vriphys12

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https://diglib.eg.org/handle/10.2312/1025

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OCTAVIS: An Easy-to-Use VR-System for Clinical Studies
(The Eurographics Association, 2012) Dyck, Eugen; Zell, Eduard; Kohsik, Agnes; Grewe, Philip; Winter, York; Piefke, Martina; Botsch, Mario; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
We present the OCTAVIS system, a novel virtual reality platform developed for rehabilitation and training of patients with brain function disorders. To meet the special requirements of clinical studies, our system has been designed with ease of use, patient safety, ease of maintenance, space and cost efficiency in mind. Patients are sitting on a rotating office chair in the center of eight touch screen displays arranged in octagon around them, thereby providing a 360 horizontal panorama view. Navigation is intuitively controlled through chair rotation and a joystick in the armrest. A touch interface enables easy object selection. The OCTAVIS system has been successfully deployed to four hospitals. We report first results of clinical studies conducted with patients and control groups, demonstrating that our system is immersive, easy to use, and supportive for rehabilitation purposes.
Real-Time Motion Synthesis for Multiple Goal-Directed Tasks Using Motion Layers
(The Eurographics Association, 2012) Mousas, Christos; Newbury, Paul; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
In this paper, a work in progress approach of layered motion interpolation method for designing realistic animation sequences for multiple goal-directed tasks is presented. The proposed solution is based on the ability to extract and synthesize different motions (in layers), while trying to efficiently reconstruct a natural-looking character's posture in real time. The proposed solution is examined for the case in which running, jumping, and reaching motions are combined. However, in addressing multiple goals fulfilled by a character in complex environments, as well as those involving complex motions, it is necessary to define the best way to handle and reconstruct the information from a motion capture database. Finally, because the character's posture should be as natural looking as possible, a simple centre of mass approach is proposed, to give desirable results at specific time steps.
Physics-based Augmented Reality for 3D Deformable Object
(The Eurographics Association, 2012) Haouchine, Nazim; Dequidt, Jérémie; Kerrien, Erwan; Berger, Marie-Odile; Cotin, Stéphane; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
This paper introduces an original method to perform augmented or mixed reality on deformable objects. Compared to state-of-the-art techniques, our method is able to track deformations of volumetric objects and not only surfacic objects. A flexible framework that relies on the combination of a 3D motion estimation and a physicsbased deformable model used as a regularization and interpolation step allows to perform a non-rigid and robust registration. Results are exposed, based on computer-generated datasets and video sequences of real environments in order to assess the relevance of our approach.
Bézier Shell Finite Element for Interactive Surgical Simulation
(The Eurographics Association, 2012) Golembiovský, Tomá¹; Duriez, Christian; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
There is a strong need, in surgical simulations, for physically based deformable model of thin or hollow structures. The use of shell theory allows to have a well-founded formulation resulting from continuum mechanics of thin objects. However, this formulation asks for second order spatial derivatives so requires the use of complex elements. In this paper, we present a new way of building the interpolation: First, we use the trianular cubic Bézier shell to allow for a good continuity inside and between the elements and second, we build a kinematic mapping to reduce the degrees of freedom of the element from 10 control points with 3 Degrees of Freedom (
High-Resolution Simulation of Granular Material with SPH
(The Eurographics Association, 2012) Ihmsen, Markus; Wahl, Arthur; Teschner, Matthias; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
We present an efficient framework for simulating granular material with high visual detail. Our model solves the computationally and numerically critical forces on a coarsely sampled particle simulation. We incorporate a new frictional boundary force into an existing continuum-based method which enables realistic interactions and a more robust simulation. Visual realism is achieved by coupling a set of highly resolved particles with the base simulation at low computational costs. Thereby, visual details can be added which are not resolved by the base simulation.
Fast Simulation of Inextensible Hair and Fur
(The Eurographics Association, 2012) Müller, Matthias; Kim, Tae-Yong; Chentanez, Nuttapong; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
In this short paper we focus on the fast simulation of hair and fur on animated characters. While it is common in films to simulate single hair strands on virtual humans and on furry animals, those features are either not present on characters in computer games or modeled with simplified textured meshes. The main difficulty of simulating hair in real time applications is the sheer number of hair strands and the fact that each hair is inextensible. Keeping thousands of deformable objects from being stretched is computationally expensive. In this paper, we present a robust method for simulating hair and fur that guarantees inextensiblity with a single iteration per frame. For an iteration count this low, existing methods either become unstable or introduce a substantial amount of stretching. Our method is geometric in nature and able to simulate thousands of inextensible hair strands in real time.
Generic Spine Model with Simple Physics for Life-Like Quadrupeds and Reptiles
(The Eurographics Association, 2012) Karim, Ahmad Abdul; Meyer, Alexandre; Gaudin, Thibaut; Buendia, Axel; Bouakaz, Saida; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
We propose a pseudo-physics system and a spine model that can be coupled to generate life-like locomotion animations of quadrupeds and reptiles. The pseudo-physics system uses minimalist particle-based physics and values of the gait pattern to generate the sinusoidal-like ballistic movement of the pelvis observed in nature. While the spine model uses simple geometry-based calculations and 3D Hermite curves to generate a flexible spine model, giving the animated creatures more agility. Our final system is totally controllable by the user in order to generate any desired style.
A Packed Memory Array to Keep Moving Particles Sorted
(The Eurographics Association, 2012) Durand, Marie; Raffin, Bruno; Faure, François; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
Neighbor identification is the most computationally intensive step in particle based simulations. To contain its cost, a common approach consists in using a regular grid to sort particles according to the cell they belong to. Then, neighbor search only needs to test the particles contained in a constant number of cells. During the simulation, a usually small amount of particles are moving between consecutive steps. Taking into account this temporal coherency to save on the maintenance cost of the acceleration data structure is dificult as it usually triggers costly dynamics memory allocations or data moves. In this paper we propose to rely on a Packed Memory Array (PMA) to effciently keep particles sorted according to their cell index. The PMA maintains gaps in the particle array that enable to keep particle sorted with O(log<sup>2</sup>(n)) amortized data moves. We further improve the original PMA data structure to support eficient batch data moves. Experiments show that the PMA can outperform a compact sorted array for up to 50% element moves.
An Implicit Tensor-Mass Solver on the GPU for Soft Bodies Simulation
(The Eurographics Association, 2012) Faure, Xavier; Zara, Florence; Jaillet, Fabrice; Moreau, Jean-Michel
The realistic and interactive simulation of deformable objects has become a challenge in Computer Graphics. In this paper, we propose a GPU implementation of the resolution of the mechanical equations, using a semi-implicit as well as an implicit integration scheme. At the contrary of the classical FEM approach, forces are directly computed at each node of the discretized objects, using the evaluation of the strain energy density of the elements. This approach allows to mix several mechanical behaviors in the same object. Results show a notable speedup of 30, especially in the case of complex scenes. Running times shows that this efficient implementation may contribute to make this model more popular for soft bodies simulations.
Synthesizing Balancing Character Motions
(The Eurographics Association, 2012) Kenwright, Ben; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
This paper presents a novel method for generating balancing character poses by means of a weighted inverse kinematic constraint algorithm. The weighted constraints enable us to control the order of priority so that more important conditions such as balancing can take priority over less important ones. Maintaining a balancing pose enables us to create a variety of physically accurate motions (e.g., stepping, crouching). Balancing is achieved by controlling the location of the overall centre of mass of an articulated character; while the secondary constraints generate poses from end-effectors and trajectory information to provide continuous character movement. The poses are created by taking into account physical properties of the articulated character, that include joint mass, size, strength and angular limits. We demonstrate the successfulness of our method by generating balancing postures that are used to produce controllable character motions with physically accurate properties; likewise, our method is computationally fast, flexible and straightforward to implement.
Efficient Breast Deformation Simulation
(The Eurographics Association, 2012) Harz, Markus T.; Georgii, Joachim; Wang, Lei; Schilling, Kathy; Peitgen, Heinz-Otto; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
Breast surgery might benefit from image guidance, if position and extend of the disease could be visualized in the same breast deformation as the surgery is performed. Such visualizations, however, are challenging to obtain, since the positioning for image acquisition in MRI is prone, while the patient lies supine for surgical procedures, causing a considerable deformation of the breasts between the two states. In our contribution, we outline a set of novel algorithms and methods to improve an efficient simulation of breast deformation between the prone image and the supine surgery positioning. In particular, we propose several extensions to a highly efficient dynamic corotated finite element method (FEM), namely non-linear material properties, the sliding of the breast tissue on the chest wall, and a fine-tuning step to align the breast model to a measured surface. All extensions are carefully designed to keep the efficiency and stability of the approach, and thus to allow their application in clinical routine. We explore all novel techniques using synthetic and volunteer prone and supine breast MRI data and assess their feasibility towards accurate, yet efficient simulation of large breast deformations.
An Efficient Surface Reconstruction Pipeline for Particle-Based Fluids
(The Eurographics Association, 2012) Akinci, Gizem; Akinci, Nadir; Ihmsen, Markus; Teschner, Matthias; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
In this paper we present an efficient surface reconstruction pipeline for particle-based fluids such as smoothed particle hydrodynamics. After the scalar field computation and the marching cubes based triangulation, we post process the surface mesh by applying surface decimation and subdivision algorithms. In comparison to existing approaches, the decimation step alleviates the particle alignment related bumpiness very efficiently and reduces the number of triangles in flat regions. Later, the subdivision step ensures that the non-smooth regions are smoothed in a performance friendly way which allows our approach to run significantly faster by using lower resolution marching cubes grids. The presented pipeline is applicable to particle position data sets in a frame by frame basis. Throughout the paper, we present both visual and performance comparisons with different parameter settings, and with a state-of-the-art surface reconstruction technique. Our results demonstrate that in comparison to other approaches with comparable surface quality, our pipeline runs 15 to 20 times faster with up to 80% less memory and secondary storage consumption.
3D Mobility Learning and Regression of Articulated, Tracked Robotic Vehicles by Physics-based Optimization
(The Eurographics Association, 2012) Papadakis, Panagiotis; Pirri, Fiora; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
Motion planning for robots operating on 3D rough terrain requires the synergy of various robotic capabilities, from sensing and perception to simulation, planning and prediction. In this paper, we focus on the higher level of this pipeline where by means of physics-based simulation and geometric processing we extract the information that is semantically required for an articulated, tracked robot to optimally traverse 3D terrain. We propose a model that quantifies 3D traversability by accounting for intrinsic robot characteristics and articulating capabilities together with terrain characteristics. By building upon a set of generic cost criteria for a given robot state and 3D terrain patch, we augment the traversability cost estimation by: (i) unifying pose stabilization with traversability cost estimation, (ii) introducing new parameters into the problem that have been previously overlooked and (iii) adapting geometric computations to account for the complete 3D robot body and terrain surface. We apply the proposed model on a state-of-the-art Search and Rescue robot by performing a plurality of tests under varying conditions and demonstrate its efficiency and applicability in real-time.
Real-time Hair Simulation with Efficient Hair Style Preservation
(The Eurographics Association, 2012) Han, Dongsoo; Harada, Takahiro; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
Hair can be a prominent feature of characters in real-time games. In this paper, we propose hair simulation with efficient preservation of various hair styles. Bending and twisting effects are crucial to simulate curly or wavy hair. We propose local and global shape constraints and parallel methods to update local and global transforms to find goal positions. All three methods show good visual quality and take only a small fraction of rendering time. This simulation runs on the GPU and works smoothly as a part of rendering pipeline. Simulating around 20,000 strands composed of total 0.22 million vertices takes less than 1 millisecond. Simulation parameters such as stiffness or number of iterations for shape constraints can be manipulated by users interactively. It helps designers choose the right parameters for various hair styles and conditions. Also the simulation can handle various situations interactively.
Efficient Cloth Simulation Using an Adaptive Finite Element Method
(The Eurographics Association, 2012) Bender, Jan; Deul, Crispin; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
In this paper we present an efficient adaptive cloth simulation based on the sqrt-3-refinement scheme. Our adaptive cloth model can handle arbitrary triangle meshes and is not restricted to regular grid meshes which are required by other methods. Previous works on adaptive cloth simulation often use discrete cloth models like mass-spring systems in combination with a specific subdivision scheme. The problem of such models is that the simulation does not converge to the correct solution as the mesh is refined. We propose to use a cloth model which is based on continuum mechanics since continuous models do not have this problem. In order to perform an efficient simulation we use a linear elasticity model in combination with a corotational formulation. The sqrt-3-subdivision scheme has the advantage that it generates high quality meshes while the number of triangles increases only by a factor of 3 in each refinement step. However, the original scheme only defines a mesh refinement. Therefore, we introduce an extension to support the coarsening of our simulation model as well. Our proposed mesh adaption can be performed efficiently and therefore does not cause much overhead. In this paper we will show that a significant performance gain can be achieved by our adaptive method.
Policies for Goal Directed Multi-Finger Manipulation
(The Eurographics Association, 2012) Andrews, Sheldon; Kry, Paul G.; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
We present a method for one-handed task based manipulation of objects. Our approach uses a mid-level multiphase approach to break the problem into three parts, providing an appropriate control strategy for each phase and resulting in cyclic finger motions that accomplish the task. All motion is physically based, and guided by a policy computed for a particular task. The exact trajectory is never specified as the goal of our different tasks are concerned with the final orientation and position of the object. The offline simulations used to learn the policy are effective solutions for the task, but an important aspect of our work is that the policy is general enough to be used online in real time. We present two manipulation tasks and discuss their performance along with limitations.
Mapping Volumetric Meshes to Point-based Motion Models
(The Eurographics Association, 2012) Jund, Thomas; Allaoui, Ali; Darles, Emmanuelle; Skapin, Xavier; Meseure, Philippe; Luciani, Annie; Jan Bender and Arjan Kuijper and Dieter W. Fellner and Eric Guerin
Particle-based models produce various, flexible and optimized animations. Intrinsically, they are neither based on a boundary representation nor on volumetric objet meshed representations. Thus, they raise rendering issues since they do not contain enough geometrical information and do not even provide an underlying spatial topology. Consequently, various geometrical shapes can be used to render a motion produced by a meshless model, leading to different visual interpretations. To our knowledge, there is no generic methods to associate any set of points in motion with a topology-based geometric model. In this paper, we propose a framework to map arbitrary volumetric meshes to arbitrary point-based motions and to control the topological changes. Therefore, from only one motion description, different visual results can be obtained. This framework breaks down into three distinct processes: a particles to vertices mapping, the definition of a motion function and the definition of topological modifications and events triggering them. We show how the manipulation of these parameters allows to experiment different mappings for a particular motion and that our framework includes most of previous known mappings.

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