SCA: Eurographics/SIGGRAPH Symposium on Computer Animation

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A 2-Stages Locomotion Planner for Digital Actors
(The Eurographics Association, 2003) Pettré, Julien; Laumond, Jean-Paul; Siméon, Thierry; D. Breen and M. Lin
This paper presents a solution to the locomotion planning problem for digital actors. The solution is based both on probabilistic motion planning and on motion capture blending and warping. The paper describes the various components of our solution, from the first path planning to the last animation step. An example illustrates the progression of the animation construction all along the presentation.
Accurate Simulation of Wound Healing and Skin Deformation
(The Eurographics Association, 2016) Feess, Stefan; Kurfiss, Kathrin; Fedkiw, Ronald P.; Michels, Dominik L.; Ladislav Kavan and Chris Wojtan
We devise a method for the accurate simulation of wound healing and skin deformation. This is based on adequate formulations modeling the underlying biological processes. Cell movements and proliferation are described by a biochemical model whereas a biomechanical model covers effects like wound contraction and the influence of the healing process on the surrounding skin. The resulting simulation framework is very efficient and can be used with realistic input parameters like those measured in biochemistry and biophysics. The accurate behavior of our approach is shown by reproducing regenerative healing processes as well as specific effects such as anisotropic wound contraction, scarring and scab formation. Its efficiency and robustness is illustrated on a broad spectrum of complex examples.
Accurate Surface Embedding for Higher Order Finite Elements
(ACM SIGGRAPH / Eurographics Association, 2013) Suwelack, Stefan; Lukarski, Dimitar; Heuveline, Vincent; Dillmann, Rüdiger; Speidel, Stefanie; Theodore Kim and Robert Sumner
In this paper we present a novel approach to efficiently simulate the deformation of highly detailed meshes using higher order finite elements (FE). An efficient algorithm based on non-linear optimization is proposed in order to find the closest point in the curved computational FE mesh for each surface vertex. In order to extrapolate deformations to surface points outside the FE mesh, we introduce a mapping scheme that generates smooth surface deformations and preserves local shape even for low-resolution computational meshes. The mapping is constructed by representing each surface vertex in terms of points on the computational mesh and its distance to the FE mesh in normal direction. A numerical analysis shows that the mapping can be robustly constructed using the proposed non-linear optimization technique. Furthermore it is demonstrated that the numerical complexity of the mapping scheme is linear in the number of surface nodes and independent of the size of the coarse computational mesh.
Accurate Tangential Velocities For Solid Fluid Coupling
(ACM SIGGRAPH / Eurographics Association, 2009) Robinson-Mosher, Avi; English, R. Elliot; Fedkiw, Ronald; Eitan Grinspun and Jessica Hodgins
We propose a novel method for obtaining more accurate tangential velocities for solid fluid coupling. Our method works for both rigid and deformable objects as well as both volumetric objects and thin shells. The fluid can be either one phase such as smoke or two phase such as water with a free surface. The coupling between the solid and the fluid can either be one-way with kinematic solids or fully two-way coupled. The only previous scheme that was general enough to handle both two-way coupling and thin shells required a mass lumping strategy that did not allow for freely flowing tangential velocities. Similar to that previous work, our method prevents leaking of fluid across a thin shell, however unlike that work our method does not couple the tangential velocities in any fashion, allowing for the proper slip independently on each side of the body. Moreover, since it accurately and directly treats the tangential velocity, it does not rely on grid refinement to obtain a reasonable solution. Therefore, it gives a highly improved result on coarse meshes.
Accurate Viscous Free Surfaces for Buckling, Coiling, and Rotating Liquids
(The Eurographics Association, 2008) Batty, Christopher; Bridson, Robert; Markus Gross and Doug James
We present a fully implicit Eulerian technique for simulating free surface viscous liquids which eliminates artifacts in previous approaches, efficiently supports variable viscosity, and allows the simulation of more compelling viscous behaviour than previously achieved in graphics. Our method exploits a variational principle which automatically enforces the complex boundary condition on the shear stress at the free surface, while giving rise to a simple discretization with a symmetric positive definite linear system. We demonstrate examples of our technique capturing realistic buckling, folding and coiling behavior. In addition, we explain how to handle domains whose boundary comprises both ghost fluid Dirichlet and variational Neumann parts, allowing correct behaviour at free surfaces and solid walls for both our viscous solve and the variational pressure projection of Batty et al. [BBB07].
Achieving Good Connectivity in Motion Graphs
(The Eurographics Association, 2008) Zhao, Liming; Safonova, Alla; Markus Gross and Doug James
Motion graphs provide users with a simple yet powerful way to synthesize human motions. While motion graphbased synthesis has been widely successful, the quality of the generatedmotion depends largely on the connectivity of the graph and the quality of transitions in it. However, achieving both of these criteria simultaneously in motion graphs is difficult. Good connectivity requires transitions between less similar poses, while good motion quality results only when transitions happen between very similar poses. This paper introduces a new method for building motion graphs. The method first builds a set of interpolated motion clips, which contain many more similar poses than the original dataset. Using this set, the method then constructs a motion graph and reduces its size by minimizing the number of interpolated poses present in the graph. The outcome of the algorithm is a motion graph called a well-connected motion graph with very good connectivity and only smooth transitions. Our experimental results show that well-connected motion graphs outperform standardmotion graphs across a number of measures, result in very good motion quality, allow for high responsiveness when used for interactive control, and even do not require post-processing of the synthesizedmotions
ACT2G: Attention-based Contrastive Learning for Text-to-Gesture Generation
(ACM Association for Computing Machinery, 2023) Teshima, Hitoshi; Wake, Naoki; Thomas, Diego; Nakashima, Yuta; Kawasaki, Hiroshi; Ikeuchi, Katsushi; Wang, Huamin; Ye, Yuting; Victor Zordan
Recent increase of remote-work, online meeting and tele-operation task makes people find that gesture for avatars and communication robots is more important than we have thought. It is one of the key factors to achieve smooth and natural communication between humans and AI systems and has been intensively researched. Current gesture generation methods are mostly based on deep neural network using text, audio and other information as the input, however, they generate gestures mainly based on audio, which is called a beat gesture. Although the ratio of the beat gesture is more than 70% of actual human gestures, content based gestures sometimes play an important role to make avatars more realistic and human-like. In this paper, we propose a attention-based contrastive learning for text-to-gesture (ACT2G), where generated gestures represent content of the text by estimating attention weight for each word from the input text. In the method, since text and gesture features calculated by the attention weight are mapped to the same latent space by contrastive learning, once text is given as input, the network outputs a feature vector which can be used to generate gestures related to the content. User study confirmed that the gestures generated by ACT2G were better than existing methods. In addition, it was demonstrated that wide variation of gestures were generated from the same text by changing attention weights by creators.
Action Capture with Accelerometers
(The Eurographics Association, 2008) Slyper, Ronit; Hodgins, Jessica; Markus Gross and Doug James
We create a performance animation system that leverages the power of low-cost accelerometers, readily available motion capture databases, and construction techniques from e-textiles. Our system, built with only off-theshelf parts, consists of five accelerometers sewn into a comfortable shirt that streams data to a computer. The accelerometer readings are continuously matched against accelerations computed from existing motion capture data, and an avatar is animated with the closest match. We evaluate our system visually and using simultaneous motion and accelerometer capture.
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.
Adaptive Deformations with Fast Tight Bounds
(The Eurographics Association, 2007) Otaduy, Miguel A.; Germann, Daniel; Redon, Stephane; Gross, Markus; Dimitris Metaxas and Jovan Popovic
Simulation of deformations and collision detection are two highly intertwined problems that are often treated sepa- rately. This is especially true in existing elegant adaptive simulation techniques, where standard collision detection algorithms cannot leverage the adaptively selected degrees of freedom.We propose a seamless integration of multi- grid algorithms and collision detection that identifies boundary conditions while inherently exploiting adaptivity. We realize this integration through multiscale bounding hierarchies, a novel unified hierarchical representation, together with an adaptive multigrid algorithm for irregular meshes and an adaptivity-aware hierarchical collision detection algorithm. Our solution produces detailed deformations with adapted computational cost, but it also enables robust interactive simulation of self-colliding deformable objects with high-resolution surfaces.
Adaptive Rigidification of Discrete Shells
(ACM Association for Computing Machinery, 2023) Mercier-Aubin, Alexandre; Kry, Paul G.; Wang, Huamin; Ye, Yuting; Victor Zordan
We present a method to improve the computation time of thin shell simulations by using adaptive rigidification to reduce the number of degrees of freedom. Our method uses a discretization independent metric for bending rates, and we derive a membrane strain rate to curvature rate equivalence that permits the use of a common threshold. To improve accuracy, we enhance the elastification oracle by considering both membrane and bending deformation to determine when to rigidify or elastify. Furthermore, we explore different approaches that are compatible with the previous work on adaptive rigidifcation and enhance the accuracy of the elastification on new contacts without increasing the computational overhead. Additionally, we propose a scaling approach that reduces the conditioning issues that arise from mixing rigid and elastic bodies in the same model.
Adaptive Tetrahedral Meshes for Brittle Fracture Simulation
(The Eurographics Association, 2014) Koschier, Dan; Lipponer, Sebastian; Bender, Jan; Vladlen Koltun and Eftychios Sifakis
We present a method for the adaptive simulation of brittle fracture of solid objects based on a novel reversible tetrahedral mesh refinement scheme. The refinement scheme preserves the quality of the input mesh to a large extent, it is solely based on topological operations, and does not alter the boundary, i.e. any geometric feature. Our fracture algorithm successively performs a stress analysis and increases the resolution of the input mesh in regions of high tensile stress. This results in an accurate location of crack origins without the need of a general high resolution mesh which would cause high computational costs throughout the whole simulation. A crack is initiated when the maximum tensile stress exceeds the material strength. The introduced algorithm then proceeds by iteratively recomputing the changed stress state and creating further cracks. Our approach can generate multiple cracks from a single impact, but effectively avoids shattering artifacts. Once the tensile stress decreases, the mesh refinement is reversed to increase the performance of the simulation. We demonstrate that our adaptive method is robust, scalable and computes highly realistic fracture results.
An Adaptive Virtual Node Algorithm with Robust Mesh Cutting
(The Eurographics Association, 2014) Wang, Yuting; Jiang, Chenfanfu; Schroeder, Craig; Teran, Joseph; Vladlen Koltun and Eftychios Sifakis
We present a novel virtual node algorithm (VNA) for changing tetrahedron mesh topology to represent arbitrary cutting triangulated surfaces. Our approach addresses a number of shortcomings in the original VNA of [MBF04]. First, we generalize the VNA so that cuts can pass through tetrahedron mesh vertices and lie on mesh edges and faces. The original algorithm did not make sense for these cases and required often ambiguous perturbation of the cutting surface to avoid them. Second, we develop an adaptive approach to the definition of embedded material used for element duplication. The original algorithm could only handle a limited number of configurations which restricted cut surfaces to have curvature at the scale of the tetrahedron elements. Our adaptive approach allows for cut surfaces with curvatures independent of the embedding tetrahedron mesh resolution. Finally, we present a novel, provably-robust floating point mesh intersection routine that accurately registers triangulated surface cuts against the background tetrahedron mesh without the need for exact arithmetic.
Adaptive Wisp Tree - a multiresolution control structure for simulating dynamic clustering in hair motion
(The Eurographics Association, 2003) Bertails, F.; Kim, T-Y.; Cani, M-P.; Neumann, U.; D. Breen and M. Lin
Realistic animation of long human hair is difficult due to the number of hair strands and to the complexity of their interactions. Existing methods remain limited to smooth, uniform, and relatively simple hair motion. We present a powerful adaptive approach to modeling dynamic clustering behavior that characterizes complex long-hair motion. The Adaptive Wisp Tree (AWT) is a novel control structure that approximates the large-scale coherent motion of hair clusters as well as small-scaled variation of individual hair strands. The AWT also aids computation efficiency by identifying regions where visible hair motions are likely to occur. The AWT is coupled with a multiresolution geometry used to define the initial hair model. This combined system produces stable animations that exhibit the natural effects of clustering and mutual hair interaction. Our results show that the method is applicable to a wide variety of hair styles.
ADMM ⊇ Projective Dynamics: Fast Simulation of General Constitutive Models
(The Eurographics Association, 2016) Narain, Rahul; Overby, Matthew; Brown, George E.; Ladislav Kavan and Chris Wojtan
We apply the alternating direction method of multipliers (ADMM) optimization algorithm to implicit time integration of elastic bodies, and show that the resulting method closely relates to the recently proposed projective dynamics algorithm. However, as ADMM is a general-purpose optimization algorithm applicable to a broad range of objective functions, it permits the use of nonlinear constitutive models and hard constraints while retaining the speed, parallelizability, and robustness of projective dynamics. We demonstrate these benefits on several examples that include cloth, collisions, and volumetric deformable bodies with nonlinear elasticity.
Advected Textures
(The Eurographics Association, 2003) Neyret, Fabrice; D. Breen and M. Lin
Game and special effects artists like to rely on textures (image or procedural) to specify the details of surface aspect. In this paper, we address the problem of applying textures to animated fluids. The purpose is to allow artists to increase the details of flowing water, foam, lava, mud, flames, cloud layers, etc. Our first contribution is a new algorithm for advecting textures, which compromises between two contradictory requirements: continuity in space and time and preservation of statistical texture properties. It consist of combining layers of advected (periodically regenerated) parameterizations according to a criterion based on the local accumulated deformation. To correctly achieve this combination, we introduce a way of blending procedural textures while avoiding classical interpolation artifacts. Lastly, we propose a scheme to add and control small scale texture animation amplifying the low resolution simulation. Our results illustrate how these three contributions solve the major visual flaws of textured fluids.
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.
Aesthetic Edits For Character Animation
(The Eurographics Association, 2003) Neff, Michael; Fiume, Eugene; D. Breen and M. Lin
The utility of an interactive tool can be measured by how pervasively it is embedded into a user's work flow. Tools for artists additionally must provide an appropriate level of control over expressive aspects of their work while suppressing unwanted intrusions due to details that are, for the moment, unnecessary. Our focus is on tools that target editing the expressive aspects of character motion. These tools allow animators to work in a way that is more expedient than modifying low-level details, and offers finer control than high level, directorial approaches. To illustrate this approach, we present three such tools, one for varying timing (succession), and two for varying motion shape (amplitude and extent). Succession editing allows the animator to vary the activation times of the joints in the motion. Amplitude editing allows the animator to vary the joint ranges covered during a motion. Extent editing allows an animator to vary how fully a character occupies space during a movement - using space freely or keeping the movement close to his body. We argue that such editing tools can be fully embedded in the workflow of character animators. We present a general animation system in which these and other edits can be defined programmatically. Working in a general pose or keyframe framework, either kinematic or dynamic motion can be generated. This system is extensible to include an arbitrary set of movement edits.
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.
Animal gaits from video
(The Eurographics Association, 2004) Favreau, Laurent; Reveret, Lionel; Depraz, Christine; Cani, Marie-Paule; R. Boulic and D. K. Pai
We present a method for animating 3D models of animals from existing live video sequences such as wild life documentaries. Videos are first segmented into binary images on which Principal Component Analysis (PCA) is applied. The time-varying coordinates of the images in the PCA space are then used to generate 3D animation. This is done through interpolation with Radial Basis Functions (RBF) of 3D pose examples associated with a small set of key-images extracted from the video. In addition to this processing pipeline, our main contributions are: an automatic method for selecting the best set of key-images for which the designer will need to provide 3D pose examples. This method saves user time and effort since there is no more need for manual selection within the video and then trials and errors in the choice of key-images and 3D pose examples. As another contribution, we propose a simple algorithm based on PCA images to resolve 3D pose prediction ambiguities. These ambiguities are inherent to many animal gaits when only monocular view is available. The method is first evaluated on sequences of synthetic images of animal gaits, for which full 3D data is available. We achieve a good quality reconstruction of the input 3D motion from a single video sequence of its 2D rendering. We then illustrate the method by reconstructing animal gaits from live video of wild life documentaries. Key words: Animation from Motion/Video Data, Interpolation Keyframing, Intuitive Interfaces for Animation.

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