For almost two decades researchers have argued that ray tracing will eventually become faster than the rasterization technique that completely dominates todays graphics hardware. However, this has not happened yet. Ray tracing is still exclusively being used for off-line rendering of photorealistic images and it is commonly believed that ray tracing is simply too costly to ever challenge rasterization-based algorithms for interactive use. However, there is hardly any scientific analysis that supports either point of view. In particular there is no evidence of where the crossover point might be, at which ray tracing would eventually become faster, or if such a point does exist at all.

model (78K triangles). c) Animated wind-up toys (11K triangles) walking and jumping incoherently around each other. d) A rigid-body dynamics simulation of marbles (8.8K triangles). e) A complex scene of 174K animated triangles, where a fairy and a dragonfly dance through an animated forest. Scenes are rebuilt from scratch every frame, allowing fully dynamic animation. Including shading, texturing, and hard shadows, as used in the above images, we can render these scenes at 1024 × 1024 pixels with 15.3, 7.8, 10.2, 26.2, and 1.4 frames per second on a dual 3.2 GHz Xeon. Excluding shading, texturing, and shadows, we achieve 34.5, 15.8, 29.3, 57.1, and 3.4 frames per second. We present a new approach to interactive ray tracing of moderatesized animated scenes based on traversing frustum-bounded packets of coherent rays through uniform grids. By incrementally computing the overlap of the frustum with a slice of grid cells, we accelerate grid traversal by more than a factor of 10, and achieve ray tracing performance competitive with the fastest known packet-based kd-tree ray tracers. The ability to efficiently rebuild the grid on every frame enables this performance even for fully dynamic scenes that typically challenge interactive ray tracing systems. 1 Introduction and Related

Many disciplines must handle the creation, visualization, and manipulation of huge and complex 3D environments. Examples include large structural and mechanical engineering projects dealing with entire cars, ships, buildings, and processing plants. The complexity of such models is usually far beyond the interactive rendering capabilities of todays 3D graphics hardware. Previous approaches relied on costly preprocessing for reducing the number of polygons that need to be rendered per frame but suffered from excessive precomputation times --- often several days or even weeks.

The Temporal Branch-on-Need Tree (T-BON) extends the threedimensional branch-on-need octree for time-varying isosurface extraction. At each time step, only those portions of the tree and data necessary to construct the current isosurface are read from disk. This algorithm can thus exploit the temporal locality of the isosurface and, as a geometric technique, spatial locality between cells in order to improve performance. Experimental results demonstrate the performance gained and memory overhead saved using this technique. Keywords: isosurface, time-dependent scalar field visualization, multiresolution methods, octree 1 Introduction Isosurface extraction is an important technique for visualizing volumetric data. By exposing contours of constant value, isosurfaces provide a mechanism for understanding the structure of a scalar field. This method has been used effectively in several disciplines, including medicine [12, 18], computational fluid dynamics (CFD) [6, 7], and molecular dynam...

This paper presents an end-to-end, low-cost solution for visualizing time-varying volume data rendered on a parallel computer located at a remote site. Pipelining and careful grouping of processors are used to hide I/O time and to maximize processors utilization. Compression is used to significantly cut down the cost of transferring output images from the parallel computer to a display device through a wide-area network. This complete rendering pipeline makes possible highly efficient rendering and remote viewing of high resolution time-varying data sets in the absence of high-speed network and parallel I/O support. To study the performance of this rendering pipeline and to demonstrate high-performance remote visualization, tests were conducted on a PC cluster in Japan as well as an SGI Origin 2000 operated at the NASA Ames Research Center with the display located at UC Davis. Keywords: High Performance Computing, Image Compression, Parallel Volume Rendering, Pipelining, Remote Visualization, Scientific Visualization, Time-Varying Data, Wide-Area Network 1

Figure 1: Richtmyer-Meshkov Instability time steps:0,45,180,270. With 32 Linux PCs we are able to isosurface the full resolution 7.5 GB volume on the left at 6.7 frames per second and on the right at 2.1 frames per second. We have constructed a distributed parallel ray tracing system that interactively produces isosurface renderings from large data sets on a cluster of commodity PCs. The program was derived from the SCI Institute’s interactive ray tracer (*-Ray), which utilizes small to large shared memory platforms, such as the SGI Origin series, to interact with very large-scale data sets. Making this approach work efficiently on a cluster requires attention to numerous system-level issues, especially when rendering data sets larger than the address space of each cluster node. The rendering engine is an image parallel ray tracer with a supervisor/workers organization. Each node in the cluster runs a multi-threaded application. A minimal abstraction layer on top of TCP links the nodes, and enables asynchronous message handling. For large volumes, render threads obtain data bricks on demand from an object-based software distributed shared memory. Caching improves performance by reducing the amount of data transfers for a reasonable working set size. For large data sets, the cluster-based interactive ray tracer performs comparably with an SGI Origin system. We examine the parameter space of the renderer and provide experimental results for interactive rendering of large (7.5 GB) data sets.

We describe a new dynamic level-of-detail (LOD) technique that allows real-time rendering of large tetrahedral meshes. Unlike approaches that require hierarchies of tetrahedra, our approach uses a subset of the faces that compose the mesh. No connectivity is used for these faces so our technique eliminates the need for topological information and hierarchical data structures. By operating on a simple set of triangular faces, our algorithm allows a robust and straightforward graphics hardware (GPU) implementation. Because the subset of faces processed can be constrained to arbitrary size, interactive rendering is possible for a wide range of data sets and hardware configurations.

As computational engineering and science applications have grown in size and complexity, the process of analyzing and visualizing the resulting vast amounts of data has become an increasingly difficult task. Traditionally, data analysis and visualization are performed as post-processing steps after a simulation has been run. As simulations have increased in size, this task has become increasingly difficult--often requiring significant computation, high-performance machines, high capacity storage, and high bandwidth networks. Computational steering is an emerging technology that addresses this problem by "closing the loop" and providing a mechanism for integrating modeling, simulation, data analysis, and visualization. This integration allows a researcher to interactively control simulations and perform data analysis while avoiding many of the pitfalls associated with the traditional batch/post processing cycle. In this paper, we describe the application of interactive simulation and v...

Figure 1: Images generated using interactive ray tracing. From left to right, time step 225 of a Richtmyer-Meshkov instability simulation from

Abstract — The visualization of high-quality isosurfaces at interactive rates is an important tool in many simulation and visualization applications. Today, isosurfaces are most often visualized by extracting a polygonal approximation that is then rendered via graphics hardware, or by using a special variant of pre-integrated volume rendering. However, these approaches have a number of limitations in terms of quality of the isosurface, lack of performance for complex data sets, or supported shading models. An alternative isosurface rendering method that does not suffer from these limitations is to directly ray trace the isosurface. However, this approach has been much too slow for interactive applications unless massively parallel shared-memory supercomputers have been used. In this paper, we implement interactive isosurface ray tracing on commodity desktop PCs by building on recent advances in real-time ray tracing of polygonal scenes, and using those to improve isosurface ray tracing performance as well. The high performance and scalability of our approach will be demonstrated with several practical examples, including the visualization of highly complex isosurface data sets, the interactive rendering of hybrid polygonal/isosurface scenes including high-quality ray traced shading effects, and even interactive global illumination on isosurfaces. Index Terms — Ray tracing, real-time rendering, isosurface, visualization, global illumination 1