A mantra we've heard over the years is that the consumer gaming market drives graphics technology. Our thesis is that the same does not hold true for networking technology. Instead, it is applications from high performance graphics and visualization efforts, not games, that push networks past their breaking point, which in turn stimulates work that results in better networks. This case study shows how a high performance computational science and visualization application has set new levels of networking performance by winning the SC2001 Application Bandwidth Challenge by novel use of existing network protocols.

The very largest parallel particle simulations, for problems involving six dimensional phase space, generate vast quantities of data. It is desirable to store such enormous datasets efficiently and also to share data effortlessly between data analysis tools such as PartView~\cite FPAT082 and extensions to AVS/Express among other groups who are working on particle-based accelerator simulations. We define a very simple file schema built on top of HDF5~\cite hdf5hp (Hierarchical Data Format version 5) as well as an API that simplifies the reading/writing of the data to the HDF5 file format. HDF5 offers a self-describing machine-independent binary file format that supports scalable parallel I/O performance for MPI codes on computer systems ranging from laptops to supercomputers. The sample H5PartAPI is available for C, C++, and Fortran codes. The common file format will enable groups that using completely different simulation implementations to transparently share datasets and custom data analysis tools like Part View. We will show examples and benchmark data for various platforms.

The LBNL/NERSC Visportal effort explores ways to deliver advanced Remote/Distributed Visualization(RDV) capabilities through a Grid-enabled web-portal interface. The effort focuses on latency tolerant distributed visualization algorithms, GUI designs that are more appropriate for the capabilities of web interfaces, and refactoring parallel-distributed applications to work in a N-tiered component deployment strategy. Most importantly, our aim is to leverage commercially supported technology as much as possible in order to create a deployable, supportable, and hence viable platform for delivering grid-based visualization services to collaboratory users.

We discuss a web-based portal for the exploration, encapsulation, and dissemination of visualization results over the Grid. This portal integrates three components: an interface client for structured visualization exploration, a visualization web application to manage the generation and capture of the visualization results, and a centralized portal application server to access and manage grid resources. Our approach uses standard web technologies to make the system accessible with minimal user setup. We demonstrate the usefulness of the developed system using an example for Adaptive Mesh Refinement (AMR) data visualization.

Adaptive mesh refinement (AMR) is a numerical simulation technique used in computational fluid dynamics (CFD). By using a set of nested grids of different resolutions, AMR combines the simplicity of structu red rectilinear grids with the ability to adapt to local changes in complexity in th e domain. Without proper interpolation on the boundaries of grids of different lev els of a hierarchy, discontinuities can arise. Treating locations of data values giv en at cell centers of AMR grids as vertices of a dual grid creates gaps between hierarchy levels. Using an index-based tessellation approach that fills these gaps with ``stitch cells'' we define an interpolation scheme that avoids discontinuities at level boundaries. We use the resulting interpolation scheme to generate volume-rendered images. Modifying transfer functions on a per-level basis allows us to emphasize (or de-emphasize) a specific level and gain a better understanding of the underlying hierarchical structure.

The complexity of physical phenomena often varies substantially over space and time. There can be regions where a physical phenomenon/quantity varies very little over a large extent. At the same time, there can be small regions where the same quantity exhibits highly complex variations. Adaptive mesh refinement (AMR) is a technique used in computational fluid dynamics (CFD) to simulate phenomena with drastically varying scales concerning the complexity of the simulated variables. Using multiple nested grids of different resolutions, AMR combines the topological simplicity of structured-rectilinear grids, permitting efficient computation and storage, with the possibility to adapt grid resolutions in regions of complex behavior. We present methods for direct volume rendering of AMR data. Our methods utilize AMR grids directly for efficiency of the visualization process. We apply a hardware-accelerated rendering method to AMR data supporting interactive manipulation of color-transfer functions and viewing parameters. We also present a cell-projection-based rendering technique for AMR data.

Researchers doing scientific computations are attempting to accurately model physical phenomena. When these physical phenomena take place at a variety of different spatial and temporal scales it can be more efficient and accurate to model them at different levels of detail in an adaptive, hierarchical manner. We present a framework for visualizing adaptive, hierarchical computations- a conceptual framework and an implementation framework. Given that researchers have already defined a hierarchical structure for their data and are performing their computations using this structure, it has become important to provide a visualization tool which accurately represents this data and visualizes it directly. The tool we have designed for this purpose was built using the Visualization Toolkit, VTK, and one of its interpretive interfaces, Tcl/Tk. In addition to creating a visualization tool, we are developing extensions of visualiztion techniques and algorithms to hierarchiacal data (i.e., seamless isosurface generation).