We study the detection of misbehavior in a Gaussian relay system, where the source transmits information to the destination with the assistance of an amplify-and-forward relay node subject to unreliable channel state information (CSI). The relay node may be potentially malicious and corrupt the network by forwarding garbled information. In this situation, misleading feedback may take place, since reliable CSI is unavailable at the source and/or the destination. By classifying the action of the relay as detectable or undetectable, we propose a novel approach that is capable of coping with any malicious attack detected and continuing to work effectively in the presence of unreliable CSI. We demonstrate that the detectable class of attacks can be successfully detected with a high probability. Meanwhile, the undetectable class of attacks does not affect the performance improvements that are achievable by cooperative diversity, even though such an attack may fool the proposed detection approach. We also extend the method to deal with the case in which there is no direct link between the source and the destination. The effectiveness of the proposed approach has been validated by numerical results.

Effective management and visualization of scientific and research documents can greatly assist researchers by improving understanding of relationships (e.g. citations) between the documents. This paper presents work on the management and visualization of large corpuses of scientific papers in order to help researchers explore their citation relationships. Term selection and weighting are used for mining citation relationships by identifying the most relevant. To this end, we present a variation of the TF-IDF scheme, which uses external domain resources as references to calculate the term weighting in a particular domain; document weighting is taken into account in the calculation of term weighting from a group of citations. A simple hierarchical word weighting method is also presented. The work is supported by an underlying architecture for document management using NoSQL databases and employs a simple visualization interface.

Abstract Interactive isosurface visualisation has been made possible by mapping algorithms to GPU architectures. However, current state‐of‐the‐art isosurfacing algorithms usually consume large amounts of GPU memory owing to the additional acceleration structures they require. As a result, the continued limitations on available GPU memory mean that they are unable to deal with the larger datasets that are now increasingly becoming prevalent. This paper proposes a new parallel isosurface‐extraction algorithm that exploits the blocked organisation of the parallel threads found in modern many‐core platforms to achieve fast isosurface extraction and reduce the associated memory requirements. This is achieved by optimising thread co‐operation within thread‐blocks and reducing redundant computation; ultimately, an indexed triangular mesh can be produced. Experiments have shown that the proposed algorithm is much faster (up to 10×) than state‐of‐the‐art GPU algorithms and has a much smaller memory footprint, enabling it to handle much larger datasets (up to 64×) on the same GPU.

RT3S is an EU-funded project in an area of e-health - ICT for Patient Safety. Specifically, RT3S is developing a patient-centred, probabilistic model for peripheral stent fatigue-fracture, integrated within a real-time, computer-aided surgery planning application. RT3S will provide advice on fracture risk for individual combinations of patient anatomy and stent design. Alongside the pre-operational software tool, which is addressed mainly to interventional radiologists, RT3S has also developed a training application that will be of benefit to trainee vascular interventionists and engineers in medical device companies. This paper provides an overview of the work performed during nearly three years of project activities and also addresses the motivation leading to RT3S and the expected impact.

MyHealthAvatar is designed to provide a digital representation of patient health status. It aims to become a `lifetime companion' for individual citizens that will facilitate the collection of, and access to, long term health-status information. This avatar is not only extremely valuable for clinical decision-making, but it will generate data to support clinical investigation, thereby leading to strengthened multidisciplinary research and excellence in supporting innovative medical care across the population. My Health Avatar platform is currently under development. The purpose of this paper is to present the scope, the provided service and the future plans of the platform as well as a detailed description of the visual representation of the MyHealthAvatar platform.

Vascular stent deployment in peripheral arteries is a medical intervention in which a wire mesh tube is inserted into the artery to provide internal support. However, stents positioned in locations such as the femoral artery are subject to cyclic bending, and are therefore at risk of fatigue fracture. A software tool chain, called AimaSimul, is being implemented to support stent modeling, surgical simulation and risk calculation for surgical planning. In particular, the AimaSimul preoperative planning tool allows clinicians, starting from patient-specific medical images, to interactively assess different stent models and deployment options for the risk of breakage. This paper describes the main functionalities of AimaSimul and, in particular, the stent deployment and deformation.

In this paper, we introduce a diagnosis and treatment for amblyopia performed through a game suitable for children aged between 3 and 7. Our method places emphasis on cooperation between the two eyes to achieve a good binocular outcome to aid the recovery of depth perception. Our approach is not limited to a particular device or platform nor even to a aprticular form of game. Several prototype games have been developed, including 2D games and 3D games.

The visualisation of whole-body anatomy has a variety of applications in health-related analysis and simulation. However, the rendering of complex 3D human anatomy models is generally performed by standalone applications rather than via a web interface, as rendering large 3D models has always been a weak spot of traditional web browsers. Consequently, online access to, and exploration of, the human anatomy in 3D has not been feasible in the past. With the advent of WebGL and HTML5, high performance OpenGL rendering seamlessly integrated with the web interface is now within reach, and this opens the possibility of visualising avatar-centered health data via a web interface. In this paper, a WebGL-based prototype for rendering whole-body anatomy is introduced, and the technical details are presented.

This paper presents the proof-of-concept design of the data repository for 4D digital avatars in the MyHealthAvatar project. Taking account of the privacy and legal issues of patient health information, the research generates a set of synthetic data based on publicly available survey data. At the prototype stage, these synthetic data are used in the scenarios of data storage and management. The paper discusses the early proof-of-concept design of the technical stack which enables the storage and query of large scale patients' health data and empowers the future data mining and analysis for health care support. It provides the first stage implementation and the use of it for data analytics.

Volume up scaling enlarges the size of a volume to make feature analysis more accurate and efficient. Linear interpolation, widely used in volume up scaling, result in jagged artifacts around features and losses of high-frequency components. Based on the example-based up scaling framework, this paper presents a new high-quality volume up scaling technique, predicting the high-frequency components by searching for the best matched patch in the input volume. As each slice can be taken as an image, the existing image up scaling technique based on the local self-similarity assumption can be directly applied to achieve slice up scaling. We further validate that the local self-similarity assumption is still valid for 3D volumes, and we extend this technique to 3D volume up scaling, i.e., isotropic volume up scaling. We compare our volume up scaling technique with traditional linear and cubic spline interpolations, and demonstrate that our method can generate a higher quality volume with better shape and details preserved. The proposed volume up scaling technique is well suitable for legacy low-resolution volumes to improve their visual qualities in visualization and analysis.

In many biomedical applications, it is often desired to simulate, analyse and visualise the dynamics of a particular patient based on a patient-specific musculoskeletal model. However, reconstructing a patient-specific model directly from medical images is highly labour intensive, and impractical in the clinical context. A more efficient method is to derive it from an atlas musculoskeletal model using patient-specific hints. In this paper, Laplacian mesh processing is introduced to deform an atlas model to a patient-specific model, based on patient-specific landmarks extracted from two orthogonal clinical images and using least-squares error optimization. Muscle attachment landmarks and motion landmarks in the atlas are also transformed as part of the process. Drift and inter-surface penetrations are prevented by supplementary inter-surface landmarks. Mesh simplification and reconstruction are used to avoid out-of-memory failures that may result from trying to deform models at high resolution.

Abstract The aim of removing camera shake is to estimate a sharp version x from a shaken image y when the blur kernel k is unknown. Recent research on this topic evolved through two paradigms called and . only solves for k by marginalizing the image prior, while recovers both x and k by selecting the mode of the posterior distribution. This paper first systematically analyses the latent limitations of these two estimators through Bayesian analysis. We explain the reason why it is so difficult for image statistics to solve the previously reported failure. Then we show that the leading methods, which depend on efficient prediction of large step edges, are not robust to natural images due to the diversity of edges. , although much more robust to diverse edges, is constrained by two factors: the prior variation over different images, and the ratio between image size and kernel size. To overcome these limitations, we introduce an inter‐scale prior prediction scheme and a principled mechanism for integrating the sharpening filter into . Both qualitative results and extensive quantitative comparisons demonstrate that our algorithm outperforms state‐of‐the‐art methods.

Blind motion deblurring estimates a sharp image from a motion blurred image without the knowledge of the blur kernel. Although significant progress has been made on tackling this problem, existing methods, when applied to highly diverse natural images, are still far from stable. This paper focuses on the robustness of blind motion deblurring methods toward image diversity-a critical problem that has been previously neglected for years. We classify the existing methods into two schemes and analyze their robustness using an image set consisting of 1.2 million natural images. The first scheme is edge-specific, as it relies on the detection and prediction of large-scale step edges. This scheme is sensitive to the diversity of the image edges in natural images. The second scheme is nonedge-specific and explores various image statistics, such as the prior distributions. This scheme is sensitive to statistical variation over different images. Based on the analysis, we address the robustness by proposing a novel nonedge-specific adaptive scheme (NEAS), which features a new prior that is adaptive to the variety of textures in natural images. By comparing the performance of NEAS against the existing methods on a very large image set, we demonstrate its advance beyond the state-of-the-art.

We present a novel approach for GPU-based high-quality volume rendering of large out-of-core volume data. By focusing on the locations and costs of ray traversal, we are able to significantly reduce the rendering time over traditional algorithms. We store a volume in an octree (of bricks); in addition, every brick is further split into regular macrocells. Our solutions move the branch-intensive accelerating structure traversal out of the GPU raycasting loop and introduce an efficient empty-space culling method by rasterizing the proxy geometry of a view-dependent cut of the octree nodes. This rasterization pass can capture all of the bricks that the ray penetrates in a per-pixel list. Since the per-pixel list is captured in a front-to-back order, our raycasting pass needs only to cast rays inside the tighter ray segments. As a result, we achieve two levels of empty space skipping: the brick level and the macrocell level. During evaluation and testing, this technique achieved 2 to 4 times faster rendering speed than a current state-of-the-art algorithm across a variety of data sets.

The MSV project aims to survey current best practice in multiscale visualisation and to construct a software toolkit which will make multiscale techniques readily accessible to biomedical researchers and clinicians. In this paper, current methods for multiscale data visualisation in several domains are reviewed, and a novel classification of multiscale techniques for biomedical applications by function is proposed. The classification will form the basis of a design menu and toolkit for multiscale visualisation.

Lighting design is a complex, but fundamental, problem in many fields. In volume visualization, direct volume rendering generates an informative image without external lighting, as each voxel itself emits radiance. However, external lighting further improves the shape and detail perception of features, and it also determines the effectiveness of the communication of feature information. The human visual system is highly effective in extracting structural information from images, and to assist it further, this paper presents an approach to structure-aware automatic lighting design by measuring the structural changes between the images with and without external lighting. Given a transfer function and a viewpoint, the optimal lighting parameters are those that provide the greatest enhancement to structural information - the shape and detail information of features are conveyed most clearly by the optimal lighting parameters. Besides lighting goodness, the proposed metric can also be used to evaluate lighting similarity and stability between two sets of lighting parameters. Lighting similarity can be used to optimize the selection of multiple light sources so that different light sources can reveal distinct structural information. Our experiments with several volume data sets demonstrate the effectiveness of the structure-aware lighting design approach. It is well suited to use by novices as it requires little technical understanding of the rendering parameters associated with direct volume rendering.

Halos are usually used to enhance depth perception and display spatial relationships in illustrative visualization. In this paper, we present a simple and effective method to create volumetric halo illustration. In the pre-processing stage, we generate a view-independent halo intensity volume, which contains all potential halos around the boundaries of features, based on the opacity volume on graphic hardware. During halo rendering, the halo intensity volume is used to extract halos only around the contours of structures for the current viewpoint. The performance of our approach is significantly faster than previous halo illustration methods, which perform both halo generation and rendering during volume rendering. Experimental results demonstrate volumetric halo effects and the efficiency of the proposed approach.

Simulators of tumour growth can estimate the evolution of tumour volume and the quantity of various categories of cells as functions of time. However, the execution time of each simulation often takes several dozens of minutes (depending upon the dataset resolution), which clearly prevents easy interaction. The modern graphics processing unit (GPU) is not only a powerful graphics engine but also a highly parallel programmable processor featuring peak arithmetic performance and memory bandwidth that substantially outpaces its CPU counterpart. However, despite this, the GPU is little used in the context of the Virtual Physiological Human (VPH). This paper provides a case study to demonstrate the performance advantages that can be gained by using the GPU appropriately in the context of a VPH project in which the study of tumour growth is a central activity. We also analyse the algorithm performance on different modern parallel processing architectures, including multicore CPU and many-core GPU.

This paper proposes an easy way to perform web-based 3D interactive visualisation, which accepts two data resources, local and remote, as input and copes with two types of algorithm, built-in and remote. The focus of this paper is the biomedical area. Today's web technology makes it possible to use software maintained on a remote server. The approach described provides a virtual client environment, in which users can employ remotely installed software interactively using any standard browser. The proposed approach is a generic one and can be used in many other application areas.

Medical visualisation is an indispensable means for doctors and researchers to better explore and analyse medical images. The EC-funded ContraCancrum project, which aims at more predictable tumour simulation and treatment, uses visualisation as an important tool to interactively display tumour development and tumour simulation. This paper presents CCVis - the visualisation tool in ContraCancrum - which is a Qt-based plug in of the DrEye platform. CCVis uses a unified architecture for visualisation of the patient image data and tumour simulation data. It provides axis-aligned and arbitrary slice views, is surface rendering and volume ray casting as well as time-varying visualisation of patient image series and simulation data. Statistics in tumour simulation are plotted as 2D graphs. Major extensions of the Visualization Toolkit (VTK) are made to meet the demands for label highlighting and multi-dimensional transfer function.

While there has been significant progress in the treatment of ischemic heart failure, it remains a significant health and economic problem worldwide. In this paper, we present the challenges of modelling ischemic heart failure and introduce a user-friendly software system that will be a sub-set of the Virtual Pathological Heart environment which is currently being developed under the FP7 VPH2 project. This will provide patient-specific computational modelling and simulation of the human heart to assist the cardiologist and the cardiac surgeon in defining the severity and extent of disease in patients with post-ischemic Left Ventricular Dysfunction. The proposed system will provide visualisation tools for surgical assessment and planning: the registration and display of necrotic and hypo-kinetic regions; simulated surgical restoration (cutting and patching); and finally post-operative functional prediction (volume, shape and mitral valve regurgitation).

Web services provide remote access to distributed resources and processes through uniform interfaces. However, the latency associated with data transmission has meant that they are generally applied to non-interactive data processing. Interactive applications, in which many more user interactions and data transmissions are involved, are difficult to adapt to web service based frameworks, particularly if the interactive investigation involves large datasets. In medical imaging and visualisation, user interactions are generally a prerequisite for the detailed study and manipulation of data. As a result of major scientific initiatives, such as the Virtual Physiological Human, in which large data repositories are being set up at a variety of sites, it is becoming increasingly common for the data being investigated to be stored on a remote server. Consequently, it is now highly desirable to develop a means by which web service based interactive visualisation can be applied to distributed medical data access and clinical collaboration. This paper presents a functional-level plug-in based architecture for interactive data visualisation via web services which is being implemented within the EC-funded ContraCancrum project.

Clustering algorithms have been popularly applied in tissue segmentation in MRI. However, traditional clustering algorithms could not take advantage of some prior knowledge of data even when it does exist. In this paper, we propose a new approach to tissue segmentation of 3D brain MRI using semi-supervised spectral clustering. Spectral clustering algorithm is more powerful than traditional clustering algorithms since it models the voxel-to-voxel relationship as opposed to voxel-to-cluster relationships. In the semi-supervised spectral clustering, two types of instance-level constraints: must-link and cannot-link as background prior knowledge are incorporated into spectral clustering, and the self-tuning parameter is applied to avoid the selection of the scaling parameter of spectral clustering. The semi-supervised spectral clustering is an effective tissue segmentation method because of its advantages in (1) better discovery of real data structure since there is no cluster shape restriction, (2) high quality segmentation results as it can obtain the global optimal solutions in the relaxed continuous domain by eigen-decomposition and combines the pairwise constraints information. Experimental results on simulated and real MRI data demonstrate its effectiveness.

Abstract Empty‐space skipping is an essential acceleration technique for volume rendering. Image‐order empty‐space skipping is not well suited to GPU implementation, since it must perform checks on, essentially, a per‐sample basis, as in kd‐tree traversal, which can lead to a great deal of divergent branching at runtime, which is very expensive in a modern GPU pipeline. In contrast, object‐order empty‐space skipping is extremely fast on a GPU and has negligible overheads compared with approaches without empty‐space skipping, since it employs the hardware unit for rasterisation. However, previous object‐order algorithms have been able to skip only exterior empty space and not the interior empty space that lies inside or between volume objects. In this paper, we address these issues by proposing a multi‐layer depth‐peeling approach that can obtain all of the depth layers of the tight‐fitting bounding geometry of the isosurface by a single rasterising pass. The maximum count of layers peeled by our approach can be up to thousands, while maintaining 32‐bit float‐point accuracy, which was not possible previously. By raytracing only the valid ray segments between each consecutive pair of depth layers, we can skip both the interior and exterior empty space efficiently. In comparisons with 3 state‐of‐the‐art GPU isosurface rendering algorithms, this technique achieved much faster rendering across a variety of data sets.

Viewpoint selection is becoming a useful part in the volume visualization pipeline, as it further improves the efficiency of data understanding by providing representative viewpoints. We present two structure-aware view descriptors, which are the shape view descriptor and the detail view descriptor, to select the optimal viewpoint with the maximum amount of the structural information. These two proposed structure-aware view descriptors are both based on the gradient direction, as the gradient is a well-defined measurement of boundary structures, which have been proved as features of interest in many applications. The shape view descriptor is designed to evaluate the overall orientation of features of interest. For estimating local details, we employ the bilateral filter to construct the shape volume. The bilateral filter is very effective in smoothing local details and preserving strong boundary structures at the same time. Therefore, large-scale global structures are in the shape volume, while small-scale local details still remain in the original volume. The detail view descriptor measures the amount of visible details on boundary structures in terms of variances in the local structure between the shape volume and the original volume. These two view descriptors can be integrated into a viewpoint selection framework, and this framework can emphasize global structures or local details with flexibility tailored to the user's specific situations. We performed experiments on various types of volume datasets. These experiments verify the effectiveness of our proposed view descriptors, and the proposed viewpoint selection framework actually locates the optimal viewpoints that show the maximum amount of the structural information.

Abstract In this paper, we propose an efficient solution that addresses the performance problems of current single‐pass GPU raycasting algorithms. Our paper provides more control over the rendering process by introducing tighter ray segments for raycasting, while at the same time avoiding the introduction of any new rendering artefacts. We achieve this by dynamically generating, on the GPU, a coarsely fitted proxy geometry, composed of spheres, for the active blocks. The spheres are then rasterised into two z‐buffers by a single rendering pass. The resulting two z‐buffers are used as the first‐hit and last‐hit points for the subsequent raycaster. With this approach, only the valid ray segments between the two z‐buffers need to be sampled during raycasting. This also provides more coherent parallelism on the GPU due to more consistent ray length and avoidance of the overheads and dynamic branching of performing checks on a per‐sample basis during the raycasting pass. Our technique is ideal for dynamic data exploration in which both the transfer function and view parameters need to be changed frequently at runtime. The rendering results of our algorithm are identical to the general cube‐based proxy geometry algorithm, but the performance can be up to 15.7 times faster. Furthermore, the approach can be adopted by any existing raycasting system in a straightforward way.

Abstract This paper presents a fast, high‐quality, GPU‐based isosurface rendering pipeline for implicit surfaces defined by a regular volumetric grid. GPUs are designed primarily for use with polygonal primitives, rather than volume primitives, but here we directly treat each volume cell as a single rendering primitive by designing a vertex program and fragment program on a commodity GPU. Compared with previous raycasting methods, ours has a more effective memory footprint (cache locality) and better coherence between multiple parallel SIMD processors. Furthermore, we extend and speed up our approach by introducing a new view‐dependent sorting algorithm to take advantage of the early‐z‐culling feature of the GPU to gain significant performance speed‐up. As another advantage, this sorting algorithm makes multiple transparent isosurfaces rendering available almost for free. Finally, we demonstrate the effectiveness and quality of our techniques in several real‐time rendering scenarios and include analysis and comparisons with previous work.

In bioinformatics experiments related to in silico modelling, huge sets of data at different physical scales, and frequently from different scientific laboratories, are created. Likewise, the data processing algorithms being used have been developed by researchers in different institutions; some are newly created, some have been in use for a long time. It remains a huge challenge to share and manage these data and algorithms on the Internet. It can be valuable to build a digital library infrastructure which allows clinicians and researchers not only to preserve, trace and share data resources, but also to collaborate at the data processing level. This paper presents a Web Services approach within the LHDL project, which allows medical data in differing formats to be made compatible by being stored in a standard form and also exposes key algorithms from existing applications as online service objects for sharing and validating.

The aim of this review paper is to report on the current state of the art in creating in silico humans able to simulate the biomechanics of the human body at all scales of interest. The focus is on the musculoskeletal apparatus, although much of what is written is valid also for the biomechanical modeling of other organs. The state of the art of computational biomechanics at body, organ, tissue, and cell levels is briefly described and the most recent achievements in the area of multiscale models are discussed. In conclusion, the challenges to be faced to realize a true living human model are summarized. It is evident that the demands associated with some of these challenges greatly exceed the potential currently possessed by the computational biomechanics research community. Thus, to tackle them it will be necessary not only to coordinate all efforts in a coherent way,but also to mobilize much greater financial and human resources than are currently available.

Abstract This paper proposes a patch‐based texture synthesis approach that cuts and stitches irregularly shaped texture patches to generate new texture images with minimized visual discontinuity. It works well on a wide range of textures. A semiautomatic algorithm is developed to obtain the irregularly shaped patches. To synthesize strictly structured textures, a regular pasting method is proposed to identify the texture structures and subsequently position the irregularly shaped patches according to the identified structures. The results and comparisons with related work are given.

The DataManager presented in this paper allows the multimodal visualisation of heterogeneous data originating from the biomedical field and, more particularly, biomechanics. In the latter, the aim is to increase our understanding of the musculo-skeletal system, and to achieve this, numerous disparate data must be collected and combined. Previously, no software tool fully allowed such integration, but the DataManager and its development environment (the MAF) now provide an answer to that problem. This paper presents the current visualisation and data processing tools available from the DataManager. Its usefulness for research, educational and clinical activities will be demonstrated. The system developers hope that the data management mechanisms available within the software will stimulate data sharing between scientists and will encourage them to participate in enhancing the system by integrating their own software tools.

This work gives an overview of real-time visualisation algorithms developed under the EC-funded project Multimod to support a novel paradigm for the virtual representation of musculo-skeletal structures. These algorithms are fully integrated into the Multimod Application Framework (MAF), an open-source freely-available software framework for the rapid development of medical visualisation applications. MAF is based on the visualisation toolkit (VTK) and other specialised toolkits, e.g. for image registration and segmentation, collision detection or numerical computation. MAF provides a range of high-level components that can be easily combined for rapid construction of visualisation applications that support synchronised views. The majority of algorithms available within the standard underlying MAF toolkits were frequently either too slow or too general for our purposes. We have thus implemented computationally efficient versions of existing algorithms, e.g. for surface and volume rendering, and more importantly, developed new techniques, e.g. for X-ray rendering and designing volume rendering transfer functions. To achieve interactive rendering we have employed a scheme for space partitioning. The emphasis is on exploiting the characteristics of medical datasets (e.g. density value homogeneity) but further utilising the hardware-accelerated capabilities of modern graphics cards. In this context, calculations are moved into hardware as appropriate while avoiding dependency on specialised features of particular manufacturers so as to ensure real code portability.

We give a brief overview of a new source of data on human anatomy and kinematics created by the EC-funded project VAKHUM. The motivation was to provide support for education at various levels through animated 3D models and finite element meshes of human joints, while making original high-quality raw data available for industrial users. We outline some identified user demands. We further describe the data types and relevant software components employed for accessing and visualising VAKHUM models. The emphasis is on a novel user interface based on focal points and intuitive 3D controls for viewing anatomy that is appropriately registered with kinematics captured by local e.g. electrogoniometry or global e.g. stereophotogrammetry means. The operating scenario for accessing models in the VAKHUM database is outlined. We close with a summary of the work and pointers to future development.

A method of increasing the realism of nonverbal interaction in 3D is proposed. The method is aimed at creating truly believable autonomous actors in virtual environments. A simple action-reaction interaction model with a predefined set of actions is used. The actions are recognised using weighted-directed graphs (Markov models), using a set of control points as features to reduce the dimensionality of the recognition task, thus enabling fast and effective recognition. The method naturally implements characteristics such as reaction delay and gradual recognition with possible mistakes. The approach is tested on a simplified boxing scenario.

In the context of using virtual environments (VEs) in Internet-based teleoperation, this paper addresses the issue of parameter acquisition for single-image-based modeling of VEs. By studying the properties of basic three-dimensional features such as point sets and edge corners, a parameter-searching method was developed that employs virtual objects as feature-matching templates. This approach is particularly valuable if the environment is subject to unpredictable change.

For pt.I. see ibid., p.383-8. This paper addresses the issue of path planning in a virtual environment (VE) for the control of an Internet-based robot manipulator. A hybrid method is proposed in which the dimension of the path-planning problem is reduced by separating the problem of planning the position of the gripper from that of planning the pose of the gripper. A global configuration-space technique is used for the former and a local operational-space technique is used for the latter. Particular attention is paid to fundamental issues such as mapping the graphical model into configuration space, on-line collision detection and obstacle avoidance in the VE.

This paper proposes a new approach for motion retargeting, i.e., adjusting motion-capture data to different characters and scenes. For achieving universality, the existing retargeting techniques often become absolutely impractical for most of real-life applications. In contrast, we did not try to create a technique that can deal with practically any motion, but concentrated on creating a practical solution that is able to produce realistic results for a some subset of all motions. So, the corner-stone idea of our approach is that realistic retargeting can only be achieved if the algorithm is aware about the structure and specific features of the processed motion. We applied this idea to animation of human locomotion and developed a motion-analysis algorithm that can identify type/structure of the motion and extract a lot of useful information, such as gait phases, foot-ground constraints, important features that should be preserved during retargeting, etc. Also, we developed an inverse kinematics-based retargeting solver that can take advantage of using this information and can produce accurate and realistic animations of human locomotion.

Muscle simulation is an important component of human modeling, but there have been few attempts to demonstrate, in 3D and in an anatomically correct way, the structures of muscles and the way in which these change during motion. This paper proposes an anatomically-based approach to muscle modeling that attempts to provide models for human musculature based on the real morphological structures. These models provide a good visual description of muscle form and action and represent a sound base from which to produce further progress toward medically accurate simulation of human bodies. Three major problems have been addressed: geometric modeling, deformation and texture. To allow for the wide variety of deformable muscle shapes encountered in the body, while retaining as many of their common properties as possible, the geometric models are classified into several categories according to the characteristics of their structures and actions. Within each category, the model for each muscle has an efficient structural form, created using anatomical data. Deformation is also performed on the basis of the categories, with all models within each category sharing the same deformation scheme. The categories cover both general and special cases. The result is an efficient, anatomically accurate muscle representation that is specifically designed to accommodate the particular form of deformation exhibited by each individual muscle. Interactions between muscles; are also taken into account to avoid penetration occurring between adjacent muscles in our model. To provide a suitable visual effect, the muscle texture is generated directly on the model surface. The textures and colors are obtained from anatomical data via image analysis. Some results are presented on the geometric modeling, the deformation and the texture of muscles related to the lower limb.

A virtual control environment for robot teleoperation via the Internet is presented. It comprises a Java3D-based real-time virtual representation of the robot and worksite, and uses a graphic panel, an environment for remote robot programming, and a dataglove with a 6D position tracker as the control interfaces. The use of virtual reality (VR) techniques for Internet teleoperation allow: (1) time delays inherent in IP networks to be suppressed and (2) the operator's work to be simplified and accelerated, compared to methods that use delayed TV images. The system realisation, with its use of open technologies Java, Java3D and 3-tier client/server architecture, provides portability among different computer platforms and types of robots. The efficiency of the VR-based methods developed has been verified for slow communication rates (0.1-0.5 KB/sec), where TV-based control methods are inapplicable. VR systems have been developed for the WWW-based control of the PUMA and CRS industrial robot manipulators. The particulars of these systems, the experiments undertaken, current issues, and directions of future work are presented.

Navigation path planning is a crucial part of virtual endoscopy, but the identification of the optimal fly-through path is a time-intensive process. This paper describes a prototype system for virtual endoscopy and proposes a slice-based approach to calculating the path of the virtual camera that uses the slice borderlines of region-of-interest images to obtain the approximate centreline, centralised locally with respect to the hollow object wall. By using the 2D slice borderlines to express the hollow object boundary, the path searching and polygon intersection computing are simplified and made more efficient. Finally, we present results of our algorithm tested on the Visible Human data set.

Presents a method concerning the volume rendering of fine details, such as blood vessels and nerves, from medical data. The realistic and efficient visualization of such structures is often of great medical interest, and conventional rendering techniques do not always deal with them adequately. Our method uses preprocessing to reconstruct fine details that are difficult to segment and label. It detects the presence of fine geometrical structures, such as cracks or cylinders that suggest the existence of, for example, blood vessels or nerves; the subsequent volume rendering then displays fine geometrical objects that lie on a surface. The method can also show structures within the volume, using a special "integration sampling" scheme to portray reconstructed volume texture, such as that exhibited by muscle fibers. By combining the surface structure and volume texture in the rendering, realistic results can be produced; examples are provided.

Muscle simulation should be an important component of human modelling, but to date there have been few attempts to demonstrate muscle structures in an anatomically-correct way. This paper proposes a feature-based approach to muscle modelling which attempts to provide models for human musculature based on the real anatomical structures. These models provide a good visual description and form a sound basis for further developments towards medically-accurate simulation of human bodies. To allow for the wide variety of muscle shapes encountered in the body, the geometric models are based on muscle features identified from radiological data. These results are realistic models with correct anatomical structures.

A methodology for modelling quadruped gaits and gait transitions based on Fourier series analysis of horse movement is proposed. The resultant model is used to create animated locomotion sequences of a quadruped changing gait. The dynamic similarity hypothesis is used as a method for comparing the gaits of different animals. The fields investigated to provide the background of this work are animation, gait research, data gathering and simulation. From these the methodology has been used to define a generic rotoscoped model for movement, which although developed from horse movement data, could be equally applied to any other quadruped. Keys ideas from biomechanics and gait research have been incorporated into the gait and gait transition models. Different gaits have fundamentally different leg movement patterns, so a locomotion model which models different gaits must take into account the synchronisation between the legs during locomotion. Additionally any methodology used to simulate the transition between gaits must take into account the phase differences between the legs when simulation a gait transition. Animation provides techniques to model the visual motion of a multi-legged figure moving using a number of different gaits, the control of movement is determined by the gait model.

Virtual environment (VE) techniques provide a powerful tool for the visualisation of the 3D environment of a teleoperation work site, particularly when "live" video display is inadequate for the task's operation or when its transmission is constrained, for example by limited bandwidth. However, the ability of a VE to cope with the dynamic phenomena of typical teleoperation work sites is severely limited by its pre-defined model-based nature. Thus, an online composing mechanism is needed to make it environment-compliant. This paper describes a method for this purpose, based on workspace analysis, in which objects are constructed from simple 2D images and VEs are modelled interactively. Experiments have shown that the method is convenient and effective for online VE editing.

Large‐sized volume datasets have recently become commonplace and users are now demanding that volume‐rendering techniques to visualise such data provide acceptable results on relatively modest computing platforms. The widespread use of the Internet for the transmission and/or rendering of volume data is also exerting increasing demands on software providers. Multiresolution can address these issues in an elegant way. One of the fastest volume‐rendering alrogithms is that proposed by Lacroute & Levoy 1 , which is based on shear‐warp factorisation and min‐max octrees (MMOs). Unfortunately, since an MMO captures only a single resolution of a volume dataset, this method is unsuitable for rendering datasets in a multiresolution form. This paper adapts the above algorithm to multiresolution volume rendering to enable near‐real‐time interaction to take place on a standard PC. It also permits the user to modify classification functions and/or resolution during rendering with no significant loss of rendering speed. A newly‐developed data structure based on the MMO is employed, the multiresolution min‐max octree, M 3 O, which captures the spatial coherence for datasets at all resolutions. Speed is enhanced by the use of multiresolution opacity transfer functions for rapidly determining and discarding transparent dataset regions. Some experimental results on sample volume datasets are presented.

A system for WWW-based remote robot tele-operation is presented. It addresses important problems of Internet telerobotics such as "how do we make the system reliable?", "how do we make the system fast?", and finally, "how do we make the system open and portable?". The recent open technologies Java and Java3D are used for developing the system. Key features of the system are: (1) the Java3D based "live" virtual representation of the real robot and its environment, and (2) the use of a powerful tool for the remote programming of the robot. Possible applications of the teleoperation tools developed and methods within VR are also briefly discussed.

The steady growth of the Internet has dramatically changed the way information is shared and modern users expect near real time delivery, high quality images together with in-depth navigation and exploration of 3D models. Multiresolution is a promising approach for fast distributed volume visualisation employing levels-of-detail. We review multiresolution algorithms and visualisation systems on the WWW. Our discussion is based on experience gained in the development of the IAEVA-II project funded by the European Commission. A new method for rapid data classification/rendering of multiresolution volumes based on shear-warp factorisation, is described. We can change classification functions and data resolution during rendering without significant reduction in interactivity. A method for constructing multiresolution transfer functions for determining opacity is also investigated. Finally, future trends in developing WWW visualisation systems are discussed.

The paper demonstrates how NURBS-based Free-Form Deformations (NFFDs) can be used to generate and sculpt NURBS based objects in a way that avoids many of the limitations of ordinary FFDs. A system is described in which the user interacts with the NFFD through a set of direct acting tools, removing the need to manipulate the mesh directly. As the user applies the tools to the object, the NFFD is updated automatically. Objects are represented as isosurfaces of the NFFD volume, giving a good insight into the way an NFFD would deform a general object.

Precise control of the shape of a flexible object during animation is a time-consuming task for the animator, for which there is, as yet, no universally-applicable method. This paper describes a system which provides improved support in this area. In the system, objects are modelled within a stereoscopic environment, and the user interfaces with the system via two hand-held devices, a SpaceBall and a mouse. The object is positioned and oriented by "holding" it in one hand, while the other hand employs the mouse to sculpt the object as if it were made of clay, using a "point and click" paradigm, rather than the conventional "pick and drag" approach. The object is sculpted at several pre-defined key positions before animation begins-these are defined parametrically, allowing animation of the object by interpolation in a straightforward way. To support this process and to ensure that the shape of the object remains sensible between the key positions, an extension to NURBS, called CISSes, has been developed. As a result of rests of a prototype system, the Basic CISS was further developed into the Cuboid CISS. The coherence of the object under animation can be mathematically demonstrated for the Cuboid CISS. This paper describes the Virtual Sculpting environment, the mathematical background of the CISS, and the results obtained using this approach for the animation of a limb. The final section identifies outstanding problems and future areas of work.

While parametric surfaces are most conveniently described by rectangular patches, most complex objects require the use of patches with other than four sides. Methods to generate such patches are widely used but all have drawbacks. This paper describes the creation of a surface which covers the original surface and the non-rectangular "hole" with a new, smooth surface. The method employs recursive splines and can be used with a control mesh of arbitrary topology. Control of the shape of the patch covering the "hole" can be achieved by user manipulation of a "controller" point on the patch.

Computer animators find that maintaining control of the shape of deformable objects during motion is sometimes difficult. This paper describes a system called "Gargoyle" which provides improved support in this area; it concentrates particularly on the form of interaction between user and computer. In Gargoyle, an object is sculpted at several predefined key positions which are associated with particular values of the parameters defining the surface. This allows the object to be animated by parametric interpolation in the conventional way. Within a two-handed stereoscopic environment, an object is modelled by "holding" it in one hand, while the other hand uses the mouse to sculpt the object (as if it were made of clay) using a "point-and-click" technique, rather than the conventional "pick-and-drag" approach. Several tools are available and, with each click of the mouse, the current tool is applied to the surface at the indicated point. The algorithms underlying the tools are outlined, and various objects which have been sculpted using them are described.

While parametric surfaces are most conveniently described by rectangular patches, most complex objects require the use of patches with other than four sides. Many methods to generate such patches are widely used, but all have drawbacks. The paper describes the creation of a surface which covers the original surface and the non-rectangular "hole" with a new smooth surface. The method employs the recursive splines described by Savva and Clapworthy (ibid., 1998) and can be used with a control mesh of arbitrary topology. Further control of the shape of the patch covering the "hole" can be achieved by user manipulation of a "controller" point on the patch.

A method is presented which is capable of capturing surfaces of arbitrary topology. Derived from standard bicubic B/spl acute/ezier patches, it "fills in" n-sided regions with four-sided patches. It is based on a recursive patch-midpoint subdivision algorithm on a rectangular framework of control points, which is then generalised to arbitrary control-point nets. At each step, a new set of points with more vertices and smaller faces than the original set of points is constructed, resulting in a smooth surface. This structure provides the foundation for a general method to construct a smooth surface where the structure contains non-rectangular patches.

We describe a research project for the development of a system for cataloguing, retrieval and interactive manipulation of 3D models of pathological human organs from a distributed WWW database. The project aims to provide transmission and rendering of three-dimensional models of human pathologies (constructed mainly from MRI and CT slices), enhanced manipulation and fly-through functionality on the models, as well as 3D animation sequences of virtual endoscopy. The system supports standard PC platforms without specialised hardware, thereby allowing accessibility to the widest possible audience. The system will provide the end users with advanced imaging capabilities such as models derived from multi-modal inputs (CT and MRI), stereoscopic display and will incorporate a number of features such as model warping. In addition to interactive utilisation, the service will provide interactive platforms for education, incorporating monitoring and assessment, as well as for information and/or counselling exchange between users.

The Internet provides an excellent facility both for disseminating medical information rapidly and for accumulating a coherent and widely available body of medical reference material, and the medical community has recently begun to tap its potential in a number of ways. The paper describes a service which is available on the WWW and which is designed to provide a 3D visualisation system to advance the education of medical students and the professional development of qualified medical practitioners. Particular reference is made to the type of graphical support demanded by such a system, and the feasibility of providing such a resource, taking into account the equipment currently available to the likely users. A discussion of related issues such as user requirements and medical standards is included, and possible future developments are identified.

The paper considers an efficient approach to traversing a uniformly‐subdivided space pierced by a line segment. A voxel, as the basic constituent element of the uniformly subdivided space, is restricted to having the form of a cube. The algorithm works in two steps. In the first step, the so‐called Bresenham voxels are identified and, by comparing their position codes, their type of connectivity is determined. To achieve the required connectivity between neighbouring voxels, the second step of the algorithm is applied to find the missing voxels. In this way, the algorithm efficiently switches between face‐, edge‐ and vertex‐connectivity. Although the algorithm works with oating‐point precision, it is extremely computationally efficient, and tests of speed compared with the Müller, Cleary & Wyvill, Amanatides & Woo, and Zemčik algorithms are described.

Abstract This paper presents the application of inverse Lagrangian dynamics for the purpose of animating articulated models. The method orginates from mechanics and robotics and has been adapted to deal with branched kinematic chains and joints with multiple degrees of freedom. The method is then reformulated to calculate the ground reaction forces that apply to the body. The approach is direct and does not involve guesswork. The formulation has been implemented into a general animation system that is entirely interactive and supports the facility of simulating generic articulated models.