vriphys18
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Item Quantitative Validation of Physically Based Deformable Models in Computer Graphics(The Eurographics Association, 2018) Banks, Matthew K.; Hazel, Andrew L.; Riley, Graham D.; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielThis paper presents a novel software framework for quantitative validation of physically-based deformable models in computer graphics. In the majority of previous studies, validation is qualitative (through visual plausibility), which is necessarily user subjective. The proposed framework facilitates construction of a single scalar output that quantifies the agreement between the complete time histories of test and reference models. Different models and comparison metrics can be easily included within the general framework. The framework is shown to yield a high accuracy score for a simplified model that can be analytically derived from the reference model, indicating that the framework is reliable. A lower score results when evaluating a more approximate, yet still visually plausible, model, demonstrating the objective sensitivity of the framework. The software framework can thus provide an objective measure of accuracy and a standardised way to quantitatively compare the accuracy of one method against another, whilst also supplying a quantitative rationale for trading accuracy and performance.Item The Impact of Passive Head-Mounted Virtual Reality Devices on the Quality of EEG Signals(The Eurographics Association, 2018) Cattan, Grégoire; Andreev, Anton; Mendoza, Cesar; Congedo, Marco; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielThanks to the low price, the use of a head-mounted device (HMD) equipped with a smartphone is currently a common set-up for virtual reality (VR). Brain-computer interface (BCI) based on electroencephalography (EEG) is a promising technology to enrich the VR experience. However, the effect of using HMDs on the acquisition of EEG signals remains still unknown. In fact, the smartphone is placed close to the head where EEG sensors are located, thus the smartphoneâ˘AZ´s electronics may perturb the acquisition of the EEG signal. In the present study, we compare the spectral properties of the EEG signal acquired on 12 subjects wearing a SamsungGear HMD equipped with a Samsung S6 smartphone turned on and off. Our study shows that there is no significant difference in the spectral properties of the EEG in these two experimental conditions. We conclude that a smartphone-based HMD is compatible with EEG technology. Some technical problems related to the concurrent use of a HMD and an EEG-based BCI are also discussed.Item Fast Quadrangular Mass-Spring Systems using Red-Black Ordering(The Eurographics Association, 2018) Pall, Pontus; Nylén, Oskar; Fratarcangeli, Marco; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielWe introduce a practical iterative solver for mass-spring systems which can be trivially mapped to massively parallel architectures, in particular GPUs.We employ our solver for the interactive animation of virtual cloth and show that it is computationally fast, robust and scalable, making it suitable for real-time graphics applications. Under the assumption that the input system is represented by a quadrangular network of masses connected by springs, we first partition the particles into two independent sets. Then, during the animation, the dynamics of all the particles belonging to each set is computed in parallel. This enables a full Gauss-Seidel iteration in just two parallel steps, leading to an approximated solution of large mass-spring systems in a few milliseconds. We use our solver to accelerate the solution of the popular Projective Dynamics framework, and compare it with other common iterative solvers in the current literature.Item Real-Time Virtual Pipes Simulation and Modeling for Small-Scale Shallow Water(The Eurographics Association, 2018) Dagenais, Francois; Guzman, Julián; Vervondel, Valentin; Hay, Alexander; Delorme, Sébastien; Mould, David; Paquette, Eric; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielWe propose an approach for real-time shallow water simulation, building upon the virtual pipes model with multi-layered heightmaps. Our approach introduces the use of extended pipes which resolve flow through fully-flooded passages, which is not possible using current multi-layered techniques. We extend the virtual pipe method with a physically-based viscosity model that is both fast and stable. Our viscosity model is integrated implicitly without the expense of solving a large linear system. The liquid is rendered as a triangular mesh surface built from a heightmap. We propose a novel surface optimization approach that prevents interpenetrations of the liquid surface with the underlying terrain geometry. To improve the realism of small-scale scenarios, we present a meniscus shading approach that adjusts the liquid surface normals based on a distance field. Our approach runs in real time on various scenarios of roughly 10 x 10 cm at a resolution of 0.5 mm, with up to five layers.Item VRIPHYS 2018: Frontmatter(Eurographics Association, 2018) Andrews, Sheldon; Erleben, Kenny; Jaillet, Fabrice; Zachmann, Gabriel; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielItem Comparison of Mixed Linear Complementarity Problem Solvers for Multibody Simulations with Contact(The Eurographics Association, 2018) Enzenhöfer, Andreas; Andrews, Sheldon; Teichmann, Marek; Kövecses, József; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielThe trade-off between accuracy and computational performance is one of the central conflicts in real-time multibody simulations, much of which can be attributed to the method used to solve the constrained multibody equations. This paper examines four mixed linear complementarity problem (MLCP) algorithms when they are applied to physical problems involving frictional contact. We consider several different, and challenging, test cases such as grasping, stability of static models, closed loops, and long chains of bodies. The solver parameters are tuned for these simulations and the results are evaluated in terms of numerical accuracy and computational performance. The objective of this paper is to determine the accuracy properties of each solver, find the appropriate method for a defined task, and thus draw conclusions regarding the applicability of each method.Item Laplacian Damping for Projective Dynamics(The Eurographics Association, 2018) Li, Jing; Liu, Tiantian; Kavan, Ladislav; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielDamping is an important ingredient in physics-based simulation of deformable objects. Recent work introduced new fast simulation methods such as Position Based Dynamics and Projective Dynamics. Explicit velocity damping methods currently used in conjunction with Position Based Dynamics or Projective Dynamics are simple and fast, but have some limitations. They may damp global motion or non-physically transport velocities throughout the simulated object. More advanced damping models do not have these limitations, but are slow to evaluate, defeating the benefits of fast solvers such as Projective Dynamics. We present a new type of damping model specifically designed for Projective Dynamics, which provides the quality of advanced damping models while adding only minimal computing overhead. The key idea is to define damping forces using Projective Dynamics' Laplacian matrix. In a number of simulation examples we show that this damping model works very well in practice. When used with a modified Projective Dynamics solver that uses a non-dissipative implicit midpoint integrator, our damping method provides fully user-controllable damping, allowing the user to quickly produce visually pleasing and vivid animations.Item MLS Pressure Extrapolation for the Boundary Handling in Divergence-Free SPH(The Eurographics Association, 2018) Band, Stefan; Gissler, Christoph; Peer, Andreas; Teschner, Matthias; Andrews, Sheldon and Erleben, Kenny and Jaillet, Fabrice and Zachmann, GabrielWe propose a novel method to predict pressure values at boundary particles in incompressible divergence-free SPH simulations (DFSPH). Our approach employs Moving Least Squares (MLS) to predict the pressure at boundary particles. Therefore, MLS computes hyperplanes that approximate the pressure field at the interface between fluid and boundary particles. We compare this approach with two previous techniques. One previous technique mirrors the pressure from fluid to boundary particles. The other one extrapolates the pressure from fluid to boundary particles, but uses a gradient that is computed with Smoothed Particle Hydrodynamics (SPH). We motivate that gradient-based extrapolation is more accurate than mirroring. We further motivate that our proposed MLS gradient is less error prone than the SPH gradient at the boundary. In our experiments, we indicate artifacts in previous approaches. We show that these artifacts are significantly reduced with our approach resulting in simulation steps that can be twice as large compared to previous methods. We further present challenging and complex scenarios to illustrate the capabilities of the proposed boundary handling.