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Item Multi-Domain Real-time Planning in Dynamic Environments(ACM SIGGRAPH / Eurographics Association, 2013) Kapadia, Mubbasir; Beacco, Alejandro; Garcia, Francisco; Reddy, Vivek; Pelechano, Nuria; Badler, Norman I.; Theodore Kim and Robert SumnerThis paper presents a real-time planning framework for multicharacter navigation that enables the use of multiple heterogeneous problem domains of differing complexities for navigation in large, complex, dynamic virtual environments. The original navigation problem is decomposed into a set of smaller problems that are distributed across planning tasks working in these different domains. An anytime dynamic planner is used to efficiently compute and repair plans for each of these tasks, while using plans in one domain to focus and accelerate searches in more complex domains. We demonstrate the benefits of our framework by solving many challenging multi-agent scenarios in complex dynamic environments requiring space-time precision and explicit coordination between interacting agents, by accounting for dynamic information at all stages of the decision-making process.Item RTSG: Ray Tracing for X3D via a Flexible Rendering Framework(The Eurographics Association, 2009) Rubinstein, Dmitri; Georgiev, Iliyan; Schug, Benjamin; Slusallek, Philipp; Dieter W. Fellner and Alexei Sourin and Johannes Behr and Krzysztof WalczakVRML and X3D are the most widely adopted standards for interactive 3D content interchange. However, they are both designed around the common restricted functionality available in hardware graphics processors. Thus, most existing scene graph implementations are tightly integrated with rasterization APIs, which have difficulties simulating advanced global lighting effects. Conversely, complex photo-realistic effects are naturally supported by ray tracing based rendering algorithms [Glassner 1989]. Due to recent research advances and the constantly increasing computing power of commodity PCs, ray tracing is emerging as an interesting alternative for interactive applications. In this paper we present RTSG (Real-Time Scene Graph), a flexible scene management and rendering system. RTSG is X3D-compliant and has been designed to efficiently support both ray tracing and rasterization using a backend-independent rendering infrastructure. We describe two ray tracing and one rasterization backends and demonstrate that they achieve real-time rendering performance.Item Differential Blending for Expressive Sketch-Based Posing(ACM SIGGRAPH / Eurographics Association, 2013) Öztireli, A. Cengiz; Baran, Ilya; Popa, Tiberiu; Dalstein, Boris; Sumner, Robert W.; Gross, Markus; Theodore Kim and Robert SumnerGenerating highly expressive and caricatured poses can be difficult in 3D computer animation because artists must interact with characters indirectly through complex character rigs. Furthermore, since caricatured poses often involve large bends and twists, artifacts arise with traditional skinning algorithms that are not designed to blend large, disparate rotations and cannot represent extremely large rotations. To overcome these problems, we introduce a differential blending algorithm that can successfully encode and blend large transformations, overcoming the inherent limitation of previous skeletal representations. Based on this blending method, we illustrate a sketch-based interface that supports curved bones and implements the line-of-action concept from hand-drawn animation to create expressive poses in 3D animation. By interpolating stored differential transformations across temporal keyframes, our system also generates caricatured animation. We present a detailed technical analysis of our differential blending algorithm and show several posing and animation results created using our system to demonstrate the utility of our method in practice.Item Relationship Descriptors for Interactive Motion Adaptation(ACM SIGGRAPH / Eurographics Association, 2013) Al-Asqhar, Rami Ali; Komura, Taku; Choi, Myung Geol; Theodore Kim and Robert SumnerThis paper presents an interactive motion adaptation scheme for close interactions between skeletal characters and mesh structures, such as moving through restricted environments, and manipulating objects. This is achieved through a new spatial relationship-based representation, which describes the kinematics of the body parts by the weighted sum of translation vectors relative to points selectively sampled over the surfaces of the mesh structures. In contrast to previous discrete representations that either only handle static spatial relationships, or require offline, costly optimization processes, our continuous framework smoothly adapts the motion of a character to large updates of the mesh structures and character morphologies on-the-fly, while preserving the original context of the scene. The experimental results show that our method can be used for a wide range of applications, including motion retargeting, interactive character control and deformation transfer for scenes that involve close interactions. Our framework is useful for artists who need to design animated scenes interactively, and modern computer games that allow users to design their own characters, objects and environments.Item LandSketch: A First Person Point-of-View Example-Based Terrain Modeling Approach(ACM, 2013) Passos, Vladimir Alves dos; Igarashi, Takeo; Levent Burak Kara and Cindy GrimmWe present an intuitive interface for easy modeling of terrains, compatible with example-based synthesis approach. The interface consists on a picture's canvas-like screen, where the user sketches silhouettes of mountains, as he would do if drawing mountains on a piece of paper. Realistic results are achieved by combining copies of the example terrain in such a manner that matches the sketched silhouette. We use Digital Elevation Models (DEM) of real world terrains as source data, and a weighted sum function to continually combine the heights.Item Efficient Divide-And-Conquer Ray Tracing using Ray Sampling(ACM, 2013) Nabata, Kosuke; Iwasaki, Kei; Dobashi, Yoshinori; Nishita, Tomoyuki; Kayvon Fatahalian and Christian TheobaltDivide-and-conquer ray tracing (DACRT) methods solve intersection problems between large numbers of rays and primitives by recursively subdividing the problem size until it can be easily solved. Previous DACRT methods subdivide the intersection problem based on the distribution of primitives only, and do not exploit the distribution of rays, which results in a decrease of the rendering performance especially for high resolution images with antialiasing. We propose an efficient DACRT method that exploits the distribution of rays by sampling the rays to construct an acceleration data structure. To accelerate ray traversals, we have derived a new cost metric which is used to avoid inefficient subdivision of the intersection problem where the number of rays is not sufficiently reduced. Our method accelerates the tracing of many types of rays (primary rays, less coherent secondary rays, random rays for path tracing) by a factor of up to 2 using ray sampling.Item Velocity-Based Modeling of Physical Interactions in Multi-Agent Simulations(ACM SIGGRAPH / Eurographics Association, 2013) Kim, Sujeong; Guy, Stephen J.; Manocha, Dinesh; Theodore Kim and Robert SumnerWe present an interactive algorithm to model physics-based interactions in multi-agent simulations. Our approach is capable of modeling both physical forces and interactions between agents and obstacles, while allowing the agents to anticipate and avoid collisions for local navigation. We combine velocity-based collision-avoidance algorithms with external physical forces. The overall formulation can approximately simulate various physical e?ects, including collisions, pushing, deceleration and resistive forces. We have integrated our approach with an open-source physics engine and use the resulting system to model plausible behaviors of and interactions among large numbers of agents in dense environments. Our algorithm can simulate a few thousand agents at interactive rates and can generate many emergent behaviors. The overall approach is useful for interactive applications that require plausible physical behavior, including games and virtual worlds.Item Consistent Surface Model for SPH-based Fluid Transport(ACM SIGGRAPH / Eurographics Association, 2013) Orthmann, Jens; Hochstetter, Hendrik; Bader, Julian; Bayraktar, Serkan; Kolb, Andreas; Theodore Kim and Robert SumnerSurface effects play an essential role in fluid simulations. A vast number of dynamics including wetting of surfaces, cleansing, and foam dynamics are based on surface-surface and surface-bulk interactions, which in turn rely on a robust surface computation. In this paper we introduce a conservative Lagrangian formulation of surface effects based upon incompressible smoothed particle hydrodynamics (SPH). The key concept of our approach is to realize an implicit definition of the fluid's (free) surface by assigning each particle a value estimating its surface area. Based on this consistent surface representation, a conservative coupling of bulk and surface is achieved. We demonstrate the applicability and robustness of our approach for several types of surface-relevant effects including adsorption, diffusion and reaction kinetics.Item Chemical Education using Feelable Molecules(The Eurographics Association, 2009) Davies, R. Andrew; Maskery, James S.; John, Nigel W.; Dieter W. Fellner and Alexei Sourin and Johannes Behr and Krzysztof WalczakTwo different approaches for the preparation of novel cost-effective molecular haptic applications (Figure 1) are described. The former utilises Perl scripting within a commercial molecular modelling package to generate static / animated H3D scene graphs for haptic CPK space-filling atomic perception. Within the second approach, key chemical concepts such as reactivity, aciditity and periodicity can be investigated using prototype H3D user interfaces.Item A Circle-based Vectorization Algorithm for Drawings with Shadows(ACM, 2013) Bonnici, Alexandra; Camilleri, Kenneth; Levent Burak Kara and Cindy GrimmVectorization algorithms described in the literature assume that the drawings being vectorized are either binary images or have a clear white background. Sketches of artistic objects however also contain shadows which help the artist to portray intent, particularly in potentially ambiguous sketches. Such sketches are difficult to binarise since the shading strokes make these sketches non bimodal. For this reason, we describe a circle-based vectorization algorithm that uses signatures obtained from sample points on the line strokes to identify and vectorize the line strokes in the sketch. We show that the proposed algorithm performs as well as other vectorization techniques described in the literature, despite the shadows present in the sketch.