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Fast and Controllable Simulation of the Shattering of Brittle ObjectsJeffrey Smith, Andrew Witkin, and David Baraff AbstractWe present a method for the rapid and controllable simulation of the shattering of brittle objects under impact. An object is represented as a set of point masses connected by distance-preserving linear constraints. This use of constraints, rather than stiff springs, gains us a significant advantage in speed while still retaining fine control over the fracturing behavior. The forces exerted by these constraints during impact are computed using Lagrange multipliers. These constraint forces are then used to determine when and where the object will break, and to calculate the velocities of the newly created fragments. We present the details of our technique together with examples illustrating its use. CitationJeffrey Smith, Andrew Witkin, and David Baraff. Fast and controllable simulation of the shattering of brittle objects. Computer Graphics Forum, 20(2):81–91, 2001. [BiBTeX] Animating Athletic Motion Planning By ExampleRonald Metoyer and Jessica K. Hodgins CitationRonald Metoyer and Jessica K. Hodgins. Animating athletic motion planning by example. In Graphics Interface, pages 61–68, 2000. [BiBTeX] Links
Automatic Joint Parameter Estimation from Magnetic Motion Capture DataJames F. O'Brien, Robert Bodenheimer, Gabriel Brostow, and Jessica K. Hodgins CitationJames F. O'Brien, Robert Bodenheimer, Gabriel Brostow, and Jessica K. Hodgins. Automatic joint parameter estimation from magnetic motion capture data. In Graphics Interface, pages 53–60, 2000. [BiBTeX] LinksCombining Active and Passive Simulations for Secondary MotionJames F. O'Brien, Victor B. Zordan, and Jessica K. Hodgins AbstractObjects that move in response to the actions of a main character often make an important contribution to the visual richness of an animated scene. We use the term "secondary motion" to refer to passive motions generated in response to the movements of characters and other objects or environmental forces. Secondary motions aren't normally the mail focus of an animated scene, yet their absence can distract or disturb the viewer, destroying the illusion of reality created by the scene. We describe how to generate secondary motion by coupling physically based simulations of passive objects to actively controlled characters. CitationJames F. O'Brien, Victor B. Zordan, and Jessica K. Hodgins. Combining active and passive simulations for secondary motion. IEEE Computer Graphics & Applications, 20(4):86–96, August 2000. [BiBTeX] Links
Animating ExplosionsGary D. Yngve, James F. O'Brien, and Jessica K. Hodgins AbstractIn this paper, we introduce techniques for animating explosions and their effects. The primary effect of an explosion is a disturbance that causes a shock wave to propagate through the surrounding medium. The disturbance determines the behavior of nearly all other secondary effects seen in explosion. We simulate the propagation of an explosion through the surrounding air using a computational fluid dynamics model based on the equations for compressible, viscous flow. To model the numerically stable formation of shocks along blast wave fronts, we employ an integration method that can handle steep pressure gradients without introducing inappropriate damping. The system includes two-way coupling between solid objects and surrounding fluid. Using this technique, we can generate a variety of effects including shaped explosive charges, a projectile propelled from a chamber by an explosion, and objects damaged by a blast. With appropriate rendering techniques, our explosion model can be used to create such visual effects as fireballs, dust clouds, and the refraction of light caused by a blast wave. CitationGary D. Yngve, James F. O'Brien, and Jessica K. Hodgins. Animating explosions. In Proceedings of ACM SIGGRAPH 2000, pages 29–36, July 2000. [BiBTeX] Links
Animating FractureJames F. O'Brien and Jessica K. Hodgins CitationJames F. O'Brien and Jessica K. Hodgins. Animating fracture. Communications of the ACM, 43(7):68–75, 2000. [BiBTeX] LinksInteractive Manipulation of Rigid Body SimulationsJovan Popović, Steven M. Seitz, Michael Erdmann, Zoran Popović, and Andrew Witkin AbstractPhysical simulation of dynamic objects has become commonplace in computer graphics because it produces highly realistic animations. In this paradigm the animator provides few physical parameters such as the objects' initial positions and velocities, and the simulator automatically generates realistic motions. The resulting motion, however, is difficult to control because even a small adjustment of the input parameters can drastically affect the subsequent motion. Furthermore, the animator often wishes to change the end-result of the motion instead of the initial physical parameters. We describe a novel interactive technique for intuitive manipulation of rigid multi-body simulations. Using our system, the animator can select bodies at any time and simply drag them to desired locations. In response, the system computes the required physical parameters and simulates the resulting motion. Surface characteristics such as normals and elasticity coefficients can also be automatically adjusted to provide a greater range of feasible motions, if the animator so desires. Because the entire simulation editing process runs at interactive speeds, the animator can rapidly design complex physical animations that would be difficult to achieve with existing rigid body simulators. CitationJovan Popović, Steven M. Seitz, Michael Erdmann, Zoran Popović, and Andrew Witkin. Interactive manipulation of rigid body simulations. In Proceedings of SIGGRAPH 2000, pages 209–218, July 2000. [BiBTeX] LinksTangible Interaction + Graphical Interpretation: a New Approach to 3D ModelingDavid Anderson, James L. Frankel, Joe Marks, Aseem Agarwala, Paul Beardsley, Jessica K. Hodgins, Darren Leigh, Kathy Ryall, Eddie Sullivan, and Jonathan S. Yedidia AbstractConstruction toys are a superb medium for geometric models. We argue that such toys, suitably instrumented or sensed, could be the inspiration for a new generation of easy-to-use, tangible modeling systems.especially if the tangible modeling is combined with graphical-interpretation techniques for enhancing nascent models automatically. The three key technologies needed to realize this idea are embedded computation, vision-based acquisition, and graphical interpretation. We sample these technologies in the context of two novel modeling systems: physical building blocks that self-describe, interpret, and decorate the structures into which they are assembled; and a system for scanning, interpreting, and animating clay figures. CitationDavid Anderson, James L. Frankel, Joe Marks, Aseem Agarwala, Paul Beardsley, Jessica K. Hodgins, Darren Leigh, Kathy Ryall, Eddie Sullivan, and Jonathan S. Yedidia. Tangible interaction + graphical interpretation: a new approach to 3d modeling. In Proceedings of ACM SIGGRAPH 2000, pages 393–402, July 2000. [BiBTeX] The Effects of Noise on the Perception of Animated Human RunningBobby Bodenheimer, Anna V. Shleyfman, and Jessica K. Hodgins CitationBobby Bodenheimer, Anna V. Shleyfman, and Jessica K. Hodgins. The effects of noise on the perception of animated human running. In Computer Animation and Simulation '99, September 1999. [BiBTeX] Links
Tracking and Modifying Upper-Body Human Motion Data with Dynamic SimulationVictor B. Zordan and Jessica K. Hodgins CitationVictor B. Zordan and Jessica K. Hodgins. Tracking and modifying upper-body human motion data with dynamic simulation. In Computer Animation and Simulation '99, September 1999. [BiBTeX] Links
Graphical Modeling and Animation of Brittle FractureJames F. O'Brien and Jessica K. Hodgins AbstractIn this paper, we augment existing techniques for simulating flexible objects to include models for crack initiation and propagation in three-dimensional volumes. By analyzing the stress tensors computed over a finite element model, the simulation determines where cracks should initiate and in what directions they should propagate. We demonstrate our results with animations of breaking bowls, cracking walls, and objects that fracture when they collide. By varying the shape of the objects, the material properties, and the initial conditions of the simulations, we can create strikingly different effects ranging from a wall that shatters when it is hit by a wrecking ball to a bowl that breaks in two when it is dropped on edge. CitationJames F. O'Brien and Jessica K. Hodgins. Graphical modeling and animation of brittle fracture. In Proceedings of SIGGRAPH 99, pages 137–146, August 1999. [BiBTeX] LinksFast Synthetic Vision, Memory, and Learning Models for Virtual HumansJames J. Kuffner and Jean-Claude Latombe AbstractThe paper presents a simple and efficient method of modeling synthetic vision, memory, and learning for autonomous animated characters in real time virtual environments. The model is efficient in terms of both storage requirements and update times, and can be flexibly combined with a variety of higher level reasoning modules or complex memory rules. The design is inspired by research in motion planning, control, and sensing for autonomous mobile robots. We apply this framework to the problem of quickly synthesizing from navigation goals the collision-free motions for animated human figures in changing virtual environments. We combine a low level path planner, a path following controller and cyclic motion capture data to generate the underlying animation. Graphics rendering hardware is used to simulate the visual perception of a character, providing a feedback loop to the overall navigation strategy. The synthetic vision and memory update rules can handle dynamic environments where objects appear, disappear, or move around unpredictably. The resulting model is suitable for a variety of real time applications involving autonomous animated characters. CitationJames J. Kuffner and Jean-Claude Latombe. Fast synthetic vision, memory, and learning models for virtual humans. In Proceedings of Computer Animation 1999, pages 118–127, May 1999. [BiBTeX] Animating Sand, Mud, and SnowRobert Sumner, James F. O'Brien, and Jessica K. Hodgins CitationRobert Sumner, James F. O'Brien, and Jessica K. Hodgins. Animating sand, mud, and snow. Computer Graphics Forum, 18(1):17–26, March 1999. [BiBTeX] Links
Two methods for display of high contrast imagesJack Tumblin, Jessica K. Hodgins, and Brian K. Guenter AbstractHigh contrast images are common in night scenes and other scenes that include dark shadows and bright light sources. These scenes are difficult to display because their contrasts greatly exceed the range of most display devices for images. As a result, the image constrasts are compressed or truncated, obscuring subtle textures and details. Humans view and understand high contrast scenes easily, "adapting" their visual response to avoid compression or truncation with no apparent loss of detail. By imitating some of these visual adaptation processes, we developed methods for the improved display of high-contrast images. The first builds a display image from several layers of lighting and surface properties. Only the lighting layers are compressed, drastically reducing contrast while preserving much of the image detail. This method is practical only for synthetic images where the layers can be retained from the rendering process. The second method interactively adjusts the displayed image to preserve local contrasts in a small "foveal" neighborhood. Unlike the first method, this technique is usable on any image and includes a new tone reproduction operator. Both methods use a sigmoid function for contrast compression. This function has no effect when applied to small signals but compresses large signals to fit within an asymptotic limit. We demonstrate the effectiveness of these approaches by comparing processed and unprocessed images. CitationJack Tumblin, Jessica K. Hodgins, and Brian K. Guenter. Two methods for display of high contrast images. ACM Transactions on Graphics, 18(1):56–94, January 1999. [BiBTeX] LinksDynamically Simulated Characters in Virtual EnvironmentsDavid C. Brogan, Ronald A. Metoyer, and Jessica K. Hodgins CitationDavid C. Brogan, Ronald A. Metoyer, and Jessica K. Hodgins. Dynamically simulated characters in virtual environments. IEEE Computer Graphics & Applications, 18(5):58–69, September 1998. [BiBTeX] LinksLarge Steps in Cloth SimulationDavid Baraff and Andrew P. Witkin AbstractThe bottle-neck in most cloth simulation systems is that time steps must be small to avoid numerical instability. This paper describes a cloth simulation system that can stably take large time steps. The simulation systemcouples a new technique for enforcing constraints on individual cloth particles with an implicit integration method. The simulator models cloth as a triangular mesh, with internal cloth forces derived using a simple continuum formulation that supports modeling operations such as local anisotropic stretch or compression; a unified treatment of damping forces is included as well. The implicit integration method generates a large, unbanded sparse linear system at each time step which is solved using a modified conjugate gradient method that simultaneously enforces particles' constraints. The constraints are always maintained exactly, independent of the number of conjugate gradient iterations, which is typically small. The resulting simulation system is significantly faster than previous accounts of cloth simulation systems in the literature. CitationDavid Baraff and Andrew P. Witkin. Large steps in cloth simulation. In Proceedings of SIGGRAPH 98, Computer Graphics Proceedings, Annual Conference Series, pages 43–54, July 1998. [BiBTeX] Links
Adapting Simulated Behaviors For New CharactersJessica K. Hodgins and Nancy S. Pollard AbstractThis paper describes an algorithm for automatically adapting existing simulated behaviors to new characters. Animating a new character is difficult because a control system tuned for one character will not, in general,work on a characterwith different limb lengths, masses, or moments of inertia. The algorithm presented here adapts the control system to a new character in two stages. First, the control system parameters are scaled based on the sizes, masses, and moments of inertia of the new and the original characters. Then a subset of the parameters is fine-tuned using a search process based on simulated annealing. To demonstrate the effectiveness of this approach, we animate the running motion of a woman, child, and imaginary character bymodifying the control systemfor a man. We also animate the bicycling motion of a second imaginary character by modifying the control system for a man. We evaluate the results of this approach by comparing the motion of the simulated human runnerswith video of an actual child andwith data for men,women, and children in the literature. In addition to adapting a control system for a new model, this approach can also be used to adapt the control system in an on-line fashion to produce a physically realistic metamorphosis from the original to the new model while the morphing character is performing the behavior. We demonstrate this on-line adaptation with a morph from a man to a woman over a period of twenty seconds. CitationJessica K. Hodgins and Nancy S. Pollard. Adapting simulated behaviors for new characters. In Proceedings of SIGGRAPH 97, pages 153–162, August 1997. [BiBTeX] Transitions Between Dynamically Simulated Motions: Leaping, Tumbling, Landing, and BalancingWayne L. Wooten and Jessica K. Hodgins CitationWayne L. Wooten and Jessica K. Hodgins. Transitions between dynamically simulated motions: Leaping, tumbling, landing, and balancing. In ACM SIGGRAPH 97 Visual Proceedings: The art and interdisciplinary programs of SIGGRAPH '97, page 217. ACM Press, 1997. [BiBTeX] Linear-Time Dynamics using Lagrange MultipliersAbstractCurrent linear-time simulation methods for articulated figures are based exclusively on reduced-coordinate formulations. This paper describes a general, non-iterative linear-time simulation method based instead on Lagrange multipliers. Lagrange multiplier methods are important for computer graphics applications because they bypass the difficult (and often intractable) problem of parameterizing a system's degrees of freedom. Given a loop-free set of n equality constraints acting between pairs of bodies, the method takes O(n) time to compute the system's dynamics. The method does not rely on matrix bandwidth, so no assumptions about the constraints' topology are needed. Bodies need not be rigid, constraints can be of various dimensions, and unlike reduced-coordinate approaches, nonholonomic (for example, velocity-dependent) constraints are allowed. An additional set of k one-dimensional constraints which induce loops and/or handle inequalities can be accommodated with cost O(kn). This makes it practical to simulate complicated, closed-loop articulated figures with joint-limits and contact at interactive rates. A complete description of a sample implementation is provided in pseudocode. CitationDavid Baraff. Linear-time dynamics using lagrange multipliers. In Proceedings of SIGGRAPH 96, Computer Graphics Proceedings, Annual Conference Series, pages 137–146, August 1996. [BiBTeX] Links
Atlanta in MotionCitationJessica K. Hodgins. Atlanta in motion. In ACM SIGGRAPH 96 Visual Proceedings: The art and interdisciplinary programs of SIGGRAPH '96, page 163. ACM Press, 1996. [BiBTeX] Animating Human AthleticsJessica K. Hodgins, Wayne L. Wooten, David C. Brogan, and James F. O'Brien AbstractThis paper describes algorithms for the animation of men and women performing three dynamic athletic behaviors: running, bicycling, and vaulting. We animate these behaviors using control algorithms that cause a physically realistic model to perform the desired maneuver. For example, control algorithms allow the simulated humans to maintain balance while moving their arms, to run or bicycle at a variety of speeds, and to perform a handspring vault. Algorithms for group behaviors allow a number of simulated bicyclists to ride as a group while avoiding simple patterns of obstacles. We add secondary motion to the animations with springmass simulations of clothing driven by the rigid-body motion of the simulated human. For each simulation, we compare the computed motion to that of humans performing similar maneuvers both qualitatively through the comparison of real and simulated video images and quantitatively through the comparison of simulated and biomechanical data. CitationJessica K. Hodgins, Wayne L. Wooten, David C. Brogan, and James F. O'Brien. Animating human athletics. In Proceedings of SIGGRAPH 95, pages 71–78, August 1995. [BiBTeX] LinksPlanning Motions with IntentionsYoshihito Koga, Koichi Kondo, James J. Kuffner, and Jean-Claude Latombe AbstractWe apply manipulation planning to computer animation. A new path planner is presented that automatically computes the collision-free trajectories for several cooperating arms to manipulate a movable object between two configurations. This implemented planner is capable of dealing with complicated tasks where regrasping is involved. In addition, we present a new inverse kinematics algorithm for the human arms. This algorithm is utilized by the planner for the generation of realistic human arm motions as they manipulate objects. We view our system as a tool for facilitating the production of animation. CitationYoshihito Koga, Koichi Kondo, James J. Kuffner, and Jean-Claude Latombe. Planning motions with intentions. In Proceedings of SIGGRAPH 94, pages 395–408, July 1994. [BiBTeX] Links
Animation of Dynamic Legged LocomotionMarc H. Raibert and Jessica K. Hodgins AbstractThis paper is about the use of control algorithms to animate dynamic legged locomotion. Control could free the animator from specifying the details of joint and limb motion while producing both physically realistic and natural looking results. We implemented computer animations of a biped robot, a quadruped robot, and a kangaroo. Each creature was modeled as a linked set of rigid bodies with compliant actuators at its joints. Control algorithms regulated the running speed, organized use of the legs, and maintained balance. All motions were generated by numerically integrating equations of motion derived from the physical models. The resulting behavior included running at various speeds, traveling with several gaits (run, trot, bound, gallop, and hop), jumping, and traversing simple paths. Whereas the use of control permitted a variety of physically realistic animated behavior to be generated with limited human intervention, the process of designing the control algorithms was not automated: the algorithms were "tweaked" and adjusted for each new creature. CitationMarc H. Raibert and Jessica K. Hodgins. Animation of dynamic legged locomotion. In Computer Graphics (Proceedings of SIGGRAPH 91), volume 25, pages 349–358, July 1991. [BiBTeX] |