Jason D. Wood

Distributed and Collaborative Visualization

Visualization is a powerful tool for analyzing data and presenting results in science, engineering and medicine. This paper reviews ways in which it can be used in distributed and/or collaborative environments. Distributed visualization addresses a number of resource allocation problems, including the location of processing close to data for the minimization of data traffic. The advent of the Grid Computing paradigm and the link to Web Services provides fresh challenges and opportunities for distributed visualization—including the close coupling of simulations and visualizations in a steering environment. Recent developments in collaboration have seen the growth of specialized facilities (such as Access Grid) which have supplemented traditional desktop video conferencing using the Internet and multicast communications. Collaboration allows multiple users—possibly at remote sites—to take part in the visualization process at levels which range from the viewing of images to the shared control of the visualization methods. In this review, we present a model framework for distributed and collaborative visualization and assess a selection of visualization systems and frameworks for their use in a distributed or collaborative environment. We also discuss some examples of enabling technology and review recent work from research projects in this field.

Visualization in Grid Computing Environments

Grid computing provides a challenge for visualization system designers. In this research, we evolve the dataflow concept to allow parts of the visualization process to be executed remotely in a secure and seamless manner. We see dataflow at three levels: an abstract specification of the intent of the visualization; a binding of these abstract modules to a specific software system; and then a binding of software to processing and other resources. We develop an XML application capable of describing visualization at the three levels. To complement this, we have implemented an extension to a popular visualization system, IRIS Explorer, which allows modules in a dataflow pipeline to run on a set of grid resources. For computational steering applications, we have developed a library that allows a visualization system front-end to connect to a simulation running remotely on a grid resource. We demonstrate the work in two applications: the dispersion of a pollutant under different wind conditions; and the solution of a challenging numerical problem in elastohydrodynamic lubrication.

Visualization over the World Wide Web and its application to environmental data

Explores the way in which data visualization systems, in particular modular visualization environments, can be used over the World Wide Web. The conventional approach is for the publisher of the data also to be responsible for creating the visualization, and posting it as an image on the Web. This leaves the viewer in a passive role, with no opportunity to analyse the data in any way. We look at different scenarios that occur as we transfer more responsibility for the creation of the visualization to the viewer, allowing visualization to be used for analysis as well as presentation. We have implemented one particular scenario, where the publisher mounts the raw data on the Web, and the viewer accesses this data through a modular visualization environment-in this case, IRIS Explorer. The visualization system is hosted by the publisher, but its fine control is the responsibility of the viewer. The picture is returned to the viewer as VRML, for exploration via a VRML viewer such as Webspace. We have applied this to air quality data which is posted on the Web hourly: through our system, the viewer selects what data to look at (e.g. species of pollutant, location, time period) and how to look at it-at any time and from anywhere on the Web.

Recent Advances in Volume Visualization

In the past few years, there have been key advances in the three main approaches to the visualization of volumetric data: isosurfacing, slicing and volume rendering, which together make up the field of volume visualization.

Virtual reality Powerwall versus conventional microscope for viewing pathology slides: an experimental comparison.

Aims:  Virtual slides could replace the conventional microscope. However, it can take 60% longer to make a diagnosis with a virtual slide, due to the small display size and inadequate user interface of current systems. The aim was to create and test a virtual reality (VR) microscope using a Powerwall (a high‐resolution array of 28 computer screens) for viewing virtual slides more efficiently.

A Web Services Architecture for Visualization

Service-oriented architectures are increasingly being used as the architectural style for creating large distributed computer applications. This paper examines the provision of visualization as a service that can be made available to application designers in order to combine with other services. We develop a three-layer architecture: a client layer which provides the user interface; a stateful Web service middleware layer which provides a published interface to the visualization system; and finally, a visualization component layer which provides the core functionality of visualization techniques. This separation of middleware from the visualization components is crucial: it allows us to exploit the strengths of Web service technologies in providing standardized access to the system, and in maintaining state information throughout a session, but also gives us the freedom to build our visualization layer in an efficient and flexible way without the constraints of Web service protocols. We describe the design of a visualization service based on this architecture, and illustrate one aspect of the work by re-visiting an early example of Web-based visualization.

A Distributed Co-Operative Problem Solving Environment

Scientific research is often multidisciplinary in nature and hence large projects are frequently collaborative with participants from several separate research centres. Rather than being restricted to infrequent dissemination of results and meetings a framework is described for embedding scientific computing applications within a collaborative problem solving environment. This allows users to combine their expertise in an interactive visual environment. Separate users can collaboratively steer and visualize data from a numerical simulation by embedding the simulation within the IRIS Explorer visualization system. By making use of this system the user has access to the COVISA toolkit which facilitates collaboration between separate users of IRIS Explorer. The flexibility of this system makes it straightforward to visualize and control as many aspects of the solution process as are desired.

Using high-resolution displays for high-resolution cardiac data

The ability to perform fast, accurate, high-resolution visualization is fundamental to improving our understanding of anatomical data. As the volumes of data increase from improvements in scanning technology, the methods applied to visualization must evolve. In this paper, we address the interactive display of data from high-resolution magnetic resonance imaging scanning of a rabbit heart and subsequent histological imaging. We describe a visualization environment involving a tiled liquid crystal display panel display wall and associated software, which provides an interactive and intuitive user interface. The oView software is an OpenGL application that is written for the VR Juggler environment. This environment abstracts displays and devices away from the application itself, aiding portability between different systems, from desktop PCs to multi-tiled display walls. Portability between display walls has been demonstrated through its use on walls at the universities of both Leeds and Oxford. We discuss important factors to be considered for interactive two-dimensional display of large three-dimensional datasets, including the use of intuitive input devices and level of detail aspects.

A Parallel Grid Based PSE for EHL Problems

In this paper we explain how a Problem Solving Environment (PSE) can be constructed such that the computationally intensive sections are run using resources on the Computational Grid, operating remotely from the machine running the visualisation. The PSE in question is one solving demanding elastohydrodynamic lubrication problems from mechanical engineering. The numerical calculation is done here using both multilevel techniques and using parallelism. The global nature of the equation system behind the problem means that, given that this is a communications intensive calculation, the code scales remarkably well.

Volume Graphics and the Internet

The Internet has changed the face of computing. The use of e-mail and desktop video-conferencing has made collaboration between people very easy and very natural. Application-sharing technology, such as that provided by Microsoft’s NetMeeting, allows a single application to be accessed by a group of people at different locations. The Internet likewise enables collaboration between computers — the Distributed.net activity [1] harnesses spare computing power on the Internet to tackle mathematical tasks that otherwise could hardly be contemplated.