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Item Linear-Time Dynamics for Multibody Systems with General Joint Models(The Eurographics Association, 2010) Si, Weiguang; Guenter, Brian; MZoran Popovic and Miguel OtaduyMost current linear-time forward dynamics algorithms support only simple types of joints due to difficulties in computing derivatives of joint transformations up to order two.We apply the D* symbolic differentiation algorithm to a recursive formulation of forward dynamics to get a highly efficient linear-time forward dynamics algorithm supporting multibody systems with general scleronomic joints. With this new algorithm we can easily build a treetopology multibody system with complex joint models and perform forward dynamics efficiently. The source code for the algorithm is freely available for non-commercial use.Item Interactive Simulation of a Continuum Mechanics based Torsional Thread(The Eurographics Association, 2010) Larsson, Karl; Wallgren, Göran; Larson, Mats G.; Kenny Erleben and Jan Bender and Matthias TeschnerThis paper introduces a continuum mechanics based thread model for use in real-time simulation. The model includes both rotary inertia, shear deformation and torsion. It is based on a three-dimensional beam model, using a corotational approach for interactive simulation speeds as well as adaptive mesh resolution to maintain accuracy. Desirable aspects of this model from a numerical and implementation point of view include a true constant and symmetric mass matrix, a symmetric and easily evaluated tangent stiffness matrix, and easy implementation of time-stepping algorithms. From a modeling perspective interesting features are deformation of the thread cross section and the use of arbitrary cross sections without performance penalty.Item Animating Non-Humanoid Characters with Human Motion Data(The Eurographics Association, 2010) Yamane, Katsu; Ariki, Yuka; Hodgins, Jessica; MZoran Popovic and Miguel OtaduyThis paper presents a method for generating animations of non-humanoid characters from human motion capture data. Characters considered in this work have proportion and/or topology significantly different from humans, but are expected to convey expressions and emotions through body language that are understandable to human viewers. Keyframing is most commonly used to animate such characters. Our method provides an alternative for animating non-humanoid characters that leverages motion data from a human subject performing in the style of the target character. The method consists of a statistical mapping function learned from a small set of corresponding key poses, and a physics-based optimization process to improve the physical realism.We demonstrate our approach on three characters and a variety of motions with emotional expressionsItem Control Systems for Human Running using an Inverted Pendulum Model and a Reference Motion Capture Sequence(The Eurographics Association, 2010) Kwon, Taesoo; Hodgins, Jessica; MZoran Popovic and Miguel OtaduyPhysical simulation is often proposed as a way to generate motion for interactive characters. A simulated character has the potential to adapt to changing terrain and disturbances in a realistic and robust manner. In this paper, we present a balancing control algorithm based on a simplified dynamic model, an inverted pendulum on a cart. The simplified model lacks the degrees of freedom found in a full human model, so we analyze a captured reference motion in a preprocessing step and use that information about human running patterns to supplement the balance algorithms provided by the inverted pendulum controller. At run-time, the controller plans a desired motion at every frame based on the current estimate of the pendulum state and a predicted pendulum trajectory. By tracking this time-varying trajectory, our controller creates a running character that dynamically balances, changes speed and makes turns. The initial controller can be optimized to further improve the motion quality with an objective function that minimizes the difference between a planned desired motion and a simulated motion. We demonstrate the power of this approach by generating running motions at a variety of speeds (3m/s to 5m/s), following a curved path, and in the presence of disturbance forces and a skipping motion.Item Shortest Paths with Arbitrary Clearance from Navigation Meshes(The Eurographics Association, 2010) Kallmann, Marcelo; MZoran Popovic and Miguel OtaduyThis paper addresses the problem of efficiently computing optimal paths of arbitrary clearance from a polygonal representation of a given virtual environment. Key to the proposed method is a new type of triangulated navigation mesh, called a Local Clearance Triangulation, which enables the efficient and correct determination if a disc of arbitrary size can pass through any narrow passages of the mesh. The proposed approach uniquely balances speed of computation and optimality of paths by first computing high-quality locally shortest paths efficiently in optimal time. Only in case global optimality is needed, an extended search will gradually improve the current path (if not already the global optimal) until the globally shortest one is determined. The presented method represents the first solution correctly extracting shortest paths of arbitrary clearance directly from a triangulated environment.