Gerd Marmitt

B-KD trees for hardware accelerated ray tracing of dynamic scenes

This paper introduces a new spatial index structure, called Bounded KD tree (B-KD tree), for realtime ray tracing of dynamic scenes. By presenting hardware units of all time critical B-KD tree algorithms in the context of a custom realtime ray tracing chip we show that this spatial index structure is well suited for hardware implementation. B-KD trees are a hybrid spatial index structure that combine the advantages of KD trees and Bounding Volume Hierarchies into a single, simple to handle spatial index structure. Similar to KD trees, B-KD trees are binary trees where each node considers only a single spatial dimension. However, instead of a single splitting plane that divides space into two disjoint sub-spaces, each node in B-KD trees contains two pairs of axis aligned planes that bound the geometry of its two child nodes. As a bounding volume approach B-KD trees allow for simple and efficient updates when changing geometry while maintaining the fast traversal operations and simple hardware implementation known from KD trees. This enables the support for dynamic scenes with constant mesh topology and coherent dynamic changes, like typical skinned meshes. Our hardware architecture contains several fixed-function units that completely handle skinning, updating, and ray tracing of dynamic scenes using B-KD trees. An FPGA prototype of this architecture already delivers realtime performance of up to 35 frames per second even when clocked at only 66 MHz.

Faster isosurface ray tracing using implicit KD-trees

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 preintegrated volume rendering. However, these approaches have a number of limitations in terms of the 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.

Fast ray traversal of tetrahedral and hexahedral meshes for direct volume rendering

The importance of high-performance rendering of unstructured or curvilinear data sets has increased significantly, mainly due to its use in scientific simulations such as computational fluid dynamics and finite element computations. However, the unstructured nature of these data sets lead to rather slow implementations for ray tracing. The approaches discussed in this paper are fast and scalable towards realtime ray tracing applications. We evaluate new algorithms for rendering tetrahedral and hexahedral meshes. In each algorithm, the first cell along a ray is found using common realtime ray tracing techniques. For traversing subsequent cells within the volume, Plucker coordinates as well as ray-bilinear patch intersection tests are used. Since the volume is rendered directly, all algorithms are applicable for isosurface rendering, maximum-intensity projection, and emissionabsorption models.

Interactive Volume Rendering with Ray Tracing

Recent research on high-performance ray tracing has achieved rea l-time performance even for highly complex surface models already on a single PC. In this report we provide an over view of techniques for extending real-time ray tracing also to interactive volume rendering. We review fast rendering techniques for different volume representations and rendering modes in a variety of computing environments. T he physically-based rendering approach of ray tracing enables high image quality and allows for easily mixing surface, volume, and other primitives in a scene, while fully accounting for all of their optical interactions. We presen t optimized implementations and discuss the use of upcoming high-performance processors for volume ray tracing.

Interactive iso-surface ray tracing of massive volumetric data sets

The visualization of iso-surfaces from gridded volume data is an important tool in many scientific applications. Today, it is possible to ray trace high-quality iso-surfaces at interactive frame rates even on commodity PCs. However, current algorithms fail if the data set exceeds a certain size either because they are not designed for outof- core data sets or the loading times are too high because there is too much overhead involved in the out-of-core (OOC) techniques. We propose a kD-tree based OOC data structure that allows to ray trace iso-surfaces of large volumetric data sets of many giga bytes at interactive frame rates on a single PC. A LOD technique is used to bridge loading times of data that is fetched asynchronously in the background. Using this framework we are able to ray trace iso-surfaces between 2 and 4 fps on a single dual-core Opteron PC at 640×480 resolution and an in-core memory footprint that is only a fraction of the entire data size.

Efficient CPU-based Volume Ray Tracing Techniques

Recent research on high‐performance ray tracing has achieved real‐time performance even for highly complex surface models already on a single PC. In this report, we provide an overview of techniques for extending real‐time ray tracing also to interactive volume rendering. We review fast rendering techniques for different volume representations and rendering modes in a variety of computing environments. The physically‐based rendering approach of ray tracing enables high image quality and allows for easily mixing surface, volume and other primitives in a scene, while fully accounting for all of their optical interactions. We present optimized implementations and discuss the use of upcoming high‐performance processors for volume ray tracing.

Terrain Guided Multi-Level Instancing of Highly Complex Plant Populations

In this paper we demonstrate how todays ray tracing techniques can be applied to photo-realistically render extremely huge landscapes covered with trees and forests, where a user can freely choose between highly detailed close-up views or flyover scenarios. This is made possible by mapping a number of square sub-scenes onto a huge polygonal terrain during run-time. The full plant population results from the combination of these tiles, which are iterated over the terrain. This is demonstrated at the example of a highly complex, plant covered ecosystem containing trillions of triangles