vriphys14

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https://diglib.eg.org/handle/10.2312/7754

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Continuous Collision Detection Between Points and Signed Distance Fields
(The Eurographics Association, 2014) Xu, Hongyi; Barbic, Jernej; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We present an algorithm for fast continuous collision detection between points and signed distance fields. Such robust queries are often needed in computer animation, haptics and virtual reality applications, but have so far only been investigated for polygon (triangular) geometry representations. We demonstrate how to use an octree subdivision of the distance field for fast traversal of distance field cells. We also give a method to combine octree subdivision with points organized into a tree hierarchy, for efficient culling of continuous collision detection tests. We apply our method to multibody rigid simulations, and demonstrate that our method accelerates continuous collision detection between points and distance fields by an order of magnitude.
Controlling the Shape and Motion of Plumes in Explosion Simulations
(The Eurographics Association, 2014) Kawada, Genichi; Kanai, Takashi; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We propose a fluid simulation method with controlling the shape and motion of rising fire and smoke, called plumes, in the incompressible phase of explosion phenomenon. With our method, plumes are generated based on physical phenomenon called entrainment, which strongly characterizes plume behaviors such as rise and circulation. We consider to newly utilize properties characterizing these behavior (physical property). Then, control elements of plume such as rising velocity, size, and the magnitude and position of swirling motions are individually adjusted using these physical properties. With this method, each control element is adjusted by the velocity field which represents the corresponding behavior. By combining all velocity fields and applying those fields to grid-based simulation, plumes can be generated. Our method is unique in that it can both generate and control plumes based on one unified physical model, and this type of model is firstly proposed here. Consequently, our method realizes plumes in the incompressible phase which maintain their physical characteristics as much as possible while being controlled by the user.
Coupling Hair with Smoothed Particle Hydrodynamics Fluids
(The Eurographics Association, 2014) Lin, Wei-Chin; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We present a two-way coupling technique for simulating the complex interaction between hair and fluids. In our approach, the motion of hair and fluids is simulated by evaluating the hydrodynamic forces among them based on boundary handling techniques used in SPH (Smoothed Particle Hydrodynamics) fluids. When hair makes contact with fluids, water absorption inside the hair volume can be simulated with a diffusion process by treating the hair volume as porous media with anisotropic permeability. The saturation of each hair strand is then used to derive the adhesive force between wet hair strands. This enables us to simulate the formation of hair clumps dynamically without the need to employ post clumping processes. The proposed method can be easily applied to any SPH fluid solvers as well as various hair models.
Efficient Transfer of Contact-Point Local Deformations for Data-Driven Simulations
(The Eurographics Association, 2014) Seiler, Martin U.; Spillmann, Jonas; Harders, Matthias; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We present a new approach for data-driven deformation enrichment, which requires a much smaller set of examples. The central idea is to reuse deformation samples. This is done by transferring pre-generated examples from one contact point to another, when the surrounding material as well as the induced deformation are similar. Our similarity notion is derived from two descriptors that use multivariate Hermite polynomials as a basis. The first descriptor comprehends information on the local material density near a contact point, which allows us to segment an object into regions with similar material neighborhoods. At each characteristic location, multiple samples are obtained for different interaction patterns. The obtained information is then encoded in the second descriptor – the deformation descriptor. At run-time, the two descriptors are evaluated at the current contact point. Based on the similarity to the example descriptors, suitable pre-generated data is selected, interpolated, and used to enrich an object surface. We demonstrate our method in several applications and provide quantitative evaluations.
An Improved Jacobi Solver for Particle Simulation
(The Eurographics Association, 2014) Frâncu, Mihai; Moldoveanu, F.; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
This paper presents a new method for simulating particles for computer graphics and video games, based on an improved Jacobi solver and a hybrid approach between velocity time stepping and position based dynamics. Current constrained dynamics solvers use relaxation iterative methods like Gauss-Seidel or Jacobi. We propose a new iterative method based on a minimum residual variant of the Conjugate Gradient algorithm and show that it can be formulated as an improvement to the Jacobi method. We also describe an adaptation of position based dynamics to better handle contact and friction and allow tight two way coupling with velocity level methods.
Information Fusion for Real-time Motion Estimation in Image-guided Breast Biopsy Navigation
(The Eurographics Association, 2014) Kocev, Bojan; Georgii, Joachim; Linsen, Lars; Hahn, Horst Karl; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
A real-time delivery of accurate soft-tissue intervention navigation information is one of the most crucial aspects for accepting the soft-tissue navigation systems for intra-operative use. Currently, soft-tissue navigation systems face some obstacles in terms of registration of the virtual navigation information on the deformable soft-tissue organ. Most of them perform a rigid registration between the virtual data and the organ, and then provide the surgeon with all navigation information. However, they suffer from the disadvantage that the virtual information is not correctly registered to the deformable organ. In order to enable a real-time non-linear registration between the virtual navigation information and the deformable organ, we incorporate different means for tracking the soft- tissue internal and on-surface local motion. Furthermore, we introduce an intelligent information fusion engine for combining the various soft-tissue local motion tracking information into a global motion information channel. The fusion engine is the interface to the motion measurements, a motion dynamics model, and static shape infor- mation, which are combined to compute the a posteriori estimate of the current state of the deformed shape. The dynamics model is realized as a finite-element deformation simulation. In order to test the feasibility of our devised information fusion engine, we have employed it for capturing the global motion of a breast phantom during an image-guided biopsy. The biopsy planning navigation data, in the form of a prior diagnostic MRI, is continuously updated over time according to the a posteriori estimate of the global motion. As a result, the real-time changes in the shape of the breast are always reflected in the biopsy navigation information.
Massively Parallel Batch Neural Gas for Bounding Volume Hierarchy Construction
(The Eurographics Association, 2014) Weller, René; Mainzer, David; Srinivas, Abhishek; Teschner, Matthias; Zachmann, Gabriel; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
Ordinary bounding volume hierarchy (BVH) construction algorithms create BVHs that approximate the boundary of the objects. In this paper, we present a BVH construction that instead approximates the volume of the objects with successively finer levels. It is based on Batch Neural Gas (BNG), a clustering algorithm that is known from machine learning. Additionally, we present a novel massively parallel version of this BNG-based hierarchy construction that runs completely on the GPU. It reduces the theoretical complexity of the sequential algorithm from O(nlogn) to O(log2 n) and also our CUDA implementation outperforms the CPU version significantly in practice.
Massively-Parallel Proximity Queries for Point Clouds
(The Eurographics Association, 2014) Kaluschke, Max; Zimmermann, Uwe; Danzer, Marinus; Zachmann, Gabriel; Weller, Rene; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We present a novel massively-parallel algorithm that allows real-time distance computations between arbitrary 3D objects and unstructured point cloud data. Our main application scenario is collision avoidance for robots in highly dynamic environments that are recorded via a Kinect, but our algorithm can be easily generalized for other applications such as virtual reality. Basically, we represent the 3D object by a bounding volume hierarchy, therefore we adopted the Inner Sphere Trees data structure, and we process all points of the point cloud in parallel using GPU optimized traversal algorithms. Additionally, all parallel threads share a common upper bound in the minimum distance, this leads to a very high culling efficiency. We implemented our algorithm using CUDA and the results show a real-time performance for online captured point clouds. Our algorithm outperforms previous CPU-based approaches by more than an order of magnitude.
Mechanical Modeling of Three-dimensional Plant Tissue Indented by a Probe
(The Eurographics Association, 2014) Malgat, Richard; Boudaoud, Arezki; Faure, François; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
Morphogenesis in a developing organism depends on the mechanics of the structural elements of the organism. In plants, typical experiments involve indenting tissues with a probe and measuring the force needed to reach a given depth. However, the heterogeneous structure and complex geometry of living tissues makes it a challenge to determine how such measurements are related to mechanical properties of the tissue, such as elastic moduli or internal pressure. Indeed, this task requires to perform a large number of direct mechanical simulations with a mesh representing the tissue. Here we propose a framework to achieve this task, using the Simulation Open Framework Architecture (SOFA) platform. We start from a realistic tissue structure corresponding to an early flower bud. We use a mesh where cells are polyhedral-shaped and are made of a liquid under pressure and where the faces separating two cells are thin elastic plates undergoing bending and stretching, and we model the interaction of this mesh with a spherical rigid probe. We obtain force versus depth curves that can be compared to experimental data. Thus our framework enables a comprehensive exploration of how mechanical parameters and probe position influence experimental outcomes, yielding a first step toward understanding the mechanical basis of morphogenesis.
A p-Multigrid Algorithm using Cubic Finite Elements for Efficient Deformation Simulation
(The Eurographics Association, 2014) Weber, Daniel; Mueller-Roemer, Johannes; Altenhofen, Christian; Stork, Andre; Fellner, Dieter W.; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We present a novel p-multigrid method for efficient simulation of co-rotational elasticity with higher-order finite elements. In contrast to other multigrid methods proposed for volumetric deformation, the resolution hierarchy is realized by varying polynomial degrees on a tetrahedral mesh. We demonstrate the efficiency of our approach and compare it to commonly used direct sparse solvers and preconditioned conjugate gradient methods. As the polynomial representation is defined w.r.t. the same mesh, the update of the matrix hierarchy necessary for co-rotational elasticity can be computed efficiently. We introduce the use of cubic finite elements for volumetric deformation and investigate different combinations of polynomial degrees for the hierarchy. We analyze the applicability of cubic finite elements for deformation simulation by comparing analytical results in a static scenario and demonstrate our algorithm in dynamic simulations with quadratic and cubic elements. Applying our method to quadratic and cubic finite elements results in speed up of up to a factor of 7 for solving the linear system.
A Parallel Architecture for IISPH Fluids
(The Eurographics Association, 2014) Thaler, Felix; Solenthaler, Barbara; Gross, Markus; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
We present an architecture for parallel computation of incompressible IISPH simulations on distributed memory systems. We use orthogonal recursive bisection for domain decomposition and present a stable and fast converging load balancing controller. The neighbor search data structure is derived such that it optimally fits into the parallel pipeline. We further show how symmetry aspects of the simulation can be integrated into the architecture. Simultaneous communication and computation are used to minimize parallelization overhead. The seamless integration of these parallel concepts into IISPH results in near linear scaling for large-scale simulations.
Parallel Particles (P2): A Parallel Position Based Approach for Fast and Stable Simulation of Granular Materials
(The Eurographics Association, 2014) Holz, Daniel; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
Granular materials exhibit a large number of diverse physical phenomena which makes their numerical simulation challenging. When set in motion they flow almost like a fluid, while they can present high shear strength when at rest. Those macroscopic effects result from the material's microstructure: a particle skeleton with interlocking particles which stick to and slide across each other, producing soil cohesion and friction. For the purpose of Earthmoving equipment operator training, we developed Parallel Particles (P2), a fast and stable position based granular material simulator which models inter-particle friction and adhesion and captures the physical nature of soil to an extend sufficient for training. Our parallel solver makes the approach scalable and applicable to modern multi-core architectures yielding the simulation speed required in this application. Using a regularization procedure, we successfully model visco-elastic particle interactions on the position level which provides real, physical parameters allowing for intuitive tuning. We employ the proposed technique in an Excavator training simulator and demonstrate that it yields physically plausible results at interactive to real-time simulation rates.
SutureHap: A Suture Simulator with Haptic Feedback
(The Eurographics Association, 2014) Ricardez, Eusebio; Noguez, Julieta; Neri, Luis; Munoz-Gomez, Lourdes; Escobar-Castillejos, David; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
Surgical procedures require a high degree of complexity and difficulty. Consequently, extensive preparation in the learning process of medical students is necessary in order to perform suturing tasks successfully. Some authors suggest that a minimum of 750 operations are needed to acquire the experience to perform correctly surgical procedures. Moreover, current laws establish standards if corpses and animals are used as medical learning environments; as a result, the development of skills and processes is hindered. This paper introduces the development of a virtual environment for training suture skills: SutureHap, which uses two Sensable Phantom Omni haptic devices. To create a proper simulation of the human skin which must fulfill graphic and physical characteristics, NVIDIA PhysX libraries were usea. Some of these libraries were originally defined to represent cloths; however, in this work some parameters were adjusted to obtain the desired simulation. An architecture that facilitates the integration of haptic devices was designed. A simplified method of collision detection and haptic feedback generation was created. This enabled the reduction of complexity generated during collision detection, and it diminished the time to develop the virtual environment. Tweezers, thread and needle models were added in the virtual environment. Due to fact that PhysX exploits GPU processing, response time was improved during modeling of the skin. Additionally, suturing tasks were designed by taking into consideration real procedures made by medical experts. The acquisition of skills and competencies in suture process are increased through haptic devices due to the fact that they can send tactile sensations. These environments decrease costs and risks, and provide real sensations as the ones that can be perceived in current learning environments. Finally, an evaluation focused on the perception of this environment was made by students. Preliminary results are promising, and it is expected that this environment facilitates the acquisition of suture skills.
A Unified Topological-Physical Model for Adaptive Refinement
(The Eurographics Association, 2014) Fléchon, Elsa; Zara, Florence; Damiand, Guillaume; Jaillet, Fabrice; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
In Computer Graphics, physically-based simulation of deformable objects is a current challenge, and many efficient models have been developed to reach real-time performance. However, these models are often limited when complex interactions involving topological modifications are required. To overcome this, the key issue is to manage concurrently, and at minimal cost, both the topology and physical properties. Thus, this paper presents a unified topological-physical model for soft body simulation. The complete embedding of physical and topological models will facilitate operations like piercing, fracture or cutting, as well as adaptive refinement. Indeed, the difficulty is to treat topological changes during the simulation, requiring combined geometric and physics considerations. Rigorous topological operations guarantee the validity of the mesh, while direct access to the adjacent and incident relations will ease the update of physical properties of new elements created during these operations. These features are illustrated on an embedded mass-spring system undergoing topological modifications performed during simulation. Different levels of subdivision are also presented.
Virtual Fitting Pipeline: Body Dimension Recognition, Cloth Modeling, and On-Body Simulation
(The Eurographics Association, 2014) Siegmund, Dirk; Samartzidis, Timotheos; Damer, Naser; Nouak, Alexander; Busch, Christoph; Jan Bender and Christian Duriez and Fabrice Jaillet and Gabriel Zachmann
This paper describes a solution for 3D clothes simulation on human avatars. The proposed approach consists of three parts, the collection of anthropometric human body dimensions, cloths scanning, and the simulation on 3D avatars. The simulation and human machine interaction has been designed for application in a passive In- Shop advertisement system. All parts have been evaluated and adapted under the aim of developing a low-cost automated scanning and post-production system. Human body dimension recognition was achieved by using a landmark detection based approach using both two 2D and 3D cameras for front and profile images. The human silhouettes extraction solution based on 2D images is expected to be more robust to multi-textured background surfaces than existing solutions. Eight measurements corresponding to the norm of body dimensions defined in the standard EN-13402 were used to reconstruct a 3D model of the human body. The performance is evaluated against the ground-truth of our newly acquired database. For 3D scanning of clothes, different scanning methods have been evaluated under apparel, quality and cost aspects. The chosen approach uses state of the art consumer products and describes how they can be combined to develop an automated system. The scanned cloths can be later simulated on the human avatars, which are created based on estimation of human body dimensions. This work concludes with software design suggestions for a consumer oriented solution such as a virtual fitting room using body metrics. A number of future challenges and an outlook for possible solutions are also discussed.

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