Volume rendering is a technique for visualizing 3D arrays of sampled data. It has applications in areas such as medical imaging and scientific visualization, but its use has been limited by its high computational expense. Early implementations of volume rendering used brute-force techniques that require on the order of 100 seconds to render typical data sets on a workstation. Algorithms with optimizations that exploit coherence in the data have reduced rendering times to the range of ten seconds but are still not fast enough for interactive visualization applications. In this thesis we present a family of volume rendering algorithms that reduces rendering times to one second. First we present a scanline-order volume rendering algorithm that exploits coherence in both the volume data and the image. We show that scanline-order algorithms are fundamentally more efficient than commonly-used ray casting algorithms because the latter must perform analytic geometry calculations (e.g. intersecting rays with axis-aligned boxes). The new scanline-order algorithm simply streams through the volume and the image in storage order. We describe variants of the algorithm for both parallel and perspective projections and

Although information visualization (infovis) technologies have proven indispensable tools for making sense of complex data, wide-spread deployment has yet to take hold, as successful infovis applications are often difficult to author and require domain-specific customization. To address these issues, we have created prefuse, a software framework for creating dynamic visualizations of both structured and unstructured data. prefuse provides theoretically-motivated abstractions for the design of a wide range of visualization applications, enabling programmers to string together desired components quickly to create and customize working visualizations. To evaluate prefuse we have built both existing and novel visualizations testing the toolkit's flexibility and performance, and have run usability studies and usage surveys finding that programmers find the toolkit usable and effective.

We present a technique for large matrix-matrix multiplies using low cost graphics hardware. The result is computed by literally visualizing the computations of a simple parallel processing algorithm. Current graphics hardware technology has limited precision and thus limits immediate applicability of our algorithm. We include results demonstrating proof of concept, correctness, speedup, and a simple application. This is therefore forward looking research: a technique ready for technology on the horizon.

In this paper a stereo algorithm suitable for implementation on commodity graphics hardware is presented. This is important since it allows to free up the main processor for other tasks including high-level interpretation of the stereo results. Our algorithm relies on the traditional sum-of-square-differences (SSD) dissimilarity measure between correlation windows. To achieve good results close to depth discontinuities as well as on low texture areas a multiresolution approach is used. The approach efficiently combines SSD measurements for windows of different sizes. Our implementation running on an NVIDIA GeForce4 graphics card achieves 50-70M disparity evaluations per second including all the overhead to download images and read-back the disparity map, which is equivalent to the fastest commercial CPU implementations available. An important advantage of our approach is that rectification is not necessary so that correspondences can just as easily be obtained for images that contain the epipoles. Another advantage is that this approach can easily be extended to multi-baseline stereo.

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In this paper we present an adaptive approach to volume rendering via 3D textures at arbitrary levels of detail. The algorithm has been designed to enable interactive exploration of large-scale data sets while providing user-adjustable resolution levels. A texture map hierarchy is constructed in a way that minimizes the amount of texture memory with respect to the power-of-two restriction imposed by OpenGL implementations. In addition, our hierarchical levelof-detail representation guarantees consistent interpolation between different resolution levels. Special attention has been paid to the fixing of rendering artifacts that are introduced by non-corrected opacities at level transitions. By adapting the sample slice distance with regard to the desired level-of-detail, the number of texture lookups is reduced significantly.

this paper, we present an algorithm for general visibility queries. This algorithm exploits several OpenGL features in order to obtain faster results for large polygonal models. To show the applicability of our algorithm -- in terms of graphics performance -- on low-end graphics workstations, we performed all measurements on an SGI O2 /R10000 and an SGI Octane/MXE graphics workstation. Furthermore, we propose an extension to the OpenGL rendering pipeline to add features for improved general occlusion culling.

We develop a progressive refinement algorithm that generates an approximate image quickly, then gradually refines it towards the final result. Our algorithm can reconstruct a high-quality image after evaluating only a small percentage of the pixels. For a typical scene, evaluating only 6 % of the pixels yields an approximate image that is visually hard to distinguish from an image with all the pixels evaluated. At this low sampling rate, previous techniques such as adaptive stochastic sampling suffer from artifacts including heavily jagged edges, missing object parts, and missing high-frequency details. A key ingredient of our algorithm is the directional coherence map (DCM), a new technique for handling general radiance discontinuities in a progressive ray tracing framework. Essentially an encoding of the directional coherence in image space, the DCM performs well on discontinuities that are usually considered extremely difficult, e.g. those involving non-polygonal geometry or caused by secondary light sources. Incorporating the DCM into a ray tracing system incurs only a negligible amount of additional computation. More importantly, the DCM uses little memory and thus it preserves the strengths of ray tracing systems in dealing with complex scenes. We have implemented our algorithm on top of RADIANCE. Our enhanced system can produce high-quality images significantly faster than RADIANCE – sometimes by orders of magnitude. Moreover, when the baseline system becomes less effective as its Monte Carlo components are challenged by difficult lighting configurations, our system will still produce high quality images by redistributing computation to the small percentage of pixels as dictated by the DCM.

For applications in computer game development and character animation, recent work in behavioral animation has taken impressive steps toward autonomous, self-animating characters. It remains difficult, however, to direct autonomous characters to perform specific tasks. We propose a new approach to high-level control in which the user gives the character a behavior outline, or “sketch plan”. The behavior outline specification language has syntax deliberately chosen to resemble that of a conventional imperative programming language. In terms of functionality, however, it is a strict superset. In particular, a behavior outline need not be deterministic. This added freedom allows many behaviors to be specified more naturally, more simply, more succinctly and at a much higher-level than would otherwise be possible. The character has complete autonomy to decide on how to fill in the necessary missing details. The success of our approach rests heavily on our use of a rigorous logical language, known as the situation calculus. The situation calculus is well-known, simple and intuitive to understand. The basic idea is that a character views its world as a sequence of “snapshots ” known as situations. An understanding of how the world can change from one situation to another can then be given to the character by describing what the effect of performing each given action would be. The character can use this knowledge to keep track of its world and to work out which actions to do next in order to attain its goals. The version of the situation calculus we use incorporates a new approach to representing epistemic fluents. The approach is based on interval arithmetic and addresses a number of difficulties in implementing

In this paper we introduce a simple and efficient scheme for encoding the connectivity and the stripification of a triangle mesh. Since generating a good set of triangle strips is a hard problem, it is desirable to do this just once and store the computed strips with the triangle mesh. However, no previously reported mesh encoding scheme is designed to include triangle strip information into the compressed representation. Our algorithm encodes the stripification and the connectivity in an interwoven fashion, that exploits the correlation existing between the two. Key words: Mesh compression, connectivity encoding, triangle strips, triangle fans, stripification. 1