Showing papers in "Computer Animation and Virtual Worlds in 2005"

Mixing virtual and real scenes in the site of ancient Pompeii

Abstract: This paper presents an innovative 3D reconstruction of ancient fresco paintings through the real-time revival of their fauna and flora, featuring groups of virtual animated characters with artificial-life dramaturgical behaviours in an immersive, fully mobile augmented reality (AR) environment. The main goal is to push the limits of current AR and virtual storytelling technologies and to explore the processes of mixed narrative design of fictional spaces (e.g. fresco paintings) where visitors can experience a high degree of realistic immersion. Based on a captured/real-time video sequence of the real scene in a video-see-through HMD set-up, these scenes are enhanced by the seamless accurate real-time registration and 3D rendering of realistic complete simulations of virtual flora and fauna (virtual humans and plants) in a real-time storytelling scenario-based environment. Thus the visitor of the ancient site is presented with an immersive and innovative multi-sensory interactive trip to the past

Natural head motion synthesis driven by acoustic prosodic features

Abstract: Natural head motion is important to realistic facial animation and engaging human–computer interactions. In this paper, we present a novel data-driven approach to synthesize appropriate head motion by sampling from trained hidden markov models (HMMs). First, while an actress recited a corpus specifically designed to elicit various emotions, her 3D head motion was captured and further processed to construct a head motion database that included synchronized speech information. Then, an HMM for each discrete head motion representation (derived directly from data using vector quantization) was created by using acoustic prosodic features derived from speech. Finally, first-order Markov models and interpolation techniques were used to smooth the synthesized sequence. Our comparison experiments and novel synthesis results show that synthesized head motions follow the temporal dynamic behavior of real human subjects. Copyright © 2005 John Wiley & Sons, Ltd.

An augmented reality system to guide radio-frequency tumour ablation

Abstract: Radio-frequency ablation is a difficult operative task that requires a precise needle positioning in the centre of the pathology. This article presents an augmented reality system for hepatic therapy guidance that superimposes in real-time 3D reconstructions (from CT acquisition) and a virtual model of the needle on external views of a patient. The superimposition of reconstructed models is performed with a 3D/2D registration based on radio-opaque markers stuck on to the patient's skin. The characteristics of the problem (accuracy, robustness and time processing) led us to develop automatic procedures to extract and match the markers and to track the needle in real time. Experimental studies confirmed that our algorithms are robust and reliable. Preliminary experiments conducted on a human abdomen phantom showed that our system is highly accurate (needle positioning error within 3 mm) and enables the surgeon to reach a target in less than 1 minute on average. Our next step will be to perform an in vivo evaluation. Copyright © 2005 John Wiley & Sons, Ltd.

Psychological model for animating crowded pedestrians

Abstract: This paper proposes a psychological model for simulating pedestrian behaviors in a crowded space. Our decision-making scheme controls plausible avoidance behavior depending on the positional relations among surrounding persons, on the basis of a two-stage personal space and a virtual memory structure as proposed in social psychology. Our system determines pedestrian walking speed with the crowd density to imitate the measured data in urban engineering, and automatically generates plausible motions of the individual pedestrian by composing a locomotion graph with motion capture data. Our approach based on psychology and a variety of actual measurements can increase the accuracy of simulation at both the micro and macro levels. Copyright # 2005 John Wiley & Sons, Ltd.

From dance notation to human animation: The LabanDancer project

Abstract: Symbolic systems such as Labanotation for notating dance and choreography provide a critical tool for the preservation of cultural heritage in what once was considered an ‘illiterate’ art form. While the goals of such notation systems are laudable, the unfortunate reality is that most dancers and choreographers cannot read or write the notation; that is, they are loath to take the considerable effort to learn a rich, but complex methodology. To make Labanotation scores more accessible the LabanDancer system has been developed to translate Labanotation scores recorded in the LabanWriter editor into 3-d human figure animations. A major challenge in the development of this translator has been to find approaches that are general enough to create reasonable animations for a wide variety of different movements. Any translator must also take account of the context of a movement since this can affect the interpretation of the Labanotation scores. Copyright © 2005 John Wiley & Sons, Ltd.

Real‐time simulation of watery paint

Abstract: Existing work on applications for thin watery paint is mostly focused on automatic generation of painterly-style images from input images, ignoring the fact that painting is a process that intuitively should be interactive. Efforts to create real-time interactive systems are limited to a single paint medium and results often suffer from a trade-off between real-timeness and simulation complexity. We report on the design of a new system that allows the real-time, interactive creation of images with thin watery paint. We mainly target the simulation of watercolor, but the system is also capable of simulating gouache and Oriental black ink. The motion of paint is governed by both physically based and heuristic rules in a layered canvas design. A final image is rendered by optically composing the layers using the Kubelka–Munk diffuse reflectance model. All algorithms that participate in the dynamics phase and the rendering phase of the simulation are implemented on graphics hardware. Images made with the system contain the typical effects that can be recognized in images produced with real thin paint, like the dark-edge effect, watercolor glazing, wet-on-wet painting and the use of different pigment types. Copyright © 2005 John Wiley & Sons, Ltd.

Implicit midpoint integration and adaptive damping for efficient cloth simulation

Abstract: Implicit integration methods have contributed to large performance enhancements in the field of simulation of particle-system mechanical models. While Backward Euler and BDF-2 methods are now widely used for cloth simulation applications, the Implicit Midpoint method is often overlooked, because of its poor stability properties. It is however as simple to implement as Backward Euler, and offers significantly better accuracy and even shorter computation times. Starting with a study of the stability properties of these integration methods, we will find out how moderate viscous damping may efficiently restore stability of Implicit Midpoint integration method. An extension is also proposed for BDF-2 methods. Comparative examples demonstrate the benefits of this approach. Copyright © 2005 John Wiley & Sons, Ltd.

Animating reactive motion using momentum-based inverse kinematics

Abstract: Interactive generation of reactive motions for virtual humans as they are hit, pushed and pulled are very important to many applications, such as computer games. In this paper, we propose a new method to simulate reactive motions during arbitrary bipedal activities, such as standing, walking or running. It is based on momentum based inverse kinematics and motion blending. When generating the animation, the user first imports the primary motion to which the perturbation is to be applied to. According to the condition of the impact, the system selects a reactive motion from the database of pre-captured stepping and reactive motions. It then blends the selected motion into the primary motion using momentum-based inverse kinematics. Since the reactive motions can be edited in real-time, the criteria for motion search can be much relaxed than previous methods, and therefore, the computational cost for motion search can be reduced. Using our method, it is possible to generate reactive motions by applying external perturbations to the characters at arbitrary moment while they are performing some actions. Copyright # 2005 John Wiley & Sons, Ltd.

From dance notation to human animation: The LabanDancer project: Motion Capture and Retrieval

Abstract: Symbolic systems such as Labanotation for notating dance and choreography provide a critical tool for the preservation of cultural heritage in what once was considered an ‘illiterate’ art form. While the goals of such notation systems are laudable, the unfortunate reality is that most dancers and choreographers cannot read or write the notation; that is, they are loath to take the considerable effort to learn a rich, but complex methodology. To make Labanotation scores more accessible the LabanDancer system has been developed to translate Labanotation scores recorded in the LabanWriter editor into 3-d human figure animations. A major challenge in the development of this translator has been to find approaches that are general enough to create reasonable animations for a wide variety of different movements. Any translator must also take account of the context of a movement since this can affect the interpretation of the Labanotation scores. Copyright © 2005 John Wiley & Sons, Ltd.

Interactive venation-based leaf shape modeling

Abstract: We describe a representation for tree leaves and an interactive modeling system for creating realistic close-up images of leaf clusters. The planar outline of the leaf and the larger members of its venation system are strong factors in the recognition of plant species and as such are essential to realistic imaging. The larger veins also play a major biological role in determining the leaf surface shape and it is this role that we mimic in the shape modeling discussed in this paper. The proposed representation uses a model of a leaf consisting of a three-dimensional skeleton formed by its larger veins and a surface membrane representing the leaf lamina that spans the void between the veins. The veins play two roles. They can be interactively modified to create the 3-D shape of the leaf model. They also provide for realistic light and shadow effects when rendered as generalized cylinders using measured width parameters. The representation consists of two coupled data structures, a tree data structure of veins for the leaf skeleton and an unstructured triangular mesh for the leaf membrane. The skeleton is modified by the user of the modeling system, and the membrane mesh is a surface mesh that follows the skeleton shape computed using harmonic interpolation. Copyright © 2005 John Wiley & Sons, Ltd.

Motion retrieval based on movement notation language

Abstract: With the increased availability of motion capture data, the volume of motion library grows so large that it is difficult for animators to manually browse the dataset to search desired motions for reuse. To address this issue, we implement a framework, which allows the user to retrieve motions via Labanotation. For each motion clip in the library, we generate a corresponding Labanotation sequence as additional motion property. A similarity metric for Labanotation sequences is proposed and used to search the motions that have similar Laban descriptions. Our search algorithm is able to retrieve motion segments that only match part of the query Laban sequence. Then based on dynamic programming, these segments are stitched together to form a smooth output motion that is in an optimal sense of matching query Laban sequence. Experimental results demonstrate our method could effectively improve the utilization of motion data. Copyright © 2005 John Wiley & Sons, Ltd.

Mixing virtual and real scenes in the site of ancient Pompeii: Research Articles

Abstract: This paper presents an innovative 3D reconstruction of ancient fresco paintings through the real-time revival of their fauna and flora, featuring groups of virtual animated characters with artificial-life dramaturgical behaviours in an immersive, fully mobile augmented reality (AR) environment. The main goal is to push the limits of current AR and virtual storytelling technologies and to explore the processes of mixed narrative design of fictional spaces (e.g. fresco paintings) where visitors can experience a high degree of realistic immersion. Based on a captured/real-time video sequence of the real scene in a video-see-through HMD set-up, these scenes are enhanced by the seamless accurate real-time registration and 3D rendering of realistic complete simulations of virtual flora and fauna (virtual humans and plants) in a real-time storytelling scenario-based environment. Thus the visitor of the ancient site is presented with an immersive and innovative multi-sensory interactive trip to the past. Copyright © 2005 John Wiley & Sons, Ltd.

Real-time meshless deformation

Abstract: In this paper, we articulate a meshless computational paradigm for the effective modeling, accurate physical simulation, and real-time animation of point-sampled solid objects. Both the interior and the boundary geometry of our volumetric object representation only consist of points, further extending the powerful and popular method of point-sampled surfaces to the volumetric setting. We build the point-based physical model upon continuum mechanics, which affords to effectively model the dynamic elastic behavior of point-based volumetric objects. When only surface samples are provided, our prototype system first generates both interior volumetric points and a volumetric distance field with octree structure. The physics of these volumetric points in a solid interior are simulated using the Meshless Moving Least Squares (MLS) shape functions. In sharp contrast to the traditional finite element method (FEM), the meshless property of our new technique expedites the accurate representation and precise simulation of the underlying discrete model, without the need of domain meshing. In order to achieve real-time simulations, we utilize the warped modal analysis method that is locally linear in nature but globally warped to account for rotational deformation. The structural simplicity and real-time performance of our meshless simulation framework are ideal for interactive animation and game/movie production. Copyright # 2005 John Wiley & Sons, Ltd.

Entropy-based motion extraction for motion capture animation

Abstract: In this paper, we present a new segmentation solution for extracting motion patterns from motion capture data by searching for critical keyposes in the motion sequence. A rank is established for critical keyposes that identifies the significance of the directional change in motion data. The method is based on entropy metrics, specifically the mutual information measure. Displacement histograms between frames are evaluated and the mutual information metric is employed in order to calculate the inter-frame dependency. The most significant keypose identifies the largest directional change in the motion data. This will have the lowest mutual information level from all the candidate keyposes. Less significant keyposes are then listed with higher mutual information levels. The results show that the method has higher sensitivity in the directional change than methods based on the magnitude of the velocity alone. This method is intended to provide a summary of a motion clip by ranked keyposes, which is highly useful in motion browsing and motion retrieve database system. Copyright © 2005 John Wiley & Sons, Ltd.

An augmented reality system to guide radio-frequency tumour ablation: Research Articles

Abstract: Radio-frequency ablation is a difficult operative task that requires a precise needle positioning in the centre of the pathology. This article presents an augmented reality system for hepatic therapy guidance that superimposes in real-time 3D reconstructions (from CT acquisition) and a virtual model of the needle on external views of a patient. The superimposition of reconstructed models is performed with a 3D/2D registration based on radio-opaque markers stuck on to the patient's skin. The characteristics of the problem (accuracy, robustness and time processing) led us to develop automatic procedures to extract and match the markers and to track the needle in real time. Experimental studies confirmed that our algorithms are robust and reliable. Preliminary experiments conducted on a human abdomen phantom showed that our system is highly accurate (needle positioning error within 3 mm) and enables the surgeon to reach a target in less than 1 minute on average. Our next step will be to perform an in vivo evaluation. Copyright © 2005 John Wiley & Sons, Ltd.

Automated motion synthesis for dancing characters

Abstract: In this paper, we present a technique to automatically synthesize dancing motions for arbitrary songs with dance beats. Our technique is based on analysing a musical tune (can be a song or melody) and synthesizing a motion for the virtual character where the character's movement synchronizes to the musical beats. In order to analyse beats of the tune, we developed a fast algorithm. Our motion synthesis algorithm analyses library of stock motions and generates new sequences of movements that were not described in the library. We show that our motion synthesis algorithm is better than previous dance generation techniques. We also present two algorithms to synchronize dance moves and musical beats: a fast greedy algorithm, and a genetic algorithm. Our experimental results show that we can generate new sequences of dance figures in which the dancer reacts to music and dances in synchronization with the music. Copyright © 2005 John Wiley & Sons, Ltd.

Mesh decomposition using motion information from animation sequences

Abstract: In computer graphics, mesh decomposition is a fundamental problem and it can benefit many applications. In this paper, we propose a novel mesh decomposition algorithm using motion information derived from a given animation sequence. The proposed algorithm first use principal component analysis (PCA) to construct a compact representation of a given animation sequence. Next, from this representation, we derive several motion parameters including motion complexity and similarity. Finally, we decompose a given mesh into sub-meshes using derived motion information and subdivide the triangles along the cutting paths for the smoother borders between the mesh parts. Our experimental results show that this new decomposition scheme can bring the benefit of good compression ratios on animation sequences. Copyright © 2005 John Wiley & Sons, Ltd.

Psychological model for animating crowded pedestrians: Virtual Humans and Social Agents

Abstract: This paper proposes a psychological model for simulating pedestrian behaviors in a crowded space. Our decision-making scheme controls plausible avoidance behavior depending on the positional relations among surrounding persons, on the basis of a two-stage personal space and a virtual memory structure as proposed in social psychology. Our system determines pedestrian walking speed with the crowd density to imitate the measured data in urban engineering, and automatically generates plausible motions of the individual pedestrian by composing a locomotion graph with motion capture data. Our approach based on psychology and a variety of actual measurements can increase the accuracy of simulation at both the micro and macro levels. Copyright © 2005 John Wiley & Sons, Ltd.

Real-time simulation of watery paint: Natural Phenomena and Special Effects

Abstract: Existing work on applications for thin watery paint is mostly focused on automatic generation of painterly-style images from input images, ignoring the fact that painting is a process that intuitively should be interactive. Efforts to create real-time interactive systems are limited to a single paint medium and results often suffer from a trade-off between real-timeness and simulation complexity. We report on the design of a new system that allows the real-time, interactive creation of images with thin watery paint. We mainly target the simulation of watercolor, but the system is also capable of simulating gouache and Oriental black ink. The motion of paint is governed by both physically based and heuristic rules in a layered canvas design. A final image is rendered by optically composing the layers using the Kubelka–Munk diffuse reflectance model. All algorithms that participate in the dynamics phase and the rendering phase of the simulation are implemented on graphics hardware. Images made with the system contain the typical effects that can be recognized in images produced with real thin paint, like the dark-edge effect, watercolor glazing, wet-on-wet painting and the use of different pigment types. Copyright © 2005 John Wiley & Sons, Ltd.

Physically based morphing of point-sampled surfaces

Abstract: This paper presents an innovative method for naturally and smoothly morphing point- sampled surfaces via dynamic meshless simulation on point-sampled surfaces. While most existing literature on shape morphing emphasizes the issue of finding a good correspondence map between two object representations, this research primarily investigates the challenging problem of how to find a smooth, physically-meaningful transition path between two homeomorphic point-set surfaces. We analyze the deformation of surface involved in the morphing process using concepts in differential geometry and continuum mechanics. The morphing paths can be determined by optimizing an energy functional, which characterizes the intrinsic deformation of the surface away from its rest shape. As demonstrated in the examples, our method automatically produces a series of natural and physically-plausible in-between shapes, which greatly alleviates the shrinking, stretching, and self-intersection problems that often occur when linear interpolation is employed for the morphing of two objects. We envision that our new technique will continue to broaden the application scope of point-set surfaces and their dynamic animation. Copyright # 2005 John Wiley & Sons, Ltd.

Mesh morphing using polycube-based cross-parameterization

Abstract: In this paper, we propose a novel mesh morphing approach based on polycubic cross- parameterization. We compose parameterizations over the surfaces of the polycubes whose shape is similar to that of the given meshes. Because the polycubes capture the large-scale features, we can easily preserve the shape of the models, mapping legs to legs, head to head, and so on. For the finer features that are not reflected by the shape of the polycubes, we split the polycubes into matching patches and optimize them to get a low-distortion bijection that satisfies user-prescribed constraints. Our approach works well for meshes with arbitrary genus as long as the polycubes capture this feature and transfers texture seamlessly. We can also build maps with singularities between models with different genus. Copyright # 2005 John Wiley & Sons, Ltd.

Modeling and simulating the deformation of human skeletal muscle based on anatomy and physiology

Abstract: This paper describes the modeling and simulation of the deformation of human skeletal muscle at different structural levels based on sound scientific principles, experimental evidence, and state-of-art muscle anatomy and physiology. The equations of a continuum model of a muscle with realistic architecture, including internal arrangement of muscle fibers and passive structures, and deformation, including activation relations, was developed and solved with the finite element method. The continuum model is used as the basis of a strategy for controlling muscle deformation using activation relations. In order to demonstrate the functionality of the model, it was used to investigate force production and structural changes during contraction of the human tibialis anterior for maximally and submaximally activated muscle behavior. From a comparison with experimental data obtained from ultrasound imaging, we concluded that the modeling and simulation of the continuum based on physiologically meaningful parameters as described in the paper is both an excellent predictor of force production observations and of changes in internal geometry under various test conditions. It is therefore a valuable tool for controlling muscle deformation during movement. Copyright © 2005 John Wiley & Sons, Ltd.

Design and evaluation of Elva: an embodied tour guide in an interactive virtual art gallery

Abstract: The technology of embodied conversational agents provides an attractive approach to achieving natural human—computer interaction if the interaction design is handled sensitively. In view of this, we designed and developed an embodied tour guide, Elva, ‘who’ is able to engage conversationally with users about gallery exhibits and also capable of behaving non-verbally using gesture and facial expression. The research focuses on the attributes of agent autonomy and believability. To achieve autonomy, we present a three-layer architectural design to ensure appropriate coupling between the agent's perception and action. With regard to believability, we utilize the notion of schema to support structured and coherent verbal behaviours. We also pay careful attention to the design of non-verbal interactions that establish social facts within the virtual world. A user study was performed to evaluate user satisfaction and agent believability. Copyright © 2005 John Wiley & Sons, Ltd.

Mapping cityscapes into cyberspace for visualization

Abstract: This work establishes a cyberspace of a real urban area for visiting on the Internet. By registering entire scenes along every street and at many locations, viewers can visually travel around and find their destinations in cyberspace. The issues we discuss here are mapping of a large-scale area to image domains in a small amount of data, and effective display of the captured scenes for various applications. Route Panoramas captured along streets and panoramic views captured at widely opening sites are associated to a city map to provide navigation functions. This paper focuses on the properties of our extended images—route panorama, addressing the archiving process applied to an urban area, an environment developed to transmit image data as streaming media, and display for scene traversing on the WWW in real time. The created cyberspaces of urban areas have broad applications such as city tour, real estate searching, e-commerce, heritage preservation, urban planning and construction, and vehicle navigation. Copyright © 2005 John Wiley & Sons, Ltd.

GPU‐based intrinsic collision detection for deformable surfaces

Abstract: An intrinsic collision detection unit (ICDU) forms the bottom-most layer of a collision detection pipeline. The ICDU performs collision detection and computes collision information for primitive feature pairs of objects in a 3D dynamic environment. A significant amount of time can be spent by the ICDU during the collision detection process. In this paper, we extend the ICDU framework to take advantages of the computational power of programmable graphics processors (GPUs). Some components of the ICDU framework consist of time demanding and fine-grained tasks that can be implemented on GPUs. By employing the framework, collision information can be computed accurately, robustly, and efficiently. Experimental results show that the proposed method greatly improves the performance of the ICDU. A collection buffer is proposed for the future enhancement of GPU-based collision detectors. Copyright © 2005 John Wiley & Sons, Ltd.

Real-time meshless deformation: Collision Detection and Deformable Objects

Abstract: In this paper, we articulate a meshless computational paradigm for the effective modeling, accurate physical simulation, and real-time animation of point-sampled solid objects. Both the interior and the boundary geometry of our volumetric object representation only consist of points, further extending the powerful and popular method of point-sampled surfaces to the volumetric setting. We build the point-based physical model upon continuum mechanics, which affords to effectively model the dynamic elastic behavior of point-based volumetric objects. When only surface samples are provided, our prototype system first generates both interior volumetric points and a volumetric distance field with octree structure. The physics of these volumetric points in a solid interior are simulated using the Meshless Moving Least Squares (MLS) shape functions. In sharp contrast to the traditional finite element method (FEM), the meshless property of our new technique expedites the accurate representation and precise simulation of the underlying discrete model, without the need of domain meshing. In order to achieve real-time simulations, we utilize the warped modal analysis method that is locally linear in nature but globally warped to account for rotational deformation. The structural simplicity and real-time performance of our meshless simulation framework are ideal for interactive animation and game/movie production. Copyright © 2005 John Wiley & Sons, Ltd.

Dynamic modeling and rendering of grass wagging in wind

Abstract: Simulation of dynamic natural scene is one of the most challenging tasks in computer graphics. In this paper, we propose a new approach to dynamic modeling and rendering of grasses wagging in wind. Through length preserving free-form deformation of the 3D skeleton lines of each grass blade and using the alpha test to implement transparent texture mapping, we successfully model grasses of different shapes with rich details. To simulate the real time waggle of grasses, the grasses of a meadow are represented in LOD, while their skeleton lines are dynamically deformed according to some physical models. Simplification technique is also employed to accelerate the collision detection between neighboring grasses. Experiments show that our method can realistically render the animated grass scenes under wind of different speeds and types in real time. Copyright © 2005 John Wiley & Sons, Ltd.

Enhanced auto coloring with hierarchical region matching

Abstract: This paper proposes a Hierarchical Region Matching (HRM) approach for computer-assisted auto coloring. The region-level analysis in traditional 2D animation is expanded into several component levels with a novel hierarchization method. With the hierarchy, various region matching algorithms can be applied from the first/highest to the last/lowest component level. HRM improves the matching accuracy and may deal with matching errors caused by occlusion, thus making the matching more robust, as verified by the results. Copyright © 2005 John Wiley & Sons, Ltd.

Time‐critical animation of deformable solids

Abstract: This article presents a model for handling multi-resolution animation of complex deformable models An octree-based animation and algorithmic tools are introduced to provide real-time interaction on complex objects Some efficient collision detection scheme is also described for deformable models A method is also presented for time-guaranteed mechanical simulation: It allows an automatic tuning of the octree resolution to match some external performance constraints, such as a pre-defined CPU consumption limit Copyright © 2005 John Wiley & Sons, Ltd

Automated motion synthesis for dancing characters: Motion Capture and Retrieval

Abstract: In this paper, we present a technique to automatically synthesize dancing motions for arbitrary songs with dance beats. Our technique is based on analysing a musical tune (can be a song or melody) and synthesizing a motion for the virtual character where the character's movement synchronizes to the musical beats. In order to analyse beats of the tune, we developed a fast algorithm. Our motion synthesis algorithm analyses library of stock motions and generates new sequences of movements that were not described in the library. We show that our motion synthesis algorithm is better than previous dance generation techniques. We also present two algorithms to synchronize dance moves and musical beats: a fast greedy algorithm, and a genetic algorithm. Our experimental results show that we can generate new sequences of dance figures in which the dancer reacts to music and dances in synchronization with the music. Copyright © 2005 John Wiley & Sons, Ltd.