SCA 05: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/431

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Adapted Unstructured LBM for Flow Simulation on Curved Surfaces
(The Eurographics Association, 2005) Fan, Z.; Zhao, Y.; Kaufman, A.; He, Y.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
Flow motion on curved surfaces of arbitrary topology is an interesting visual effect but a complex dynamics to simulate. In this paper, we introduce a novel and effective way to model such dynamics. We propose a technique that adapts a recently emerged computational fluid dynamics (CFD) model, unstructured lattice Boltzmann model (Unstructured LBM), from the 2D unstructured meshes to the 3D surface meshes. Unlike previous methods in modeling flows on surfaces, which start from the macroscopic point of view and modify the Navier Stokes solvers for the curved surfaces, our method is based on the microscopic kinetic equations for discrete particle distribution functions. All computations on the surface mesh only involve the information within local neighborhoods. This model lends itself the following advantages: (i) simplicity and explicit parallelism in computation, (ii) great capability in handling complex interactions, such as the interactions between flow and boundaries and the interactions of multiple-component fluids; (iii) no need of global surface parameterization which may cause strong distortions; (iv) capability of being applied to meshes with arbitrary connectivity.
AER: Aesthetic Exploration and Refinement for Expressive Character Animation
(The Eurographics Association, 2005) Neff, Michael; Fiume, Eugene; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
Our progress in the problem of making animated characters move expressively has been slow, and it persists in being among the most challenging in computer graphics. Simply attending to the low-level motion control problem, particularly for physically based models, is very difficult. Providing an animator with the tools to imbue character motion with broad expressive qualities is even more ambitious, but it is clear it is a goal to which we must aspire. Part of the problem is simply finding the right language in which to express qualities of motion. Another important issue is that expressive animation often involves many disparate parts of the body, which thwarts bottom-up controller synthesis. We demonstrate progress in this direction through the specification of directed, expressive animation over a limited range of standing movements. A key contribution is that through the use of high-level concepts such as character sketches, actions and properties, which impose different modalities of character behaviour, we are able to create many different animated interpretations of the same script. These tools support both rapid exploration of the aesthetic space and detailed refinement. Basic character actions and properties are distilled from an extensive search in the performing arts literature. We demonstrate how all highlevel constructions for expressive animation can be given a precise semantics that translate into a low-level motion specification that is then simulated either physically or kinematically. Our language and system can act as a bridge across artistic and technical communities to resolve ambiguities regarding the language of motion.We demonstrate our results through an implementation and various examples.
Analyzing the Physical Correctness of Interpolated Human Motion
(The Eurographics Association, 2005) Safonova, Alla; Hodgins, Jessica K.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
Two human motions can be linearly interpolated to produce a new motion, giving the animator control over the length of a jump, the speed of walking, or the height of a kick. Over the past ten years, this simple technique has been shown to produce surprisingly natural looking results. In this paper, we analyze the motions produced by this technique for physical correctness and suggest small modifications to the standard interpolation technique that in some circumstances will produce significantly more natural looking motion.
Animosaics
(The Eurographics Association, 2005) Smithy, Kaleigh; Liuz, Yunjun; Klein, Allison; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
Animated mosaics are a traditional form of stop-motion animation created by arranging and rearranging small objects or tiles from frame to frame. While this animation style is uniquely compelling, the traditional process of manually placing and then moving tiles in each frame is time-consuming and labourious. Recent work has proposed algorithms for static mosaics, but generating temporally coherent mosaic animations has remained open. In addition, previous techniques for temporal coherence allow non-photorealistic primitives to layer, blend, deform, or scale, techniques that are unsuitable for mosaic animations. This paper presents a new approach to temporal coherence and applies this to build a method for creating mosaic animations. Specifically, we characterize temporal coherence as the coordinated movement of groups of primitives. We describe a system for achieving this coordinated movement to create temporally coherent geometric packings of 2D shapes over time. We also show how to create static mosaics comprised of different tile shapes using area-based centroidal Voronoi diagrams
An Art-Directed Wrinkle System for CG Character Clothing
(The Eurographics Association, 2005) Cutler, Lawrence D.; Gershbein, Reid; Wang, Xiaohuan Corina; Curtis, Cassidy; Maigret, Erwan; Prasso, Luca; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
We present a kinematic system for creating art-directed wrinkles on costumes for CG characters. This system employs a curve-based method for creating wrinkles on reference poses, which are incorporated into a weighted matching algorithm that generates wrinkle deformations on an animated character. The wrinkle creation tool is intuitive to use and accommodates art direction. The user can easily transfer wrinkle patterns to different characters, costumes, and body types. The algorithm for evaluating wrinkles measures the local stress of a surface and creates weights that are used to interpolate between the reference wrinkle patterns during movement. This algorithm is robust and efficient, and fits well into a large-scale feature-film production environment.
Autonomous Pedestrians
(The Eurographics Association, 2005) Shao, Wei; Terzopoulos, Demetri; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
We address the difficult open problem of emulating the rich complexity of real pedestrians in urban environments. Our artificial life approach integrates motor, perceptual, behavioral, and cognitive components within a model of pedestrians as individuals. Our comprehensive model features innovations in these components, as well as in their combination, yielding results of unprecedented fidelity and complexity for fully autonomous multi-human simulation in a large urban environment. We represent the environment using hierarchical data structures, which efficiently support the perceptual queries of the autonomous pedestrians that drive their behavioral responses and sustain their ability to plan their actions on local and global scales.
Behavior Planning for Character Animation
(The Eurographics Association, 2005) Lau, Manfred; Kuffner, James J.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
This paper explores a behavior planning approach to automatically generate realistic motions for animated characters. Motion clips are abstracted as high-level behaviors and associated with a behavior finite-state machine (FSM) that defines the movement capabilities of a virtual character. During runtime, motion is generated automatically by a planning algorithm that performs a global search of the FSM and computes a sequence of behaviors for the character to reach a user-designated goal position. Our technique can generate interesting animations using a relatively small amount of data, making it attractive for resource-limited game platforms. It also scales efficiently to large motion databases, because the search performance is primarily dependent on the complexity of the behavior FSM rather than on the amount of data. Heuristic cost functions that the planner uses to evaluate candidate motions provide a flexible framework from which an animator can control character preferences for certain types of behavior. We show results of synthesized animations involving up to one hundred human and animal characters planning simultaneously in both static and dynamic environments.
Capture and Synthesis of Insect Motion
(The Eurographics Association, 2005) Gibson, D. P.; Oziem, D. J.; Dalton, C. J.; Campbell, N. W.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
We present an integrated system that enables the capture and synthesis of 3D motions of small scale dynamic creatures, typically insects and arachnids, in order to drive computer generated models. The system consists of a number of stages, initially, the acquisition of a multi-view calibration scene and synchronised video footage of a subject performing some action is carried out. A user guided labelling process, that can be semi-automated using tracking techniques and a 3D point generating algorithm, then enables a full metric calibration and captures the motions of specific points on the subject. The 3D motions extracted, which often come from a limited number of frames of the original footage, are then extended to generate potentially infinitely long, characteristic motion sequences for multiple similar subjects. Finally a novel path following algorithm is used to find optimal path along with coherent motion for synthetic subjects. The result is a system that, from a potentially small number of original multi-view frames, can generate a whole swarm of novel synthetic subjects all moving in a coherent and natural manner. The proposed system has two major advantages over existing systems, 1) that traditional motion capture techniques cannot in general be used for very small subjects and 2) minimal expense and user input is required to generate, complex, high quality, CG animation.
Directable Animation of Elastic Objects
(The Eurographics Association, 2005) Kondo, Ryo; Kanai, Takashi; Anjyo, Ken-ichi; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
There is a crucial demand in the computer animation industry to make animations that blend animator-specified expressive motion with physics-based realism. We propose a novel framework to create directable animation of elastically deformable objects. The directable animation is created with animator-specified keyframes and the motion trajectory of the deformable object, while maintaining a plausible realism. Our framework mainly consists of two complementary approaches. The first is a method to control the time-varying geometry of an elastic object, using a loose key-framing technique. In our keyframing, we introduce an FEM-based elastic deformation algorithm that allows us to rearrange the elastic object motion, guided by the shape or pose specified at each keyframe. The second is a motion compensation technique, which allows us to rearrange the physical behavior of elastically deformable objects under a user-specified trajectory. The animation examples demonstrate that our framework provides plausibly realistic deformation animations with greater controllability and usability than existing approaches.
An Efficient Search Algorithm for Motion Data Using Weighted PCA
(The Eurographics Association, 2005) Forbes, K.; Fiume, E.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
Good motion data is costly to create. Such an expense often makes the reuse of motion data through transformation and retargetting a more attractive option than creating new motion from scratch. Reuse requires the ability to search automatically and efficiently a growing corpus of motion data, which remains a difficult open problem. We present a method for quickly searching long, unsegmented motion clips for subregions that most closely match a short query clip. Our search algorithm is based on a weighted PCA-based pose representation that allows for flexible and efficient pose-to-pose distance calculations. We present our pose representation and the details of the search algorithm. We evaluate the performance of a prototype search application using both synthetic and captured motion data. Using these results, we propose ways to improve the application s performance. The results inform a discussion of the algorithm s good scalability characteristics.
Fast and accurate goal-directed motion synthesis for crowds
(The Eurographics Association, 2005) Sung, Mankyu; Kovar, Lucas; Gleicher, Michael; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
This paper presents a highly efficient motion synthesis algorithm that is well suited for animating large numbers of characters. Given constraints that require characters to be in specific poses, positions, and orientations in specified time intervals, our algorithm synthesizes motions that exactly satisfy these constraints while avoiding inter-character collisions and collisions with the environment. We represent the space of possible actions with a motion graph and use search algorithms to generate motion. To provide a good initial guess for the search, we employ a fast path planner based on probabilistic roadmaps to navigate characters through complex environments. Also, unlike existing algorithms, our search process allows for smooth, continual adjustments to position, orientation, and timing. This allows us both to satisfy constraints precisely and to generate motion much faster than would otherwise be possible.
Group Motion Graphs
(The Eurographics Association, 2005) Lai, Yu-Chi; Chenney, Stephen; Fan, Shao Hua; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
We introduce Group Motion Graphs, a data-driven animation technique for groups of discrete agents, such as flocks, herds, or small crowds. Group Motion Graphs are conceptually similar to motion graphs constructed from motion-capture data, but have some important differences: we assume simulated motion; transition nodes are found by clustering group configurations from the input simulations; and clips to join transitions are explicitly constructed via constrained simulation. Graphs built this way offer known bounds on the trajectories that they generate, making it easier to search for particular output motions. The resulting animations show realistic motion at significantly reduced computational cost compared to simulation, and improved control.
Helping Hand: An Anatomically Accurate Inverse Dynamics Solution For Unconstrained Hand Motion
(The Eurographics Association, 2005) Tsang, Winnie; Singh, Karan; Fiume, Eugene; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
We present a realistic skeletal musculo-tendon model of the human hand and forearm. The model permits direct forward dynamics simulation, which accurately predicts hand and finger position given a set of muscle activations. We also present a solution to the inverse problem of determining an optimal set of muscle activations to achieve a given pose or motion; muscle fatigue, injury or atrophy can also be specified, yielding different control solutions that favour healthy muscle. As there can be many (or no) solutions to this inverse problem, we demonstrate how the space of possible solutions can be filtered to an optimal representative. Of particular note is the ability of our model to take a wide array of joint interdependence into account for both forward and inverse problems. Given kinematic postures, the model can be used to validate, predict or fill in missing motion and improve coarsely specified motion with anatomic fidelity. Lastly, we address the visualization and understanding of the dynamically changing and spatially compact musculature using various interaction techniques.
Imitation as a First Step to Social Learning in Synthetic Characters: A Graph-based Approach
(The Eurographics Association, 2005) Buchsbaum, D.; Blumberg, B.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
The processes and representations used to generate the behavior of expressive virtual characters are a valuable and largely untapped resource for helping those characters make sense of the world around them. In this paper, we present Max T. Mouse, an anthropomorphic animated mouse character who uses his own motor and behavior representations to interpret the behaviors he sees his friend Morris Mouse performing. Specifically, by using his own motor and action systems as models for the behavioral capabilities of others (a process known as Simulation Theory in the cognitive literature), Max can begin to identify simple goals and motivations for Morris s behavior, an important step towards developing socially intelligent animated characters. Additionally, Max uses a novel motion graph-based movement recognition process in order to accurately parse and imitate Morris s movements and behaviors in real-time and without prior examples, even when provided with limited synthetic visual input. Key contributions of this paper include demonstrating that using the same mechanisms for movement and behavior perception and production allows for an elegant conservation of representation, and that the innate structure of motion graphs can be used to facilitate both movement parsing and movement recognition.
Modeling and Animating Gases with Simulation Features
(The Eurographics Association, 2005) Schpok, Joshua; Dwyer, William; Ebert, David S.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
In modeling natural phenomena, artists often compromise the benefits of direct control for the visual realism of physics-based simulation. For gases, Eulerian simulations traditionally provide realistic results, but a poor representation for artistically shaping the media. In our system, users work with a more intuitive set of continuously extracted features whose manipulation feeds back into the original simulation. This novel approach overcomes common control issues by providing modeling tools to manipulate high-level behavior in Eulerian simulations. We employ techniques in feature extraction, real-time gas simulation, and volume rendering to build an interactive system to sculpt three-dimensional flows.
Morphable model of quadrupeds skeletons for animating 3D animals
(The Eurographics Association, 2005) Reveret, Lionel; Favreau, Laurent; Depraz, Christine; Cani, Marie-Paule; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
Skeletons are at the core of 3D character animation. The goal of this work is to design a morphable model of 3D skeleton for four footed animals, controlled by a few intuitive parameters. This model enables the automatic generation of an animation skeleton, ready for character rigging, from a few simple measurements performed on the mesh of the quadruped to animate. Quadruped animals - usually mammals - share similar anatomical structures, but only a skilled animator can easily translate them into a simple skeleton convenient for animation. Our approach for constructing the morphable model thus builds on the statistical learning of reference skeletons designed by an expert animator. This raises the problems of coping with data that includes both translations and rotations, and of avoiding the accumulation of errors due to its hierarchical structure. Our solution relies on a quaternion representation for rotations and the use of a global frame for expressing the skeleton data. We then explore the dimensionality of the space of quadruped skeletons, which yields the extraction of three intuitive parameters for the morphable model, easily measurable on any 3D mesh of a quadruped. We evaluate our method by comparing the predicted skeletons with user-defined ones on one animal example that was not included into the learning database. We finally demonstrate the usability of the morphable skeleton model for animation.
Motion Modeling for On-Line Locomotion Synthesis
(The Eurographics Association, 2005) Kwon, Taesoo; Shiny, Sung Yong; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
In this paper, we propose an example-based approach to on-line locomotion synthesis. Our approach consists of two parts: motion analysis and motion synthesis. In the motion analysis part, an unlabeled motion sequence is first decomposed into motion segments, exploiting the behavior of the COM (center of mass) trajectory of the performer. Those motion segments are subsequently classified into groups of motion segments such that the same group of motion segments share an identical footstep pattern. Finally, we construct a hierarchical motion transition graph by representing these groups and their connectivity to other groups as nodes and edges, respectively. The coarse level of this graph models locomotive motions and their transitions, and the fine level mainly captures the cyclic nature of locomotive motions. In the motion synthesis part, given a stream of motion specifications in an on-line manner, the motion transition graph is traversed while blending the motion segments to synthesize a motion at a node, one by one, guided by the motion specifications. Our main contributions are the motion labeling scheme and a new motion model, embodied by the hierarchical motion transition graph, which together enable not only artifact-free motion blending but also seamless motion transition.
Outside-In Anatomy Based Character Rigging
(The Eurographics Association, 2005) Pratscher, Michael; Coleman, Patrick; Laszlo, Joe; Singh, Karan; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
For believable character animation, skin deformation should communicate important deformation effects due to underlying muscle movement. Anatomical models that capture these effects are typically constructed from the inside out. Internal tissue is modeled by hand and a surface skin is attached to, or generated from, the internal structure. This paper presents an outside in approach to anatomical modeling, in which we generate musculature from a predefined structure, which we conform to an artist sculpted skin surface. Motivated by interactive applications, we attach the musculature to an existing control skeleton and apply a novel geometric deformation model to deform the skin surface to capture important muscle motion effects. Musculoskeletal structure can be stored as a template and applied to new character models. We illustrate the methodology, as integrated into a commercial character animation system, with examples driven by both keyframe animation and recorded motion data.
Particle-Based Fluid-Fluid Interaction
(The Eurographics Association, 2005) Müller, Matthias; Solenthaler, Barbara; Keiser, Richard; Gross, Markus; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
The interesting and complex behavior of fluids emerges mainly from interaction processes. While interactions of fluids with static or dynamic solids has caught some attention in computer graphics lately, the mutual interaction of different types of fluids such as air and water or water and wax has received much less attention although these types of interaction are the basis for a variety of important phenomena. In this paper we propose a new technique to model fluid-fluid interaction based on the Smoothed Particle Hydrodynamics (SPH) method. For the simulation of air-water interaction, air particles are generated on the fly only where needed. We also model dynamic phase changes and interface forces. Our technique makes possible the simulation of phenomena such as boiling water, trapped air and the dynamics of a lava lamp.
Particle-Based Simulation of Granular Materials
(The Eurographics Association, 2005) Bell, Nathan; Yu, Yizhou; Mucha, Peter J.; D. Terzopoulos and V. Zordan and K. Anjyo and P. Faloutsos
Granular materials, such as sand and grains, are ubiquitous. Simulating the 3D dynamic motion of such materials represents a challenging problem in graphics because of their unique physical properties. In this paper we present a simple and effective method for granular material simulation. By incorporating techniques from physical models, our approach describes granular phenomena more faithfully than previous methods. Granular material is represented by a large collection of non-spherical particles which may be in persistent contact. The particles represent discrete elements of the simulated material. One major advantage of using discrete elements is that the topology of particle interaction can evolve freely. As a result, highly dynamic phenomena, such as splashing and avalanches, can be conveniently generated by this meshless approach without sacrificing physical accuracy. We generalize this discrete model to rigid bodies by distributing particles over their surfaces. In this way, two-way coupling between granular materials and rigid bodies is achieved.

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