Showing papers in "Computer Animation and Virtual Worlds in 2008"

A survey of mobile and wireless technologies for augmented reality systems

Abstract: Recent advances in hardware and software for mobile computing have enabled a new breed of mobile augmented reality (AR) systems and applications. A new breed of computing called ‘augmented ubiquitous computing’ has resulted from the convergence of wearable computing, wireless networking, and mobile AR interfaces. In this paper, we provide a survey of different mobile and wireless technologies and how they have impact AR. Our goal is to place them into different categories so that it becomes easier to understand the state of art and to help identify new directions of research. Copyright © 2008 John Wiley & Sons, Ltd.

Agent-based human behavior modeling for crowd simulation

Abstract: Human crowd is a fascinating social phenomenon in nature. This paper presents our work on designing behavior model for virtual humans in a crowd simulation under normal-life and emergency situations. Our model adopts an agent-based approach and employs a layered framework to reflect the natural pattern of human-like decision making process, which generally involves a person's awareness of the situation and consequent changes on the internal attributes. The social group and crowd-related behaviors are modeled according to the findings and theories observed from social psychology (e.g., social attachment theory). By integrating our model into an agent execution process, each individual agent can response differently to the perceived environment and make realistic behavioral decisions based on various physiological, emotional, and social group attributes. To demonstrate the effectiveness of our model, a case study has been conducted, which shows that realistic human behaviors can be generated at both individual and group level. Copyright © 2008 John Wiley & Sons, Ltd.

Simulation of ultrasound guided needle puncture using patient specific data with 3D textures and volume haptics

Abstract: We present an integrated system for training ultrasound (US) guided needle puncture. Our aim is to provide a validated training tool for interventional radiology (IR) that uses actual patient data. IR procedures are highly reliant on the sense of touch and so haptic hardware is an important part of our solution. A hybrid surface-volume haptic rendering of an US transducer is proposed to constrain the device to remain outside the bony structures when scanning the patient's skin. A volume haptic model is proposed that implements an effective model of needle puncture. Force measurements have been made on real tissue and the resulting data is incorporated into the model. The other input data required is a computed tomography (CT) scan of the patient that is used to create the patient specific models. It is also the data source for a novel simulation of a virtual US scanner, which is used to guide the needle to the correct location. Copyright © 2007 John Wiley & Sons, Ltd.

Analytical inverse kinematics with body posture control

Abstract: This paper presents a novel whole-body analytical inverse kinematics (IK) method integrating collision avoidance and customizable body control for animating reaching tasks in real-time. Whole-body control is achieved with the interpolation of pre-designed key body postures, which are organized as a function of the direction to the goal to be reached. Arm postures are computed by the analytical IK solution for human-like arms and legs, extended with a new simple search method for achieving postures avoiding joint limits and collisions. In addition, a new IK resolution is presented that directly solves for joints parameterized in the swing-and-twist decomposition. The overall method is simple to implement, fast, and accurate, and therefore suitable for interactive applications controlling the hands of characters. The source code of the IK implementation is provided. Copyright © 2007 John Wiley & Sons, Ltd.

Emulating human perception of motion similarity

Abstract: Evaluating the similarity of motions is useful for motion retrieval, motion blending, and performance analysis of dancers and athletes. Euclidean distance between corresponding joints has been widely adopted in measuring similarity of postures and hence motions. However, such a measure does not necessarily conform to the human perception of motion similarity. In this paper, we propose a new similarity measure based on machine learning techniques. We make use of the results of questionnaires from subjects answering whether arbitrary pairs of motions appear similar or not. Using the relative distance between the joints as the basic features, we train the system to compute the similarity of arbitrary pair of motions. Experimental results show that our method outperforms methods based on Euclidean distance between corresponding joints. Our method is applicable to content-based motion retrieval of human motion for large-scale database systems. It is also applicable to e-Learning systems which automatically evaluates the performance of dancers and athletes by comparing the subjects' motions with those by experts. Copyright © 2008 John Wiley & Sons, Ltd.

Surface matching with salient keypoints in geodesic scale space

Abstract: This paper develops a new salient keypoints-based shape description which extracts the salient surface keypoints with detected scales. Salient geometric features can then be defined collectively on all the detected scale normalized local patches to form a shape descriptor for surface matching purpose. The saliency-driven keypoints are computed as local extrema of the difference of Gaussian function defined over a curved surface in geodesic scale space. This method can properly function on either manifold or non-manifold surface without resorting to any surface mapping or parameterization procedures. Therefore, it has a wide utility in many applications such as shape matching, classification, and recognition. Our experiments on 3D shapes demonstrate that the salient keypoints and local feature descriptors are robust and stable to noisy input and insensitive to resolution change. We have applied our technique to the tasks of 3D shape matching, and the experimental results showed good performance and the effectiveness of this new method. Copyright © 2008 John Wiley & Sons, Ltd.

Grasp synthesis from low-dimensional probabilistic grasp models

Abstract: We propose a novel data-driven animation method for the synthesis of natural looking human grasping. Motion data captured from human grasp actions is used to train a probabilistic model of the human grasp space. This model greatly reduces the high number of degrees of freedom of the human hand to a few dimensions in a continuous grasp space. The low dimensionality of the grasp space in turn allows for efficient optimization when synthesizing grasps for arbitrary objects. The method requires only a short training phase with no need for preprocessing of graphical objects for which grasps are to be synthesized. Copyright © 2008 John Wiley & Sons, Ltd.

A unified handling of immiscible and miscible fluids

Abstract: Conventional level set-based approaches have an inherent difficulty in tracking miscible fluids due to its discrete treatment for interface. This paper proposes a unified framework to efficiently handle both miscible and immiscible fluid simulations. Based on the chemical potential energy, our method describes the evolution of multiple fluids as time-varying concentration fields. Handling of multiple fluids is straightforward and, unlike level set methods, ad hoc reinitialization or fictitious particle deployment is not necessary. For numerical computation of the Navier—Stokes equations, we adopt advanced lattice Boltzmann methods (LBMs) for computational efficiency. The experiments show that our approach works well with immiscible fluids, miscible fluids, and interaction with objects. Copyright © 2008 John Wiley & Sons, Ltd.

2D shape deformation based on rigid square matching

Abstract: In this paper, we propose a fast and stable method for 2D shape deformation based on rigid square matching. Our method utilizes uniform quadrangular control meshes for 2D shapes and tries to maintain the rigidity of each square in the control mesh during user manipulation. A rigid shape matching method is performed to find an optimal pure rotational transformation for each square in the control mesh. An iterative solver is proposed to compute the final deformation result for the entire control mesh by minimizing the difference between the deformed vertices and their counterparts in the neighboring rigid square. The deformation result on the 2D shape is as rigid as possible and the details of the shape are preserved well. As extensions, we present a shape-aware splitting method to improve the deformation effect for coarse meshes and a simple sketch-based clustering method for skeletal deformation. Experiments with various 2D shapes show that our method is efficient and easy to use, and can provide physically plausible result for shapes of objects in real world. Therefore, our shape deformation method is especially suitable for applications in cartoon character animation. Copyright © 2008 John Wiley & Sons, Ltd.

Generation and visualization of emotional states in virtual characters

Abstract: This paper presents an affective model that determines the emotional state of a character according to the personality traits and the experienced emotions. We consider an emotional state as the layer between personality and emotion. The proposed affective model offers a mapping between emotions and emotional states. To evidence emotional states of a virtual character, we can attribute them facial expressions based on their associated emotions. Facial expressions for intermediate emotions are generated automatically from expressions for universal emotions. The experiments show coherent emotional states produced by a simulated story. They also present how the corresponding emotions were represented through dynamic and static facial expressions. Finally, the obtained results demonstrate the satisfactory recognition by a group of people unfamiliar with the work described. Copyright © 2008 John Wiley & Sons, Ltd.

Facial animation by optimized blendshapes from motion capture data

Abstract: This paper presents a labor-saving method to construct optimal facial animation blendshapes from given blendshape sketches and facial motion capture data. At first, a mapping function is established between target “Marker Face” and performer's face by RBF interpolating selected feature points. Sketched blendshapes are transferred to performer's “Marker Face” by using motion vector adjustment technique. Then, the blendshapes of performer's “Marker Face” are optimized according to the facial motion capture data. At last, the optimized blendshapes are inversely transferred to target facial model. Apart from that, this paper also proposes a method of computing blendshape weights from facial motion capture data more accurately. Experiments show that expressive facial animation can be acquired. Copyright © 2008 John Wiley & Sons, Ltd.

Language learning with interactive virtual agent scenarios and speech recognition: Lessons learned

Abstract: The SPELL (Spoken Electronic Language Learning) system is a self-access computer-assisted language learning (CALL) package that integrates speaker-independent continuous speech recognition technology with virtual worlds and embodied virtual agents to create an environment in which learners can converse in the target language within meaningful contextualized scenarios. In this paper we provide an overview of the functionality, architecture, and implementation of the SPELL system. We also describe four phases of usability evaluation conducted with the system and summarize the main results of these user assessments. Finally, we discuss the most significant lessons learned in the development and evaluation of the system. The paper focuses on the technological aspects of the system and its evaluation for usability and robustness, rather than its pedagogical methodology. Copyright © 2008 John Wiley & Sons, Ltd.

Augmented reality agents for user interface adaptation

Abstract: Most augmented reality (AR) applications are primarily concerned with letting a user browse a 3D virtual world registered with the real world. More advanced AR interfaces let the user interact with the mixed environment, but the virtual part is typically rather finite and deterministic. In contrast, autonomous behavior is often desirable in ubiquitous computing (Ubicomp), which requires the computers embedded into the environment to adapt to context and situation without explicit user intervention. We present an AR framework that is enhanced by typical Ubicomp features by dynamically and proactively exploiting previously unknown applications and hardware devices, and adapting the appearance of the user interface to persistently stored and accumulated user preferences. Our framework explores proactive computing, multi-user interface adaptation, and user interface migration. We employ mobile and autonomous agents embodied by real and virtual objects as an interface and interaction metaphor, where agent bodies are able to opportunistically migrate between multiple AR applications and computing platforms to best match the needs of the current application context. We present two pilot applications to illustrate design concepts. Copyright © 2007 John Wiley & Sons, Ltd.

Managing coherent groups

Abstract: The animation of groups of characters involves the generation of some interesting steering behaviors like following a single path, moving toward a common objective, and moving while keeping a formation. This paper presents a new approach to manage the movement of groups in dynamic environments using a simple and robust algorithm that includes a strategy to keep formations during the displacement of the group. Our method is based on a boundary value problem (BVP) involving Laplace's equation and has two layers. In the first one, a group map is built to allow for local control of each individual, while in the second one a path planning is performed for each group as a whole. Results show that our technique is robust to several situations and can be implemented on GPU, which results in real-time performance for large groups. Copyright © 2008 John Wiley & Sons, Ltd.

Shape-constrained flock animation

Abstract: We propose a novel shape-constrained flock animation system for interactively controlling flock navigation in virtual environments. This system is capable of making the spatial distribution of a flock meet static or deforming shape constraints while performing flock simulation. Such a capability can find many applications in the entertainment industry. Given a 3D constraining shape, our system first draws a set of uniform sample points through a 3D surface mosaicing process or a stratified point sampling strategy. Once correspondences between flock members and sample points have been established, points on the target shape are used as homing destinations to guide flock migration. Under a global path control scheme, an effective fuzzy control logic, which dynamically adjusts steering forces and control forces, has been developed to create visually pleasing shape-constrained flock animations. Copyright © 2008 John Wiley & Sons, Ltd.

A physically faithful multigrid method for fast cloth simulation

Abstract: We present an efficient multigrid algorithm that is adequate to solve a heavy linear system given in cloth simulation. Although a multigrid solver has been successfully employed to the Poisson problems, it is hard to apply the solver to complicated cloth deformations due to its lack of physical meaning in level construction. We address this problem by developing a physically faithful technique ensuring the conservation of all physical quantities across levels. The performance of our approach is demonstrated on a number of garment simulations implemented by the state of the art techniques: the implicit integration, the triangle-based in-plane energy model, and the curvature-based bending energy model. Our multigrid algorithm is about four times faster than the preconditioned Conjugate Gradient method for a garment with 20K particles. Copyright © 2008 John Wiley & Sons, Ltd.

3D virtual simulator for breast plastic surgery

Abstract: We have proposed novel 3D virtual simulation software for breast plastic surgery. Our software comprises two processes: a 3D torso modeling and a virtual simulation of the surgery result. First, image-based modeling is performed in order to obtain a female subject's 3D torso data. Our image-based modeling method utilizes a template model, and this is deformed according to the patient's photographs. For the deformation, we applied procrustes analysis and radial basis functions (RBF). In order to enhance reality, the subject's photographs are mapped onto a mesh. Second, from the modeled subject data, we simulate the subject's virtual appearance after the plastic surgery by morphing the shape of the breasts. We solve the simulation problem by an example-based approach. The subject's virtual shape is obtained from the relations between the pair sets of feature points from previous patients' photographs obtained before and after the surgery. Copyright © 2008 John Wiley & Sons, Ltd.

An efficient dynamic point algorithm for line-based collision detection in real time virtual environments involving haptics

Abstract: In real time computer graphics, “interactivity” is limited to a display rate of 30 frames per second. However, in multimodal virtual environments involving haptic interactions, a much higher update rate of about 1 kHz is necessary to ensure continuous interactions and smooth transitions. The simplest and most efficient interaction paradigm in such environments is to represent the haptic cursor as a point. However, in many situations, such as those in the development of real time medical simulations involving the interactions of long slender surgical tools with soft deformable organs, such a paradigm is nonrealistic and at least a line-based interaction is desirable. While such paradigms exist, the main impediment to their widespread use is the associated computational complexity. In this paper, we introduce, for the first time, an efficient algorithm for computing the interaction of a line-shaped haptic cursor and polygonal surface models which has a near constant complexity. The algorithm relies on space-time coherence, topological information, and the properties of lines in 3D space to maintain proximity information between a line segment and triangle meshes. For interaction with convex objects, the line is represented by its end points and a dynamic point, which is the closest point on the line to any potentially colliding triangle. To deal with multiple contacts and non-convexities, the line is decomposed into segments and a dynamic point is used for each segment. The algorithm may be used to compute collision detection and response with rigid as well as deformable objects with no performance penalty. Realistic examples are presented to demonstrate the effectiveness of our approach. Copyright © 2008 John Wiley & Sons, Ltd.

Adding variation to path planning

Abstract: Path planning in computer games, whether these are serious or entertainment games, plays an important role in the immersion of a player. Recently, the concept of path planning inside corridors has been introduced and a novel approach under the name Corridor Map Method (CMM) has been proposed. In this paper, we extend the original CMM by creating alternative paths that a character can follow within a corridor. This not only presents a more challenging and less predictable opponent for the player, but also enhances the realism of the gaming and-or training experience. We also discuss how variation in the speed of the animated characters can be integrated into our extended framework, leading to convincing characters that exhibit human like path planning. Copyright © 2008 John Wiley & Sons, Ltd.

Motion adaptation based on character shape

Abstract: With the increasing performances of the graphics hardware, virtual reality applications are reaching a new level of realism. It is now possible to animate entire crowds of virtual avatars, or to display in real-time highly realistic deformable characters. This new type of applications requires that characters are deformed, either to generate a large number of individuals for creating a crowd, or to match a particular shape. To make the animation fit to the animated character and to prevent self-collisions, adapting the motion is mandatory. Unlike previous approaches which relied on skeletal models, this paper presents a method considering the actual shape of the character's body to perform the adaptation. Our approach uses spacetime optimization to remove the self-penetration, and finally re-establishes the balance of the motion. We also introduce an interpolation scheme based on radial basis functions that can blend pre-calculated adaptations, and thus achieve real-time performances. Copyright © 2008 John Wiley & Sons, Ltd.

Shear buckling and dynamic bending in cloth simulation

Abstract: This paper addresses the problem of simulating the mechanical behavior of cloth in computer animation, which is very important and challenging. The micro-structure of woven fabrics leads to significantly different shear reaction from other sheet materials, which has been neglected in previous approaches of cloth simulation. Therefore, it is beneficial for cloth simulation to model the shear buckling and structural bending separately. We analyze the shear buckling yielded by the micro-structure of woven and the dynamic bending based on the thin-shell theory, and develop a compact implementation of the new model on mass-spring systems. Experimental results show that the animations generated using this technique are with wrinkles and folds appearing and vanishing in a more natural way than other approaches. Copyright © 2008 John Wiley & Sons, Ltd.

Dynamic skin deformation with characteristic curves

Abstract: By simulating motion and deformation of a set of 3D characteristic curves defining surfaces, we introduce a new skin deformation technique to animate skin deformation of character models. This technique consists of two parts, representation of characteristic curves and dynamic skin deformation. The first part is to extract characteristic curves of an existing model, that is a polygon model or a NURBS model, represent the characteristic curves with time-dependent 3D trigonometric curves, and relate the surface points of the model to these trigonometric curves. The advantage of such a treatment is that it can transform an original 3D problem into a 2D problem, making it much quicker and easier to process and compute. In the second part, a vector-valued dynamic fourth-order differential equation is employed to govern the behaviour of the time-dependent 3D trigonometric curves. These dynamic differential equations incorporate both the time component and the physical properties of the material, which are given by the user. Thus, the character model can be made to animate (deform) following the user-specified behaviour parameters. Our experiments demonstrate that this technique is able to produce realistic skin deformations efficiently and avoid the undesirable skinning problems suffered by some existing skinning techniques. Copyright © 2008 John Wiley & Sons, Ltd.

Dynamically populating large urban environments with ambient virtual humans

Abstract: Creating an interactive simulation of a large urban environment populated with virtual humans poses a number of interesting challenges, ranging from how to initialise the virtual humans in the correct locations to maintaining a real-time simulation. When considering a large environment it is beneficial to investigate automatic techniques that create and simulate virtual humans using the available computing resources effectively. In this paper, two contributions towards the population of a large environment are described. The first presents two methods that use an automatic analysis of the urban environment to determine the required population densities throughout the scene. These methods ensure that the virtual humans are distributed such that main high streets consistently exhibit a higher number of virtual humans than other areas. The methods presented here achieve above 90% correlation to the predicted population densities for the environment, which outperforms the state of the art. The second contribution concerns the optimisation of the two methods to facilitate their applicability to large environments. The methods presented are modified to insert virtual humans dynamically into the behaviour system when required. The approach limits the required computing resources whilst achieving above 75% correlation to the predicted population values. Copyright © 2008 John Wiley & Sons, Ltd.

Perspective-aware cartoon clips synthesis

Abstract: In this paper we propose an approach, which allows the users to synthesize cartoon clips according to the perspective of the background image. In order to construct the cartoons smoothly, the character's edge distance and motion direction distance are demonstrated to be the factors affecting the human perception in similarity evaluation, and utilized in cartoon clips synthesis. When applying the generated cartoons to the background image, in which the perspective exists, the size of the character is coordinated according to the scaling factor calculated from the vanishing line. The experiment results demonstrate that our approach can synthesize the cartoon clips more smoothly compared with other single frame reusing strategies. The generated cartoons, which are applied to the background image, can be accepted by the human perception well. Copyright © 2008 John Wiley & Sons, Ltd.

A social agent pedestrian model

Abstract: This paper presents a social agent pedestrian model based on experiments with human subjects. Research studies of criminology and environmental psychology show that certain features of the urban environment generate fear in people, causing them to take alternate routes. The Crime Prevention Through Environmental Design (CPTED) strategy has been implemented to reduce fear of crime and crime itself. Our initial prototype of a pedestrian model was developed based on these findings of criminology research. In the course of validating our model, we constructed a virtual environment (VE) that resembles a well-known fear-generating area where several decision points were set up. 60 human subjects were invited to navigate the VE and their choices of routes and comments during the post interviews were analyzed using statistical techniques and content analysis. Through our experimental results, we gained new insights into pedestrians' behavior and suggest a new enhanced and articulated agent model of a pedestrian. Our research not only provides a realistic pedestrian model, but also a new methodology for criminology research. Copyright © 2008 John Wiley & Sons, Ltd.

Style subspaces for character animation

Abstract: In this paper, we present a novel method for editing stylistic human motions. We represent styles as differences between stylistic and introduced neutral motions, including timing differences and spatial differences. Timing differences are defined as time alignment curves, while spatial differences are found by a machine learning technique: independent feature subspaces analysis, which is the combination of multidimensional independent component analysis and invariant feature subspaces. This technique is used to decompose two motions into several subspaces. One of these subspaces can be defined as style subspace that describes the style aspects of the stylistic motion. In order to find the style subspace, we compare norms of the projections of two motions on each subspace. Once the time alignment curves and style subspaces of several motion clips are obtained, animators can tune, transfer, and merge the style subspaces to synthesize new motion clips with various styles. Our method is easy to use since manual manipulations and large training data sets are not necessary. Copyright © 2008 John Wiley & Sons, Ltd.

A survey of mobile and wireless technologies for augmented reality systems

Abstract: Recent advances in hardware and software for mobile computing have enabled a new breed of mobile augmented reality (AR) systems and applications. A new breed of computing called augmented ubiquitou...

A comparative study of awareness methods for peer-to-peer distributed virtual environments

Abstract: The increasing popularity of multi-player online games is leading to the widespread use of large-scale Distributed Virtual Environments (DVEs) nowadays In these systems, peer-to-peer (P2P) architectures have been proposed as an efficient and scalable solution for supporting massively multi-player applications However, the main challenge for P2P architectures consists of providing each avatar with updated information about which other avatars are its neighbors This problem is known as the awareness problem In this paper, we propose a comparative study of the performance provided by those awareness methods that are supposed to fully solve the awareness problem This study is performed using well-known performance metrics in distributed systems Moreover, while the evaluations shown in the literature are performed by executing P2P simulations on a single (sequential) computer, this paper evaluates the performance of the considered methods on actually distributed systems The evaluation results show that only a single method actually provides full awareness to avatars This method also provides the best performance results Copyright © 2008 John Wiley & Sons, Ltd

The embodied Web: embodied Web-services interaction with an umbrella for augmented city experiences

Abstract: This paper introduces the embodied Web, a new design paradigm for mobile devices. The embodied Web aims to provide an interface using real-world embodied interaction to provide a computer-augmented reality that accesses web services. This platform regards embodied interaction at three levels: operational level, activity level and social level; and is implemented with a combination of sensor, actuator and network connectivities. The platform is developed as a complex of hardware, software and network services. The implementation takes an approach of modularization of hardware, software and web services. As a practical prototype of the embodied Web, the Internet Umbrella Pileus was developed and tested. In contrast to the small screens of mobile devices, Pileus has a big screen on the underside of the umbrella, and it is operated by embodied interaction, including motion sensing of the device and location sensing of walking activities. Photo-sharing and 3D map navigation is provided on the umbrella to expand the user's activity area. These services are provided by API hookups with Flickr and Google Earth. Pileus has been iteratively developed from user observations, design observations and intuitions and prototype evaluations. The umbrella was tested in a large urban environment (the city of Tokyo). Copyright © 2008 John Wiley & Sons, Ltd.

A scalable interest management scheme for distributed virtual environments

Abstract: With the expansion of the internet and its bandwidth, distributed virtual environment (DVE) applications have become more prevalent. In DVE applications, users frequently crowd in a specific place, and a key aspect to consider is how to provide interactive performance for users. However, existing approaches using multicast require users to receive uninteresting messages. Even though recent works have addressed fine-grained filtering, they still incur other drawbacks in terms of assigning lots of multicast addresses or handling overhead of multicast groups. This makes the system less scalable as the number of users increases. In this paper, we propose a new scalable filtering scheme that reduces not only the number of messages during interaction in a region and among neighboring regions, but also the number of multicast addresses without significant computational overhead. Interest management in a region dynamically creates groups of users with the same interests. While members communicate with each other with high fidelity, a representative sends information to non-members with low frequency. For interaction among neighboring regions, we propose a sub-region concept to select only a subset of users from the neighboring regions based on proximity, the distribution of the users' locations, and the viewing direction of a user. Copyright © 2007 John Wiley & Sons, Ltd.