SCA 12: Eurographics/SIGGRAPH Symposium on Computer Animation

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/424

Browse

Now showing 1 - 20 of 23

Cloning Crowd Motions
(The Eurographics Association, 2012) Li, Yi; Christie, Marc; Siret, Orianne; Kulpa, Richard; Pettré, Julien; Jehee Lee and Paul Kry
This paper introduces a method to clone crowd motion data. Our goal is to efficiently animate large crowds from existing examples of motions of groups of characters by applying an enhanced copy and paste technique on them. Specifically, we address spatial and temporal continuity problems to enable animation of significantly larger crowds than our initial data. We animate many characters from the few examples with no limitation on duration. Moreover, our animation technique answers the needs of real-time applications through a technique of linear complexity. Therefore, it is significantly more efficient than any existing crowd simulation-based technique, and in addition, we ensure a predictable level of realism for animations. We provide virtual population designers and animators with a powerful framework which (i) enables them to clone crowd motion examples while preserving the complexity and the aspect of group motion and (ii) is able to animate large-scale crowds in real-time. Our contribution is the formulation of the cloning problem as a double search problem. Firstly, we search for almost periodic portions of crowd motion data through the available examples. Secondly, we search for almost symmetries between the conditions at the limits of these portions in order to interconnect them. The result of our searches is a set of crowd patches that contain portions of example data that can be used to compose large and endless animations. Through several examples prepared from real crowd motion data, we demonstrate the advantageous properties of our approach as well as identify its potential for future developments.
Combining Marker-based Mocap and RGB-D Camera for Acquiring High-fidelity Hand Motion Data
(The Eurographics Association, 2012) Zhao, Wenping; Chai, Jinxiang; Xu, Ying-Qing; Jehee Lee and Paul Kry
Motion capture data has been pivotal to the success of creating realistic animation for human characters. There are a number of public full-body motion databases available, but large and heterogeneous databases for hand articulations are not available. In this paper, we introduce a novel acquisition framework for acquiring a wide range of high-fidelity hand motion data. Our key idea is to leverage marker position data recorded by a twelvecamera optical motion capture system and RGB/Depth data obtained from a single Microsoft Kinect camera. We formulate the hand motion capture problem in a nonlinear optimization framework by maximizing consistency between the reconstructed motion and observed measurement. We introduce an efficient optimization technique to estimate the optimal hand pose that best matches observed data.We have demonstrated the power and effectiveness of our system by capturing a wide variety of delicate hand articulations, even in case of significant self-occlusion.
Component-based Locomotion Composition
(The Eurographics Association, 2012) Kim, Yejin; Neff, Michael; Jehee Lee and Paul Kry
When generating locomotion, it is particularly challenging to adjust the motion's style. This paper introduces a component-based system for human locomotion composition that drives off a set of example locomotion clips. The distinctive style of each example is analyzed in the form of sub-motion components decomposed from separate body parts via independent component analysis (ICA). During the synthesis process, we use these components as combinatorial ingredients to generate new locomotion sequences that are stylistically different from the example set. Our system is designed for novice users who do not have much knowledge of important locomotion properties, such as the correlations throughout the body. Thus, the proposed system analyzes the examples in a unsupervised manner and synthesizes an output locomotion from a small number of control parameters. Our experimental results show that the system can generate physically plausible locomotion in a desired style at interactive speed.
Contact-Invariant Optimization for Hand Manipulation
(The Eurographics Association, 2012) Mordatch, Igor; Popovic, Zoran; Todorov, Emanuel; Jehee Lee and Paul Kry
We present a method for automatic synthesis of dexterous hand movements, given only high-level goals specifying what should happen to the object being manipulated. Results are presented on a wide range of tasks including grasping and picking up objects, twirling them between the fingers, tossing and catching, drawing. This work is an extension of the recent contact-invariant optimization (CIO) method, which introduced auxiliary decision variables directly specifying when and where contacts should occur, and optimized these variables together with the movement trajectory. Our contribution here is extending the unique contact model used in CIO which was specific to locomotion tasks, as well as applying the extended method systematically to hand manipulation.
Controlling Liquids Using Meshes
(The Eurographics Association, 2012) Raveendran, Karthik; Thuerey, Nils; Wojtan, Chris; Turk, Greg; Jehee Lee and Paul Kry
We present an approach for artist-directed animation of liquids using multiple levels of control over the simulation, ranging from the overall tracking of desired shapes to highly detailed secondary effects such as dripping streams, separating sheets of fluid, surface waves and ripples. The first portion of our technique is a volume preserving morph that allows the animator to produce a plausible fluid-like motion from a sparse set of control meshes. By rasterizing the resulting control meshes onto the simulation grid, the mesh velocities act as boundary conditions during the projection step of the fluid simulation. We can then blend this motion together with uncontrolled fluid velocities to achieve a more relaxed control over the fluid that captures natural inertial effects. Our method can produce highly detailed liquid surfaces with control over sub-grid details by using a mesh-based surface tracker on top of a coarse grid-based fluid simulation. We can create ripples and waves on the fluid surface attracting the surface mesh to the control mesh with spring-like forces and also by running a wave simulation over the surface mesh. Our video results demonstrate how our control scheme can be used to create animated characters and shapes that are made of water.
Enriching Coarse Interactive Elastic Objects with High-Resolution Data-Driven Deformations
(The Eurographics Association, 2012) Seiler, Martin; Spillmann, Jonas; Harders, Matthias; Jehee Lee and Paul Kry
Efficient approximate deformation models allow to interactively simulate elastic objects. However, these approaches usually cannot reproduce the complex deformation behavior governed by geometric and material nonlinearities. In addition, objects having slender shapes require dense simulation meshes, which necessitates additional computational effort. We propose an approach where a dynamic interactive coarse simulation is enriched with details stemming from a more accurate quasi-static simulation in a data-driven way. While the coarse simulation is based on a low-resolution (low-res) mesh and a fast linear deformation model the accurate simulation employs a quasi-static non-linear deformation model at a higher mesh resolution (high-res). We pre-compute pairs of low-res mesh deformations and corresponding high-res details by applying a series of training interactions on both the coarse and the accurate model. At run-time, we only run the coarse simulation and correlate the current state to the training states. Subsequently, we blend detail data in order to obtain a spatio-temporally smooth displacement field that we super-impose on the surface skin, resulting in a plausible display of the non-linearly deformed object at real-time rates. We present examples from both computer animation and medical simulation.
Environment-aware Real-Time Crowd Control
(The Eurographics Association, 2012) Henry, Joseph; Shum, Hubert P. H.; Komura, Taku; Jehee Lee and Paul Kry
Real-time crowd control has become an important research topic due to the recent advancement in console game quality and hardware processing capability. The degrees of freedom of a crowd is much higher than that provided by a standard user input device. As a result most crowd control systems require the user to design the crowd move- ments through multiple passes, such as first specifying the crowd's start and goal points, then providing the agent trajectories with streamlines. Such a multi-pass control would spoil the responsiveness and excitement of real- time games. In this paper, we propose a new, single-pass algorithm to control crowds using a deformable mesh. When controlling crowds, we observe that most of the low level details are related to passive interactions between the crowd and the environment, such as obstacle avoidance and diverging/merging at cross points. Therefore, we simplify the crowd control problem by representing the crowd with a deformable mesh that passively reacts to the environment. As a result, the user can focus on high level control that is more important for context delivery. Our algorithm provides an efficient crowd control framework while maintaining the quality of the simulation, which is useful for real-time applications such as strategy games.
Evaluating the Plausibility of Edited Throwing Animations
(The Eurographics Association, 2012) Vicovaro, Michele; Hoyet, Ludovic; Burigana, Luigi; O'Sullivan, Carol; Jehee Lee and Paul Kry
Animation budget constraints during the development of a game often call for the use of a limited set of generic motions. Editing operations are thus generally required to animate virtual characters with a sufficient level of variety. Evaluating the perceptual plausibility of edited animations can therefore contribute greatly towards producing visually plausible animations. In this paper we study observers' sensitivity to manipulations of overarm and underarm biological throwing animations. In our first experiment, we used Dynamic Time Warping to edit the biological throwing motions, and modified the release velocity of the ball accordingly. We found that observers are more tolerant to speeding up of the original throwing motion than to slowing down, and that slowed down underarm throws are perceived as particularly unnatural. In our second experiment, we modified separately horizontal and vertical components of the release velocity of the ball, while leaving the motion of the thrower unchanged. We found that observers are more sensitive to manipulations of the horizontal component in overarm throws, and of the vertical component in underarm throws. As in the first experiment, we found that observers are most disturbed by decreases in the velocity of the ball in underarm throws. Our results provide valuable insights for developers of games and VR applications by specifying thresholds for the perceptual plausibility of throwing manipulations.
Faster Acceleration Noise for Multibody Animations using Precomputed Soundbanks
(The Eurographics Association, 2012) Chadwick, Jeffrey N.; Zheng, Changxi; James, Doug L.; Jehee Lee and Paul Kry
We introduce an efficient method for synthesizing rigid-body acceleration noise for complex multibody scenes. Existing acceleration noise synthesis methods for animation require object-specific precomputation, which is prohibitively expensive for scenes involving rigid-body fracture or other sources of small, procedurally generated debris. We avoid precomputation by introducing a proxy-based method for acceleration noise synthesis in which precomputed acceleration noise data is only generated for a small set of ellipsoidal proxies and stored in a proxy soundbank. Our proxy model is shown to be effective at approximating acceleration noise from scenes with lots of small debris (e.g., pieces produced by rigid-body fracture). This approach is not suitable for synthesizing acceleration noise from larger objects with complicated non-convex geometry; however, it has been shown in previous work that acceleration noise from objects such as these tends to be largely masked by modal vibration sound. We manage the cost of our proxy soundbank with a new wavelet-based compression scheme for acceleration noise and use our model to significantly improve sound synthesis results for several multibody animations.
Finger Walking: Motion Editing with Contact-Based Hand Performance
(The Eurographics Association, 2012) Lockwood, Noah; Singh, Karan; Jehee Lee and Paul Kry
We present a system for generating full-body animations from the performance on a touch-sensitive tabletop of ''finger walking'', where two fingers are used to pantomime leg movements. A user study was conducted to explore how users can communicate full-body motion using their hands, which concluded that finger walking is a naturally-chosen and comfortable performance method. Based on contact data recorded during this study, the properties of a variety of performed locomotion types were analyzed to determine which motion parameters are most reliable and expressive for the purpose of generating corresponding full-body animations. Based on this analysis, a compact set of motion features was developed for classifying the locomotion type of a finger performance. A prototype interactive animation system was implemented to generate full-body animations of a known locomotion type from finger walking by estimating the motion path of a finger performance, and editing the path of a corresponding animation to match. The classification accuracy and output animation quality of this system was evaluated in a second user study, demonstrating that satisfying full-body animations can be reliably generated from finger performances.
The Intersection Contour Minimization Method for Untangling Oriented Deformable Surfaces
(The Eurographics Association, 2012) Ye, Juntao; Zhao, Jing; Jehee Lee and Paul Kry
The Intersection Contour Minimization (ICM) method [VM06] has been proven to be an effective history-free algorithm for resolving collisions between non-oriented deformable surfaces. In many circumstances, however, surface orientation information are often implied in the context. Being completely blind to such information in the ICM method often leads to unexpected result: either failure or slow convergence in certain intersection config- urations. By introducing the concept of ''repulsive normal'' into ICM, many of those once-failure configurations can be resolved successfully. Even for those once-successful configurations, repulsive normals usually speed-up the convergence. Moreover, the ICM method that was originally designed for polygonal meshes can actually be adapted to resolve collisions between a polygon mesh and an analytical surface. This paper presents one such extension collisions between a polygon mesh and a capsule.
Learning Motion Controllers with Adaptive Depth Perception
(The Eurographics Association, 2012) Lo, Wan-Yen; Knaus, Claude; Zwicker, Matthias; Jehee Lee and Paul Kry
We present a novel approach to real-time character animation that allows a character to move autonomously based on vision input. By allowing the character to ''see'' the environment directly using depth perception, we can skip the manual design phase of parameterizing the state space in a reinforcement learning framework. In previous work, this is done manually since finding a minimal set of parameters for describing a character's environment is crucial for efficient learning. Learning from raw vision input, however, suffers from the ''curse of dimensionality'', which we avoid by introducing a hierarchical state model and a novel regression algorithm. We demonstrate that our controllers allow a character to navigate and survive in environments containing arbitrarily shaped obstacles, which is hard to achieve with existing reinforcement learning frameworks.
Linear-Time Smoke Animation with Vortex Sheet Meshes
(The Eurographics Association, 2012) Brochu, Tyson; Keeler, Todd; Bridson, Robert; Jehee Lee and Paul Kry
We present the first quality physics-based smoke animation method which runs in time approximately linear in the size of the rendered two-dimensional visual detail. Our fundamental representation is a closed triangle mesh surface dividing space between clear air and a uniformly smoky region, on which we compute vortex sheet dynamics to accurately solve inviscid buoyant flow. We handle arbitrary moving no-stick solid boundaries and by default handle an infinite domain. The simulation itself runs in time linear to the number of triangles thanks to the use of a well-conditioned integral equation treatment together with a Fast Multipole Method for linear-time summations, providing excellent performance. Basic zero-albedo smoke rendering, with embedded solids, is easy to implement for interactive rates, and the mesh output can also serve as an extremely compact and detailed input to more sophisticated volume rendering.
Misconceptions of PD Control in Animation
(The Eurographics Association, 2012) Allen, Brian F.; Faloutsos, Petros; Jehee Lee and Paul Kry
In this paper, we address certain misconceptions that have been perpetuated in the animation practice and research for quite some time related to the proportional-derivative (PD) control of physics-based systems. Because in animation we often think in terms of targeting keyframes, we tend to forget that PD control, in its simple form, has a very specific asymptotic behavior that approaches zero (or an offset) with zero velocity as time approaches infinity. We pay particular attention to the issue of introducing a ''desired'' or ''end'' velocity term in the equation of a proportional-derivative controller, and discuss how this term should be interpreted and how it relates to feedforward control rather than an end derivative problem.
Multi-linear Data-Driven Dynamic Hair Model with Efficient Hair-Body Collision Handling
(The Eurographics Association, 2012) Guan, Peng; Sigal, Leonid; Reznitskaya, Valeria; Hodgins, Jessica K.; Jehee Lee and Paul Kry
We present a data-driven method for learning hair models that enables the creation and animation of many interactive virtual characters in real-time (for gaming, character pre-visualization and design). Our model has a number of properties that make it appealing for interactive applications: (i) it preserves the key dynamic properties of physical simulation at a fraction of the computational cost, (ii) it gives the user continuous interactive control over the hair styles (e.g., lengths) and dynamics (e.g., softness) without requiring re-styling or re-simulation, (iii) it deals with hair-body collisions explicitly using optimization in the low-dimensional reduced space, (iv) it allows modeling of external phenomena (e.g., wind). Our method builds on the recent success of reduced models for clothing and fluid simulation, but extends them in a number of significant ways. We model motion of hair in a conditional reduced sub-space, where the hair basis vectors, which encode dynamics, are linear functions of userspecified hair parameters. We formulate collision handling as an optimization in this reduced sub-space using fast iterative least squares. We demonstrate our method by building dynamic, user-controlled models of hair styles.
Occlusion-free Camera Control for Multiple Targets
(The Eurographics Association, 2012) Christie, Marc; Normand, Jean-Marie; Olivier, Patrick; Jehee Lee and Paul Kry
Maintaining the visibility of target objects is a fundamental problem in automatic camera control for 3D graphics applications. Practical real-time camera control algorithms generally only incorporate mechanisms for the evaluation of the visibility of target objects from a single viewpoint, and idealize the geometric complexity of target objects. Drawing on work in soft shadow generation, we perform low resolution projections, from target objects to rapidly compute their visibility for a sample of locations around the current camera position. This computation is extended to aggregate visibility in a temporal window to improve camera stability in the face of partial and sudden onset occlusion. To capture the full spatial extent of target objects we use a stochastic approximation of their surface area. Our implementation is the first practical occlusion-free real-time camera control framework for multiple target objects. The result is a robust component that can be integrated to any virtual camera control system that requires the precise computation of visibility for multiple targets.
Precomputed Motion Maps for Unstructured Motion Capture
(The Eurographics Association, 2012) Mahmudi, Mentar; Kallmann, Marcelo; Jehee Lee and Paul Kry
We present in this paper a solution for extracting high-quality motions from unstructured motion capture databases at interactive rates. The proposed solution is based on automatically-built motion graphs, and offers two key contributions. First, we show how precomputed expansion trees (or motion maps) coupled with new heuristics and backtracking techniques are able to significantly improve the time taken to search for motions satisfying user constraints. Second, we show that when feature-based transitions are employed for constructing the underlying motion graph, the connectivity of motion maps is greatly increased, allowing the overall method to perform search and synthesis at interactive frame rates. We demonstrate the effectiveness of our approach with the problem of extracting path-following motions around obstacles from a motion graph structure at interactive performances.
Principal Geodesic Dynamics
(The Eurographics Association, 2012) Tournier, Maxime; Reveret, Lionel; Jehee Lee and Paul Kry
This paper presents a new integration of a data-driven approach using dimension reduction and a physicallybased simulation for real-time character animation. We exploit Lie group statistical analysis techniques (Principal Geodesic Analysis, PGA) to approximate the pose manifold of a motion capture sequence by a reduced set of pose geodesics. We integrate this kinematic parametrization into a physically-based animation approach of virtual characters, by using the PGA-reduced parametrization directly as generalized coordinates of a Lagrangian formulation of mechanics. In order to achieve real-time without sacrificing stability, we derive an explicit time integrator by approximating existing variational integrators. Finally, we test our approach in task-space motion control. By formulating both physical simulation and inverse kinematics time stepping schemes as two quadratic programs, we propose a features-based control algorithm that interpolates between the two metrics. This allows for an intuitive trade-off between realistic physical simulation and controllable kinematic manipulation.
Quaternion Space Sparse Decomposition for Motion Compression and Retrieval
(The Eurographics Association, 2012) Zhu, Mingyang; Sun, Huaijiang; Deng, Zhigang; Jehee Lee and Paul Kry
Quaternion has become one of the most widely used representations for rotational transformations in 3D graphics for decades. Due to the sparse nature of human motion in both the spatial domain and the temporal domain, an unexplored yet challenging research problem is how to directly represent intrinsically sparse human motion data in quaternion space. In this paper we propose a novel quaternion space sparse decomposition (QSSD) model that decomposes human rotational motion data into two meaningful parts (namely, the dictionary part and the weight part) with the sparseness constraint on the weight part. Specifically, a linear combination (addition) operation in Euclidean space is equivalently modeled as a quaternion multiplication operation, and the weight of linear combination is modeled as a power operation on quaternion. Besides validations of the robustness, convergence, and accuracy of the QSSD model, we also demonstrate its two selected applications: human motion data compression and content-based human motion retrieval. Through numerous experiments and quantitative comparisons, we demonstrate that the QSSD-based approaches can soundly outperform existing state-of-the-art human motion compression and retrieval approaches.
Real-Time Example-Based Elastic Deformation
(The Eurographics Association, 2012) Koyama, Yuki; Takayama, Kenshi; Umetani, Nobuyuki; Igarashi, Takeo; Jehee Lee and Paul Kry
We present an example-based elastic deformation method that runs in real time. Example-based elastic deformation was originally presented by Martin et al. [MTGG11], where an artist can intuitively control elastic material behaviors by simply giving example poses. Their FEM-based approach is, however, computationally expensive requiring nonlinear optimization, which hinders its use in real-time applications such as games. Our contribution is to formulate an analogous concept using the shape matching framework, which is fast, robust, and easy to implement. The key observation is that each overlapping local region's right stretch tensor obtained by polar decomposition is a natural choice for a deformation descriptor. This descriptor allows us to represent the pose space as a linear blending of examples. At each time step, the current deformation descriptor is linearly projected onto the example manifold, and then used to modify the rest shape of each local region when computing goal positions. Our approach is two orders of magnitude faster than Martin et al.'s approach while producing comparable example-based elastic deformations.

Browse

Browsing SCA 12: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "Animation"

Results Per Page

Sort Options