SCA 06: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/430

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MotionMaster: Authoring and Choreographing Kung-fu Motions by Sketch Drawings
(The Eurographics Association, 2006) Li, Qilei L.; Geng, Weidong D.; Yu, Tao; Shen, Xiao Jie; Lau, Newman; Yu, Gino; Marie-Paule Cani and James O'Brien
Sketch-drawings is an intuitive and comprehensive means of conveying movement ideas in character animation. We proposed a novel sketch-based approach to assisting the authoring and choreographing of Kungfu motions at the early stage of animation creation. Given two human figure sketches corresponding to the initial and closing posture of a Kungfu form, and the trajectory drawings on specific moving joints, MotionMaster can directly rapidprototype the realistic 3D motion sequence by sketch-based motion retrieval and refinement based on a motion database. The animators can then preview and evaluate the recovered motion sequence from any viewing angles. After the 3D motion sequence has been associated with the 2D sketch drawing, the animator can also interactively and iteratively make changes on the 2D sketch drawing, and the system will automatically transfer the 2D changes to the 3D motion data of current interests. It greatly helps the animator focus on the movement idea development during the evolutionary process of building motion data for articulated characters.
Robust Kinematic Constraint Detection for Motion Data
(The Eurographics Association, 2006) Callennec, Benoît Le; Boulic, Ronan; Marie-Paule Cani and James O'Brien
Motion capture data is now widely available to create realistic character animation. However, it is di?cult to reuse without any additional information. For this reason, annotating motion data with kinematic constraints is a clever step to ease further operations such as blending or motion editing. Unfortunately, prior automatic methods prove to be unreliable for noisy data and/or lack genericity. In this paper, we present a method for detecting kinematic constraints for motion data. It detects when an object (or an end-e?ector) is stationary in space or is rotating around an axis or a point. Our method is fast, generic and may be used on any kind of objects in the scene. Furthermore, it is robust to highly noisy data as we detect and reject aberrant data by using a least median of squares (LMedS) method. We demonstrate the accuracy of our method in various motion editing contexts.
Fat Graphs: Constructing an Interactive Character with Continuous Controls
(The Eurographics Association, 2006) Shin, Hyun Joon; Oh, Hyun Seok; Marie-Paule Cani and James O'Brien
This paper proposes a methodology that allows users to control character s motion interactively but continuously. Inspired by the work of Gleicher et al. [GSKJ03], we propose a semi-automatic method to build fat graphs where a node corresponds to a pose and its incoming and outgoing edges represent the motion segments starting from and ending at similar poses. A group of edges is built into a fat edge that parameterizes similar motion segments into a blendable form. Employing the existing motion transition and blending methods, our run-time system allows users to control a character interactively in continuous parameter spaces with conventional input devices such as joysticks and the mice. The capability of the proposed methodology is demonstrated through several applications. Although our method has some limitations on motion repertories and qualities, it can be adapted to a number of real-world applications including video games and virtual reality applications.
Precomputed Search Trees: Planning for Interactive Goal-Driven Animation
(The Eurographics Association, 2006) Lau, Manfred; Kuffner, James J.; Marie-Paule Cani and James O'Brien
We present a novel approach for interactively synthesizing motions for characters navigating in complex environments. We focus on the runtime efficiency for motion generation, thereby enabling the interactive animation of a large number of characters simultaneously. The key idea is to precompute search trees of motion clips that can be applied to arbitrary environments. Given a navigation goal relative to a current body position, the best available solution paths and motion sequences can be efficiently extracted during runtime through a series of table lookups. For distant start and goal positions, we first use a fast coarse-level planner to generate a rough path of intermediate sub-goals to guide each iteration of the runtime lookup phase. We demonstrate the efficiency of our technique across a range of examples in an interactive application with multiple autonomous characters navigating in dynamic environments. Each character responds in real-time to arbitrary user changes to the environment obstacles or navigation goals. The runtime phase is more than two orders of magnitude faster than existing planning methods or traditional motion synthesis techniques. Our technique is not only useful for autonomous motion generation in games, virtual reality, and interactive simulations, but also for animating massive crowds of characters offline for special effects in movies.
Interactive Animation of Dynamic Manipulation
(The Eurographics Association, 2006) Abe, Yeuhi; Popovic, Jovan; Marie-Paule Cani and James O'Brien
Lifelike animation of object manipulation requires dynamic interaction between animated characters, objects, and their environment. These interactions can be animated automatically with physically based simulations but proper controls are needed to animate characters that move realistically and that accomplish tasks in spite of unexpected disturbances. This paper describes an efficient control algorithm that generates realistic animations by incorporating motion data into task execution. The end result is a versatile system for interactive animation of dynamic manipulation tasks such as lifting, catching, and throwing.
Progressive Deforming Meshes based on Deformation Oriented Decimation and Dynamic Connectivity Updating
(The Eurographics Association, 2006) Huang, Fu-Chung; Chen, Bing-Yu; Chuang, Yung-Yu; Marie-Paule Cani and James O'Brien
We present a method for progressive deforming meshes. Most existing mesh decimation methods focus on static meshes. However, there are more and more animation data today, and it is important to address the problem of simplifying deforming meshes. Our method is based on deformation oriented decimation (DOD) error metric and dynamic connectivity updating (DCU) algorithm. Deformation oriented decimation extends the deformation sensitivity decimation (DSD) error metric by augmenting an additional term to model the distortion introduced by deformation. This new metric preserves not only geometric features but also areas with large deformation. Using this metric, a static reference connectivity is extracted for the whole animation. Dynamic connectivity updating algorithm utilizes vertex trees to further reduce geometric distortion by allowing the connectivity to change. Tem- poral coherence in the dynamic connectivity between frames is achieved by penalizing large deviations from the reference connectivity. The combination of DOD and DCU demonstrates better simplification and triangulation performance than previous methods for deforming mesh simplification.
"Walk to here": A Voice Driven Animation System
(The Eurographics Association, 2006) Wang, Zhijin; Panne, Michiel van de; Marie-Paule Cani and James O'Brien
We present a novel interface for directing the actions of computer animated characters and camera movements. Our system takes spoken input in combination with mouse pointing to generate desired character animation based on motion capture data. The aim is to achieve a more natural animation interface by supporting the types of dialogue and pointing that might be used when one person is explaining a desired motion to another person. We compare our voice-driven system with a button-driven animation interface that has equivalent capabilities. An informal user study indicates that for the test scenarios, the voice-user interface (VUI) is faster than an equivalent graphical user interface (GUI). Potential applications include storyboarding for film or theatre, directing characters in video games, and scene reconstruction.
Simulating Speech with a Physics-Based Facial Muscle Model
(The Eurographics Association, 2006) Sifakis, Eftychios; Selle, Andrew; Robinson-Mosher, Avram; Fedkiw, Ronald; Marie-Paule Cani and James O'Brien
We present a physically based system for creating animations of novel words and phrases from text and audio input based on the analysis of motion captured speech examples. Leading image based techniques exhibit photo-real quality, yet lack versatility especially with regard to interactions with the environment. Data driven approaches that use motion capture to deform a three dimensional surface often lack any anatomical or physically based structure, limiting their accuracy and realism. In contrast, muscle driven physics-based facial animation systems can trivially integrate external interacting objects and have the potential to produce very realistic animations as long as the underlying model and simulation framework are faithful to the anatomy of the face and the physics of facial tissue deformation. We start with a high resolution, anatomically accurate flesh and muscle model built for a specific subject. Then we translate a motion captured training set of speech examples into muscle activation signals, and subsequently segment those into intervals corresponding to individual phonemes. Finally, these samples are used to synthesize novel words and phrases. The versatility of our approach is illustrated by combining this novel speech content with various facial expressions, as well as interactions with external objects.
Motion Templates for Automatic Classification and Retrieval of Motion Capture Data
(The Eurographics Association, 2006) Müller, Meinard; Röder, Tido; Marie-Paule Cani and James O'Brien
This paper presents new methods for automatic classification and retrieval of motion capture data facilitating the identification of logically related motions scattered in some database. As the main ingredient, we introduce the concept of motion templates (MTs), by which the essence of an entire class of logically related motions can be captured in an explicit and semantically interpretable matrix representation. The key property of MTs is that the variable aspects of a motion class can be automatically masked out in the comparison with unknown motion data. This facilitates robust and efficient motion retrieval even in the presence of large spatio-temporal variations. Furthermore, we describe how to learn an MT for a specific motion class from a given set of training motions. In our extensive experiments, which are based on several hours of motion data, MTs proved to be a powerful concept for motion annotation and retrieval, yielding accurate results even for highly variable motion classes such as cartwheels, lying down, or throwing motions.
Automatic Splicing for Hand and Body Animations
(The Eurographics Association, 2006) Majkowska, Anna; Zordan, Victor B.; Faloutsos, Petros; Marie-Paule Cani and James O'Brien
We propose a solution to a new problem in animation research: how to use human motion capture data to create character motion with detailed hand gesticulation without the need for the simultaneous capture of hands and the full-body. Occlusion and a difference in scale make it difficult to capture both the detail of the hand movement and unrestricted full-body motion at the same time. With our method, the two can be captured separately and spliced together seamlessly with little or no user input required. The algorithm relies on a novel distance metric derived from research on gestures and uses a two-pass dynamic time warping algorithm to find correspondence between the hand and full-body motions. In addition, we provide a method for supplying user input, useful to animators who want more control over the integrated animation. We show the power of our technique with a variety of common and highly specialized gesticulation examples.
Simple Linear Bending Stiffness in Particle Systems
(The Eurographics Association, 2006) Volino, Pascal; Magnenat-Thalmann, Nadia; Marie-Paule Cani and James O'Brien
In cloth simulation particle systems models, bending stiffness involve forces which are either represented as additional springs, or as out-of-plane forces along surface normals. While the former solution is quite inaccurate for both small and large curvatures, the latter requires significant computation and is unsuited for fast computation required by real-time or interactive systems. We present a linear approach which combines simplicity and accuracy, being perfectly suited for the implicit integration schemes used in particle systems.
Perceptual Evaluation of LOD Clothing for Virtual Humans
(The Eurographics Association, 2006) McDonnell, Rachel; Dobbyn, Simon; Collins, Steven; O'Sullivan, Carol; Marie-Paule Cani and James O'Brien
Recent developments in crowd simulation have allowed thousands of characters to be rendered in real-time. Usually this is achieved through the use of Level of Detail (LOD) models for the individuals in the crowd. Perceptual studies have shown that image-based representations, i.e., impostors, can be used as imperceptible background substitutes for high-polygon models for skinned human characters, resulting in optimal rendering times and high visual fidelity. However, previous methods only showed humans dressed in clothes that were deformed using standard skinning methods. Highly deformable objects like cloth are not effectively depicted using these methods. Therefore, in this paper, we present the first perceptual evaluation of different LOD representations of humans wearing deformable (i.e., physically simulated) clothing. We show conclusively that impostors are startlingly effective at depicting the deformation properties of clothing and present useful guidelines for the development of crowd systems with thousands of realistically clothed humans.
Fast Simulation of Deformable Models in Contact Using Dynamic Deformation Textures
(The Eurographics Association, 2006) Galoppo, Nico; Otaduy, Miguel A.; Mecklenburg, Paul; Gross, Markus; Lin, Ming C.; Marie-Paule Cani and James O'Brien
We present an efficient algorithm for simulating contacts between deformable bodies with high-resolution surface geometry using dynamic deformation textures, which reformulate the 3D elastoplastic deformation and collision handling on a 2D parametric atlas to reduce the extremely high number of degrees of freedom in such a computa- tionally demanding simulation. We perform proximity queries for deformable bodies using a two-stage algorithm directly on dynamic deformation textures, resulting in output-sensitive collision detection that is independent of the combinatorial complexity of the deforming meshes. We present a robust, parallelizable formulation for computing constraint forces using implicit methods that exploits the structure of the motion equations to achieve highly stable simulation, while taking large time steps with inhomogeneous materials. The dynamic deformation textures can also be used directly for real-time shading and can easily be implemented using SIMD architecture on commodity hardware. We show that our approach, complementing existing pioneering work, offers significant computational advantages on challenging contact scenarios in dynamic simulation of deformable bodies.
Learning a Correlated Model of Identity and Pose-Dependent Body Shape Variation for Real-Time Synthesis
(The Eurographics Association, 2006) Allen, Brett; Curless, Brian; Popovic, Zoran; Hertzmann, Aaron; Marie-Paule Cani and James O'Brien
We present a method for learning a model of human body shape variation from a corpus of 3D range scans. Our model is the first to capture both identity-dependent and pose-dependent shape variation in a correlated fashion, enabling creation of a variety of virtual human characters with realistic and non-linear body deformations that are customized to the individual. Our learning method is robust to irregular sampling in pose-space and identityspace, and also to missing surface data in the examples. Our synthesized character models are based on standard skinning techniques and can be rendered in real time.
Simultaneous Coupling of Fluids and Deformable Bodies
(The Eurographics Association, 2006) Chentanez, Nuttapong; Goktekin, Tolga G.; Feldman, Bryan E.; O'Brien, James F.; Marie-Paule Cani and James O'Brien
This paper presents a method for simulating the two-way interaction between fluids and deformable solids. The fluids are simulated using an incompressible Eulerian formulation where a linear pressure projection on the fluid velocities enforces mass conservation. Similarly, elastic solids are simulated using a semi-implicit integrator implemented as a linear operator applied to the forces acting on the nodes in Lagrangian formulation. The proposed method enforces coupling constraints between the fluid and the elastic systems by combining both the pressure projection and implicit integration steps into one set of simultaneous equations. Because these equations are solved simultaneously the resulting combined system treats closed regions in a physically correct fashion, and has good stability characteristics allowing for relatively large time steps. This general approach is not tied to any particular volume discretization of fluid or solid, and we present results implemented using both regular-grid and tetrahedral simulations.
Oriented Strands - Dynamics of Stiff Multi-Body System
(The Eurographics Association, 2006) Hadap, Sunil; Marie-Paule Cani and James O'Brien
The simulation of strand like primitives modeled as dynamics of serial branched multi-body chain, albeit a potential reduced coordinate formulation, gives rise to stiff and highly non-linear differential equations. We introduce a recursive, linear time and fully implicit method to solve the stiff dynamical problem arising from such a multi-body system. We augment the merits of the proposed scheme by means of analytical constraints and an elaborate collision response model. We finally discuss a versatile simulation system based on the strand primitive for character dynamics and visual effects. We demonstrate dynamics of ears, braid, long/curly hair and foliage.
Physics Based Boiling Simulation
(The Eurographics Association, 2006) Mihalef, Viorel; Unlusu, Betul; Metaxas, Dimitris; Sussman, Mark; Hussaini, M. Y.; Marie-Paule Cani and James O'Brien
In order to animate complex fluid motion, computer animators have to rely on simulation systems that automatically generate the dynamics in a physics based manner. We focus in this paper on the phenomenon of boiling, which, due to its complex formulation and physics, has seen very little work done in the graphics field. We propose a new Eulerian method that couples gas and liquid with variable temperature and with a mass transfer mechanism, and we present its application to simulating boiling phenomena. Our philosophy is using physics based models to obtain visually rich animations that mirror their real life counterparts, including phenomena of increased circulation in the mass of liquid, roiling boil, nucleation seeding on solid boundaries.
Modeling Ice Dynamics As A Thin-Film Stefan Problem
(The Eurographics Association, 2006) Kim, Theodore; Adalsteinsson, David; Lin, Ming C.; Marie-Paule Cani and James O'Brien
Large, 3D ice formations such as icicles exhibit a high degree of geometric and optical complexity. Modeling these features by hand can be a daunting task, so we present a novel physically-based algorithm for simulating this phenomenon. Solidification is usually posed as a so-called Stefan problem , but the problem in its classic form is inappropriate for simulating the ice typically found in a winter scene. We instead use the thin-film variant of the Stefan problem to derive velocity equations for a level set simulation. However, due to the scales involved in the problem, even an adaptive grid level set solver is still insufficient to track the tip of an icicle. Therefore, we derive an analytical solution for the icicle tip and use it to correct the level set simulation. The results appear to be in agreement with experimental data. We also present a physically-based technique for modeling ripples along the ice surface that alleviates the need to explicitly track small-scale geometry. To our knowledge, our approach is the most complete model available, and produces complex visual phenomena that no previous method has been able to capture.
Simulation of Bubbles
(The Eurographics Association, 2006) Zheng, Wen; Yong, Jun-Hai; Paul, Jean-Claude; Marie-Paule Cani and James O'Brien
We present a novel framework based on a continuous fluid simulator for general simulation of realistic bubbles, with which we can handle as many significant dynamic bubble effects as possible. To capture nature of the very thin liquid film of bubbles, we have developed a regional level set method allowing multi-manifold interface tracking. The regional level set method is based on the definitions of regional distance and its five operators, which makes it very easy to implement. We can reconstruct an implicit surface of liquid film with arbitrary thickness from the representation of regional level set functions. To overcome the numerical instability caused by surface tension, we exploit a new semi-implicit surface tension model which is unconditionally stable and makes the simulation of surface tension dominated phenomena much more efficient. An approximated film thickness evolution model is proposed to control the bubble s lifecycle. All these new techniques combine into a general framework that can produce various realistic dynamic effects of bubbles.
A Texture Synthesis Method for Liquid Animations
(The Eurographics Association, 2006) Bargteil, Adam W.; Sin, Funshing; Michaels, Jonathan E.; Goktekin, Tolga G.; O'Brien, James F.; Marie-Paule Cani and James O'Brien
In this paper we present a method for synthesizing textures on animated liquid surfaces generated by a physically based fluid simulation system. Rather than advecting texture coordinates on the surface, our algorithm synthesizes a new texture for every frame using an optimization procedure which attempts to match the surface texture to an input sample texture. By synthesizing a new texture for every frame, our method is able to overcome the discontinuities and distortions of an advected parameterization. We achieve temporal coherence by initializing the surface texture with color values advected from the surface at the previous frame and including these colors in the energy function used during optimization.

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