SCA 09: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/427

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Anisotropic Friction for Deformable Surfaces and Solids
(ACM SIGGRAPH / Eurographics Association, 2009) Pabst, Simon; Thomaszewski, Bernhard; Straßer, Wolfgang; Eitan Grinspun and Jessica Hodgins
This paper presents a method for simulating anisotropic friction for deforming surfaces and solids. Frictional contact is a complex phenomenon that fuels research in mechanical engineering, computational contact mechanics, composite material design and rigid body dynamics, to name just a few. Many real-world materials have anisotropic surface properties. As an example, most textiles exhibit direction-dependent frictional behavior, but despite its tremendous impact on visual appearance, only simple isotropic models have been considered for cloth and solid simulation so far. In this work, we propose a simple, application-oriented but physically sound model that extends existing methods to account for anisotropic friction. The sliding properties of surfaces are encoded in friction tensors, which allows us to model frictional resistance freely along arbitrary directions. We also consider heterogeneous and asymmetric surface roughness and demonstrate the increased simulation quality on a number of two- and three-dimensional examples. Our method is computationally efficient and can easily be integrated into existing systems.
Fitting Behaviors to Pedestrian Simulations
(ACM SIGGRAPH / Eurographics Association, 2009) Lerner, Alon; Fitusi, Eitan; Chrysanthou, Yiorgos; Cohen-Or, Daniel; Eitan Grinspun and Jessica Hodgins
In this paper we present a data-driven approach for fitting behaviors to simulated pedestrian crowds. Our method annotates agent trajectories, generated by any crowd simulator, with action-tags. The aggregate effect of animating the agents according to the tagged trajectories enhances the impression that the agents are interacting with one another and with the environment. In a preprocessing stage, the stimuli which motivated a person to perform an action, as observed in a crowd video, are encoded into examples. Using the examples, non-linear, action specific influence functions are encoded into two-dimensional maps which evaluate, for each action, the relative importance of a stimulus within a configuration. At run time, given an agents stimuli configuration, the importance of each stimulus is determined and compared to the examples. Thus, the probability of performing each action is approximated and an action-tag is chosen accordingly. We fit behaviors to pedestrian crowds, thereby enhancing their natural appearance.
Guiding of Smoke Animations Through Variational Coupling of Simulations at Different Resolutions
(ACM SIGGRAPH / Eurographics Association, 2009) Nielsen, Michael B.; Christensen, Brian B.; Zafar, Nafees Bin; Roble, Doug; Museth, Ken; Eitan Grinspun and Jessica Hodgins
We propose a novel approach to guiding of Eulerian-based smoke animations through coupling of simulations at different grid resolutions. Specifically we present a variational formulation that allows smoke animations to adopt the low-frequency features from a lower resolution simulation (or non-physical synthesis), while simultaneously developing higher frequencies. The overall motivation for this work is to address the fact that art-direction of smoke animations is notoriously tedious. Particularly a change in grid resolution can result in dramatic changes in the behavior of smoke animations, and existing methods for guiding either significantly lack high frequency detail or may result in undesired features developing over time. Provided that the bulk movement can be represented satisfactorily at low resolution, our technique effectively allows artists to prototype simulations at low resolution (where computations are fast) and subsequently add extra details without altering the overall look and feel . Our implementation is based on a customized multi-grid solver with memory-efficient data structures.
Interactive Synthesis of Human-Object Interaction
(ACM SIGGRAPH / Eurographics Association, 2009) Jain, Sumit; Liu, C. Karen; Eitan Grinspun and Jessica Hodgins
We present an interactive motion editing tool for creating dynamic scenes with human and object interaction. Our approach solves for an optimal control problem that leverages methods for physics-based rigid body control and kinematics-based human motion editing. Because the humans and the objects are coupled via physical contacts, our interface allows the animator to directly change the trajectories of humans or objects and simultaneously ren- der the effect of the edits on the entire scene. Consequently, the animator can efficiently create complex interaction that requires precise synchronization, such as juggling. Our framework is generic to the choice of human motion editing method, as long as the differential information of the motion can be computed.
Pose-Timeline for Propagating Motion Edits
(ACM SIGGRAPH / Eurographics Association, 2009) Mukai, Tomohiko; Kuriyama, Shigeru; Eitan Grinspun and Jessica Hodgins
Motion editing often requires repetitive operations for modifying similar action units to give a similar effect or impression. This paper proposes a system for efficiently and flexibly editing the sequence of iterative actions by a few intuitive operations. Our system visualizes a motion sequence on a summary timeline with editable pose-icons, and drag-and-drop operations on the timeline enable intuitive controls of temporal properties of the motion such as timing, duration, and coordination. This graphical interface is also suited to transfer kinematical and temporal features between two motions through simple interactions with a quick preview of the resulting poses. Our method also integrates the concept of edit propagation by which the manual modification of one action unit is automatically transferred to the other units that are robustly detected by similarity search technique. We demonstrate the efficiency of our pose-timeline interface with a propagation mechanism for the timing adjustment of mutual actions and for motion synchronization with a music sequence.
Real-Time Deformation and Fracture in a Game Environment
(ACM SIGGRAPH / Eurographics Association, 2009) Parker, Eric G.; O'Brien, James F.; Eitan Grinspun and Jessica Hodgins
This paper describes a simulation system that has been developed to model the deformation and fracture of solid objects in a real-time gaming context. Based around a corotational tetrahedral finite element method, this system has been constructed from components published in the graphics and computational physics literatures. The goal of this paper is to describe how these components can be combined to produce an engine that is robust to unpredictable user interactions, fast enough to model reasonable scenarios at real-time speeds, suitable for use in the design of a game level, and with appropriate controls allowing content creators to match artistic direction. Details concerning parallel implementation, solver design, rendering method, and other aspects of the simulation are elucidated with the intent of providing a guide to others wishing to implement similar systems. Examples from in-game scenes captured on the Xbox 360, PS3, and PC platforms are included.
Statistical Simulation of Rigid Bodies
(ACM SIGGRAPH / Eurographics Association, 2009) Hsu, Shu-Wei; Keyser, John; Eitan Grinspun and Jessica Hodgins
We describe a method for replacing certain stages of rigid body simulation with a statistically-based approximation. We begin by collecting statistical data regarding changes in linear and angular momentum for collisions of a given object. From this data we extract a statistical "signature" for the object, giving a compact representation of the object's response to collision events. During object simulation, both the collision detection and the collision response calculations are replaced by simpler calculations based on the statistical signature. Using this approach, we are able to achieve significant improvement in the performance of rigid body simulation. The statistical behavior of the simulation is maintained, including achieving valid resting positions. We present results from a variety of simulations that demonstrate the method and its performance improvement. The method is appropriate for rigid body simulation situations requiring significant performance improvement, and allowing for some loss in fidelity.
Style Learning and Transferring for Facial Animation Editing
(ACM SIGGRAPH / Eurographics Association, 2009) Ma, Xiaohan; Le, Binh Huy; Deng, Zhigang; Eitan Grinspun and Jessica Hodgins
Most of current facial animation editing techniques are frame-based approaches (i.e., manually edit one keyframe every several frames), which is ineffective, time-consuming, and prone to editing inconsistency. In this paper, we present a novel facial editing style learning framework that is able to learn a constraint-based Gaussian Process model from a small number of facial-editing pairs, and then it can be effectively applied to automate the editing of the remaining facial animation frames or transfer editing styles between different animation sequences. Comparing with the state of the art, multiresolution-based mesh sequence editing technique, our approach is more flexible, powerful, and adaptive. Our approach can dramatically reduce the manual efforts required by most of current facial animation editing approaches.

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Browsing SCA 09: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "Computer Graphics [I.3.7]"

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