Search Results

Now showing 1 - 10 of 33
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    Environment-aware Real-Time Crowd Control
    (The Eurographics Association, 2012) Henry, Joseph; Shum, Hubert P. H.; Komura, Taku; Jehee Lee and Paul Kry
    Real-time crowd control has become an important research topic due to the recent advancement in console game quality and hardware processing capability. The degrees of freedom of a crowd is much higher than that provided by a standard user input device. As a result most crowd control systems require the user to design the crowd move- ments through multiple passes, such as first specifying the crowd's start and goal points, then providing the agent trajectories with streamlines. Such a multi-pass control would spoil the responsiveness and excitement of real- time games. In this paper, we propose a new, single-pass algorithm to control crowds using a deformable mesh. When controlling crowds, we observe that most of the low level details are related to passive interactions between the crowd and the environment, such as obstacle avoidance and diverging/merging at cross points. Therefore, we simplify the crowd control problem by representing the crowd with a deformable mesh that passively reacts to the environment. As a result, the user can focus on high level control that is more important for context delivery. Our algorithm provides an efficient crowd control framework while maintaining the quality of the simulation, which is useful for real-time applications such as strategy games.
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    Quaternion Space Sparse Decomposition for Motion Compression and Retrieval
    (The Eurographics Association, 2012) Zhu, Mingyang; Sun, Huaijiang; Deng, Zhigang; Jehee Lee and Paul Kry
    Quaternion has become one of the most widely used representations for rotational transformations in 3D graphics for decades. Due to the sparse nature of human motion in both the spatial domain and the temporal domain, an unexplored yet challenging research problem is how to directly represent intrinsically sparse human motion data in quaternion space. In this paper we propose a novel quaternion space sparse decomposition (QSSD) model that decomposes human rotational motion data into two meaningful parts (namely, the dictionary part and the weight part) with the sparseness constraint on the weight part. Specifically, a linear combination (addition) operation in Euclidean space is equivalently modeled as a quaternion multiplication operation, and the weight of linear combination is modeled as a power operation on quaternion. Besides validations of the robustness, convergence, and accuracy of the QSSD model, we also demonstrate its two selected applications: human motion data compression and content-based human motion retrieval. Through numerous experiments and quantitative comparisons, we demonstrate that the QSSD-based approaches can soundly outperform existing state-of-the-art human motion compression and retrieval approaches.
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    Linear-Time Smoke Animation with Vortex Sheet Meshes
    (The Eurographics Association, 2012) Brochu, Tyson; Keeler, Todd; Bridson, Robert; Jehee Lee and Paul Kry
    We present the first quality physics-based smoke animation method which runs in time approximately linear in the size of the rendered two-dimensional visual detail. Our fundamental representation is a closed triangle mesh surface dividing space between clear air and a uniformly smoky region, on which we compute vortex sheet dynamics to accurately solve inviscid buoyant flow. We handle arbitrary moving no-stick solid boundaries and by default handle an infinite domain. The simulation itself runs in time linear to the number of triangles thanks to the use of a well-conditioned integral equation treatment together with a Fast Multipole Method for linear-time summations, providing excellent performance. Basic zero-albedo smoke rendering, with embedded solids, is easy to implement for interactive rates, and the mesh output can also serve as an extremely compact and detailed input to more sophisticated volume rendering.
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    Smoke Sheets for Graph-Structured Vortex Filaments
    (The Eurographics Association, 2012) Barnat, Alfred; Pollard, Nancy S.; Jehee Lee and Paul Kry
    Smoke is one of the core phenomena which fluid simulation techniques in computer graphics have attempted to capture. It is both well understood mathematically and important in lending realism to computer generated effects. In an attempt to overcome the diffusion inherent to Eulerian grid-based simulators, a technique has recently been developed which represents velocity using a sparse set of vortex filaments. This has the advantage of providing an easily understandable and controllable model for fluid velocity, but is computationally expensive because each filament affects the fluid velocity over an unbounded region of the simulation space. We present an alternative to existing techniques which merge adjacent filament rings, instead allowing filaments to form arbitrary structures, and we develop a new set of reconnection criteria to take advantage of this filament graph. To complement this technique, we also introduce a method for smoke surface tracking and rendering designed to minimize the number of sample points without introducing excessive diffusion or blurring. Though this representation lends itself to straightforward real-time rendering, we also present a method which renders the thin sheets and curls of smoke as diffuse volumes using any GPU capable of supporting geometry shaders.
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    Contact-Invariant Optimization for Hand Manipulation
    (The Eurographics Association, 2012) Mordatch, Igor; Popovic, Zoran; Todorov, Emanuel; Jehee Lee and Paul Kry
    We present a method for automatic synthesis of dexterous hand movements, given only high-level goals specifying what should happen to the object being manipulated. Results are presented on a wide range of tasks including grasping and picking up objects, twirling them between the fingers, tossing and catching, drawing. This work is an extension of the recent contact-invariant optimization (CIO) method, which introduced auxiliary decision variables directly specifying when and where contacts should occur, and optimized these variables together with the movement trajectory. Our contribution here is extending the unique contact model used in CIO which was specific to locomotion tasks, as well as applying the extended method systematically to hand manipulation.
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    The Intersection Contour Minimization Method for Untangling Oriented Deformable Surfaces
    (The Eurographics Association, 2012) Ye, Juntao; Zhao, Jing; Jehee Lee and Paul Kry
    The Intersection Contour Minimization (ICM) method [VM06] has been proven to be an effective history-free algorithm for resolving collisions between non-oriented deformable surfaces. In many circumstances, however, surface orientation information are often implied in the context. Being completely blind to such information in the ICM method often leads to unexpected result: either failure or slow convergence in certain intersection config- urations. By introducing the concept of ''repulsive normal'' into ICM, many of those once-failure configurations can be resolved successfully. Even for those once-successful configurations, repulsive normals usually speed-up the convergence. Moreover, the ICM method that was originally designed for polygonal meshes can actually be adapted to resolve collisions between a polygon mesh and an analytical surface. This paper presents one such extension collisions between a polygon mesh and a capsule.
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    Evaluating the Plausibility of Edited Throwing Animations
    (The Eurographics Association, 2012) Vicovaro, Michele; Hoyet, Ludovic; Burigana, Luigi; O'Sullivan, Carol; Jehee Lee and Paul Kry
    Animation budget constraints during the development of a game often call for the use of a limited set of generic motions. Editing operations are thus generally required to animate virtual characters with a sufficient level of variety. Evaluating the perceptual plausibility of edited animations can therefore contribute greatly towards producing visually plausible animations. In this paper we study observers' sensitivity to manipulations of overarm and underarm biological throwing animations. In our first experiment, we used Dynamic Time Warping to edit the biological throwing motions, and modified the release velocity of the ball accordingly. We found that observers are more tolerant to speeding up of the original throwing motion than to slowing down, and that slowed down underarm throws are perceived as particularly unnatural. In our second experiment, we modified separately horizontal and vertical components of the release velocity of the ball, while leaving the motion of the thrower unchanged. We found that observers are more sensitive to manipulations of the horizontal component in overarm throws, and of the vertical component in underarm throws. As in the first experiment, we found that observers are most disturbed by decreases in the velocity of the ball in underarm throws. Our results provide valuable insights for developers of games and VR applications by specifying thresholds for the perceptual plausibility of throwing manipulations.
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    Real-time Particle Fluid Simulation with WCSPH
    (The Eurographics Association, 2012) Zhang, Fengquan; Shen, Xukun; Long, Xiang; Zhao, Bin; Hu, Lei; Chris Bregler and Pedro Sander and Michael Wimmer
    In this paper, based on weakly compressible smoothed particles hydrodynamics (WCSPH), we present a method for simulating high quality fluid. We propose a new pressure equation to reduce time overhead, speed up convergence towards small density fluctuations and allow for a larger time step than that of traditional approaches. And based on the new equation, we introduce a new adaptive time-stepping approach that automatically adapts the time step according to each particle current individual time step, thus improving the efficiency of computation and contributing much to a real-time particle fluid simulation. For real-time simulation, we make full use of CPU and GPU in a combined way to build a parallel platform, namely Multi-GPU platform. And optimization of the platform design is made to run a simulation with realistic visual effects in real time.
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    Controlling Liquids Using Meshes
    (The Eurographics Association, 2012) Raveendran, Karthik; Thuerey, Nils; Wojtan, Chris; Turk, Greg; Jehee Lee and Paul Kry
    We present an approach for artist-directed animation of liquids using multiple levels of control over the simulation, ranging from the overall tracking of desired shapes to highly detailed secondary effects such as dripping streams, separating sheets of fluid, surface waves and ripples. The first portion of our technique is a volume preserving morph that allows the animator to produce a plausible fluid-like motion from a sparse set of control meshes. By rasterizing the resulting control meshes onto the simulation grid, the mesh velocities act as boundary conditions during the projection step of the fluid simulation. We can then blend this motion together with uncontrolled fluid velocities to achieve a more relaxed control over the fluid that captures natural inertial effects. Our method can produce highly detailed liquid surfaces with control over sub-grid details by using a mesh-based surface tracker on top of a coarse grid-based fluid simulation. We can create ripples and waves on the fluid surface attracting the surface mesh to the control mesh with spring-like forces and also by running a wave simulation over the surface mesh. Our video results demonstrate how our control scheme can be used to create animated characters and shapes that are made of water.
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    Real-Time Example-Based Elastic Deformation
    (The Eurographics Association, 2012) Koyama, Yuki; Takayama, Kenshi; Umetani, Nobuyuki; Igarashi, Takeo; Jehee Lee and Paul Kry
    We present an example-based elastic deformation method that runs in real time. Example-based elastic deformation was originally presented by Martin et al. [MTGG11], where an artist can intuitively control elastic material behaviors by simply giving example poses. Their FEM-based approach is, however, computationally expensive requiring nonlinear optimization, which hinders its use in real-time applications such as games. Our contribution is to formulate an analogous concept using the shape matching framework, which is fast, robust, and easy to implement. The key observation is that each overlapping local region's right stretch tensor obtained by polar decomposition is a natural choice for a deformation descriptor. This descriptor allows us to represent the pose space as a linear blending of examples. At each time step, the current deformation descriptor is linearly projected onto the example manifold, and then used to modify the rest shape of each local region when computing goal positions. Our approach is two orders of magnitude faster than Martin et al.'s approach while producing comparable example-based elastic deformations.