which needs to be understood and explored by the end-user. Using interactive Information Visualisation (InfoVis) and clustering techniques, peas are then semi-automatically segmented.