The Experts below are selected from a list of 7902 Experts worldwide ranked by ideXlab platform
Charles Hansen - One of the best experts on this subject based on the ideXlab platform.
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interactive Isosurface ray tracing of large octree volumes
2006 IEEE Symposium on Interactive Ray Tracing, 2006Co-Authors: Aaron Knoll, Ingo Wald, Steven G. Parker, Charles HansenAbstract:We present a technique for ray tracing Isosurfaces of large compressed structured volumes. Data is first converted into a lossless-compression octree representation that occupies a fraction of the original memory footprint. An Isosurface is then dynamically rendered by tracing rays through a min/max hierarchy inside interior octree nodes. By embedding the acceleration tree and scalar data in a single structure and employing optimized octree hash schemes, we achieve competitive frame rates on common multicore architectures, and render large time-variant data that could not otherwise be accommodated
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Interactive display of Isosurfaces with global illumination
IEEE transactions on visualization and computer graphics, 2006Co-Authors: Chris Wyman, Steven G. Parker, Peter Shirley, Charles HansenAbstract:In many applications, volumetric data sets are examined by displaying Isosurfaces, surfaces where the data, or some function of the data, takes on a given value. Interactive applications typically use local lighting models to render such surfaces. This work introduces a method to precompute or lazily compute global illumination to improve interactive Isosurface renderings. The precompiled illumination resides in a separate volume and includes direct light, shadows, and intersections. Using this volume, interactive globally illuminated renderings of Isosurfaces become feasible while still allowing dynamic manipulation of lighting, viewpoint and isovalue.
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view dependent Isosurface extraction
IEEE Visualization, 1998Co-Authors: Yarden Livnat, Charles HansenAbstract:We propose a new approach to polygonal Isosurface extraction that is based on extracting only the visible portion of the Isosurface. The visibility tests are done in two phases. First, coarse visibility tests are performed in software to determine the visible cells. These tests are based on hierarchical tiles and shear-warp factorization. The second phase resolves the visible portions of the extracted triangles and is accomplished by the graphics hardware. While the latest Isosurface extraction methods have effectively eliminated the search phase bottleneck, the cost of constructing and rendering the Isosurface remains high. Many of today's large datasets contain very large and complex Isosurfaces that can easily overwhelm even state-of-the-art graphics hardware. The proposed approach is output sensitive and is thus well suited for remote visualization applications where the extraction and rendering phases are done on a separate machines.
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IEEE Visualization - View dependent Isosurface extraction
Proceedings Visualization '98 (Cat. No.98CB36276), 1Co-Authors: Yarden Livnat, Charles HansenAbstract:We propose a new approach to polygonal Isosurface extraction that is based on extracting only the visible portion of the Isosurface. The visibility tests are done in two phases. First, coarse visibility tests are performed in software to determine the visible cells. These tests are based on hierarchical tiles and shear-warp factorization. The second phase resolves the visible portions of the extracted triangles and is accomplished by the graphics hardware. While the latest Isosurface extraction methods have effectively eliminated the search phase bottleneck, the cost of constructing and rendering the Isosurface remains high. Many of today's large datasets contain very large and complex Isosurfaces that can easily overwhelm even state-of-the-art graphics hardware. The proposed approach is output sensitive and is thus well suited for remote visualization applications where the extraction and rendering phases are done on a separate machines.
Yarden Livnat - One of the best experts on this subject based on the ideXlab platform.
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Shadows for Incomplete Point-based Isosurfaces
2005Co-Authors: Yarden Livnat, Xavier TricocheAbstract:This paper presents a method for computing shadows on incomplete point-based Isosurfaces. Such surfaces are obtained in our setting by a view-dependent Isosurface extraction method that allows interactive exploration of large scale datasets on commodity hardware. This approach raises the need for a novel and ecient technique to generate high-quality shadows. The latter dramatically enhances the realism of the visualized Isosurface and provides essential cues to perceive depth and small features of the geometry.
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Fast Isosurface extraction methods for large image data sets
Handbook of Medical Imaging, 2000Co-Authors: Yarden Livnat, Steven G. Parker, Chris R. JohnsonAbstract:We present fast Isosurface extraction methods for large imaging data sets. Specifically, we discuss three different Isosurface extraction techniques, which are appropriate for different visualization scenarios. The first technique is the Near Optimal Isosurface Extraction (NOISE) algorithm for rapidly extracting Isosurfaces. Using a new representation, termed the span space, of the underlying domain, we develop an Isosurface extraction algorithm with a worst case complexity of O( p n + k) for the search phase, where n is the size of the data set and k is the number of cells in the Isosurface. The memory requirement is kept at O(n) while the preprocessing step is O(n logn). While algorithms such as NOISE have effectively eliminated the search phase bottleneck, the cost of constructing and rendering the Isosurface remains high. Many of today’s large imaging data sets contain very large and complex Isosurfaces that can easily overwhelm even state-of-the-art graphics hardware. As such, we discuss an output sensitive algorithm that is based on extracting only the visible portion of the Isosurface. The previous two algorithms aim to extract explicit geometric primitives for the underlying Isosurface. However, it is sometimes unnecessary (and costly) to extract explicit geometry. We introduce an interactive isosurfacing method for very large imaging data sets with brute-force ray tracing on a conventional (distributed) shared-memory multiprocessor machine. Rather than generate geometry representing the Isosurface and render with a z-buffer, for each pixel we trace a ray through a volume and do an analytic Isosurface intersection computation. Although this method has a high intrinsic computational cost, its simplicity and scalability facilitate interactive exploration of large data sets on current high-end systems.
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view dependent Isosurface extraction
IEEE Visualization, 1998Co-Authors: Yarden Livnat, Charles HansenAbstract:We propose a new approach to polygonal Isosurface extraction that is based on extracting only the visible portion of the Isosurface. The visibility tests are done in two phases. First, coarse visibility tests are performed in software to determine the visible cells. These tests are based on hierarchical tiles and shear-warp factorization. The second phase resolves the visible portions of the extracted triangles and is accomplished by the graphics hardware. While the latest Isosurface extraction methods have effectively eliminated the search phase bottleneck, the cost of constructing and rendering the Isosurface remains high. Many of today's large datasets contain very large and complex Isosurfaces that can easily overwhelm even state-of-the-art graphics hardware. The proposed approach is output sensitive and is thus well suited for remote visualization applications where the extraction and rendering phases are done on a separate machines.
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A near optimal Isosurface extraction algorithm using the span space
IEEE Transactions on Visualization and Computer Graphics, 1996Co-Authors: Yarden Livnat, Han-wei Shen, Chris R. JohnsonAbstract:Presents the "Near Optimal Isosurface Extraction" (NOISE) algorithm for rapidly extracting Isosurfaces from structured and unstructured grids. Using the span space, a new representation of the underlying domain, we develop an Isosurface extraction algorithm with a worst case complexity of o(/spl radic/n+k) for the search phase, where n is the size of the data set and k is the number of cells intersected by the Isosurface. The memory requirement is kept at O(n) while the preprocessing step is O(n log n). We utilize the span space representation as a tool for comparing Isosurface extraction methods on structured and unstructured grids. We also present a fast triangulation scheme for generating and displaying unstructured tetrahedral grids.
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IEEE Visualization - View dependent Isosurface extraction
Proceedings Visualization '98 (Cat. No.98CB36276), 1Co-Authors: Yarden Livnat, Charles HansenAbstract:We propose a new approach to polygonal Isosurface extraction that is based on extracting only the visible portion of the Isosurface. The visibility tests are done in two phases. First, coarse visibility tests are performed in software to determine the visible cells. These tests are based on hierarchical tiles and shear-warp factorization. The second phase resolves the visible portions of the extracted triangles and is accomplished by the graphics hardware. While the latest Isosurface extraction methods have effectively eliminated the search phase bottleneck, the cost of constructing and rendering the Isosurface remains high. Many of today's large datasets contain very large and complex Isosurfaces that can easily overwhelm even state-of-the-art graphics hardware. The proposed approach is output sensitive and is thus well suited for remote visualization applications where the extraction and rendering phases are done on a separate machines.
Han-wei Shen - One of the best experts on this subject based on the ideXlab platform.
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PacificVis - Visualizing the variations of ensemble of Isosurfaces
2016 IEEE Pacific Visualization Symposium (PacificVis), 2016Co-Authors: Subhashis Hazarika, Soumya Dutta, Han-wei ShenAbstract:Visualizing the similarities and differences among an ensemble of Isosurfaces is a challenging problem mainly because the Isosurfaces cannot be displayed together at the same time. For ensemble of Isosurfaces, visualizing these spatial differences among the surfaces is essential to get useful insights as to how the individual ensemble simulations affect different Isosurfaces. We propose a scheme to visualize the spatial variations of Isosurfaces with respect to statistically significant Isosurfaces within the ensemble. Understanding such variations among ensemble of Isosurfaces at different spatial regions is helpful in analyzing the influence of different ensemble runs over the spatial domain. In this regard, we propose an Isosurface-entropy based clustering scheme to divide the spatial domain into regions of high and low Isosurface variation. We demonstrate the efficacy of our method by successfully applying it on real-world ensemble data sets from ocean simulation experiments and weather forecasts.
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Evaluating Isosurfaces with level-set-based information maps
Computer Graphics Forum, 2013Co-Authors: Tzu-hsuan Wei, Teng-yok Lee, Han-wei ShenAbstract:While Isosurfaces have been widely used for scalar data visualization, it is often difficult to determine if the selected Isosurfaces for visualization are sufficient to represent the entire scalar field. In this paper, we present an information-theoretic approach to evaluate the representativeness of a given Isosurface set. Our basic idea is that given two Isosurfaces that enclose a subvolume, if the intermediate Isosurfaces in the subvolume can be generated by smoothly morphing from one Isosurface to the other, no additional Isosurfaces are needed since the geometry of the true Isosurfaces within the subvolume can be easily inferred. To realize this idea, given a pair of Isosurfaces, to determine if such a smooth condition in the enclosed region is satisfied, we use a level-set approach to generate the intermediate surfaces. On each intermediate surface, we sample the values from the scalar field and exam the distribution. If the entropy of the distribution is low, this intermediate surface is aligned well with a true Isosurface in the scalar field. For the intermediate surfaces generated by the level-set method from the boundary Isosurfaces, the distributions of scalar values from the level-set surfaces form a 2D distribution, called Isosurface information map. This information map can be used as an indicator of the representativeness of the boundary Isosurfaces for the data in the subregion, allowing a quantitative measurement of information representable by the input Isosurfaces. Based on this information-theoretic approach, this paper presents an Isosurface selection algorithm that can automatically select Isosurfaces for more effective visualization of scalar fields.
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parallel view dependent Isosurface extraction using multi pass occlusion culling
Parallel and Large-Data Visualization and Graphics 2001. Proceedings. IEEE 2001 Symposium on, 2009Co-Authors: Jinzhu Gao, Han-wei ShenAbstract:This paper presents a parallel algorithm that can effectively extracts only the visible portion of Isosurfaces. The main focus of our research is to devise a load-balanced and output-sensitive algorithm, that is, each processor will generate approximately the same amount of triangles, and cells that do not contain the visible Isosurface will not be visited. A novel multi-pass algorithm is proposed in the paper to achieve these goals. In the algorithm, we first use an octree data structure to rapidly skip the empty cells. An image space visibility culling technique is then used to identify the visible Isosurface cells in a progressive manner. To distribute the workload, we use a binary image space partitioning method to ensure that each processor will generate approximately the same amount of triangles. Isosurface extraction and visibility update are performed in parallel to reduce the total computation time. In addition to reducing the size of output geometry and accelerating the process of Isosurface extraction, the multi-pass nature of our algorithm can also be used to perform time-critical computation.
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interactive exploration of remote Isosurfaces with point based non photorealistic rendering
IEEE Pacific Visualization Symposium, 2008Co-Authors: Han-wei Shen, Jinzhu GaoAbstract:We present a non-photo realistic rendering technique for interactive exploration of Isosurfaces generated from remote volumetric data. Instead of relying on the conventional smooth shading technique to render the Isosurfaces, a point-based technique is used to represent and render the Isosurfaces in a remote client-server environment. The non-photo realistic nature of the proposed rendering method enables the server to transmit only the essential surface features, which substantially reduces the network traffic. The algorithm also utilizes frame coherence and efficiently encodes the Isosurface configuration inside each voxel cell to further minimize the network overhead. Finally, our algorithm can adjust the point distributions using different illumination settings to adapt to different network speeds.
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The Visualization Handbook - 3 – Time-Dependent Isosurface Extraction
Visualization Handbook, 2005Co-Authors: Han-wei ShenAbstract:To analyze complex dynamic phenomena from a time-varying data-set, it is necessary to navigate and browse the data in both the spatial and the temporal domain, select data at different resolutions, experiment with different visualization parameters, and compute and animate selected features over a period of time. To facilitate exploratory visual data analysis, it is very important that the visualization software is able to compute, animate, and track desired features at an interactive speed. This chapter discusses the topic of Isosurface extraction for time-varying data. The chapter begins with discussing two Isosurface cell search data structures that can minimize the storage overhead while keeping the search performance high. The chapter then discusses the work on extracting time-varying Isosurfaces in 4D space that allows for smooth animation of Isosurfaces in time. These high-dimensional Isosurface extraction algorithms can also provide several additional benefits such as computing the Isosurface envelopes and interval volumes.
Kenneth I. Joy - One of the best experts on this subject based on the ideXlab platform.
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compression and occlusion culling for fast Isosurface extraction from massive datasets
Mathematical Foundations of Scientific Visualization Computer Graphics and Massive Data Exploration, 2009Co-Authors: Benjamin F Gregorski, J Senecal, Mark A Duchaineau, Kenneth I. JoyAbstract:We present two algorithms for data compression and occlusion culling that im- prove interactive, adaptive Isosurface extraction from large volume datasets. Our algorithm, based on hierarchical tetrahedral meshes defined by longest edge bisection, allows arbitrary Isosurfaces to be adaptively extracted at interactive rates from losslessly compressed volumes where the region of interest, determined at runtime by user interaction, is decompressed on- the-fly. For interactive applications, we exploit frame-to-frame coherence between consecutive views to simplify the mesh structure in occluded regions and eliminate occluded triangles sig- nificantly reducing the complexity of the visualized surface and the underlying multiresolution volume representation. We extend the use of hardware accelerated occlusion queries to adap- tive Isosurface extraction applications where the surface geometry and topology change with the level-of-detail and view-point and the user can select an arbitrary isovalue for visualization.
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Using Difference Intervals for Time-Varying Isosurface Visualization
IEEE transactions on visualization and computer graphics, 2006Co-Authors: K.w. Waters, Kenneth I. JoyAbstract:We present a novel approach to out-of-core time-varying Isosurface visualization. We attempt to interactively visualize time-varying datasets which are too large to fit into main memory using a technique which is dramatically different from existing algorithms. Inspired by video encoding techniques, we examine the data differences between time steps to extract Isosurface information. We exploit span space extraction techniques to retrieve operations necessary to update Isosurface geometry from neighboring time steps. Because only the changes between time steps need to be retrieved from disk, I/O bandwidth requirements are minimized. We apply temporal compression to further reduce disk access and employ a point-based previewing technique that is refined in idle interaction cycles. Our experiments on computational simulation data indicate that this method is an extremely viable solution to large time-varying Isosurface visualization. Our work advances the state-of-the-art by enabling all Isosurfaces to be represented by a compact set of operations
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iso splatting a point based alternative to Isosurface visualization
Pacific Conference on Computer Graphics and Applications, 2003Co-Authors: Bernd Hamann, Kenneth I. JoyAbstract:We present a new approach to Isosurface visualization that we call "iso-splatting." We use point primitives for representing and rendering Isosurfaces. The method consists of two steps. In the first step, point samples are generated throughout the volumetric domain of a scalar function. In the second step, these points are projected onto the Isosurface of interest. We render the resulting point set using a surface splatting algorithm. The method can be extended to out-of-core or parallel environments. Our results show that this method can offer much greater time and space efficiency when compared with standard triangle-based methods, thereby supporting higher levels of interactivity. Parts of the algorithm can be accelerated using graphics hardware. One key advantage of this approach is that, since extraction computations are divided into two smaller phases, work can be distributed to exploit all available resources.
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Hierarchical Isosurface Segmentation Based on Discrete Curvature
2003Co-Authors: Fabien Vivodtzev, Bernd Hamann, Lars Linsen, Kenneth I. Joy, Georges-pierre Bonneau, Bruno A. OlshausenAbstract:A high-level approach to describe the characteristics of a surface is to segment it into regions of uniform curvature behavior and construct an abstract representation given by a (topology) graph. We propose a surface segmentation method based on discrete mean and Gaussian curvature estimates. The surfaces are obtained from three-dimensional imaging data sets by Isosurface extraction after data presmoothing and postprocessing the Isosurfaces by a surface-growing algorithm. We generate a hierarchical multiresolution representation of the Isosurface. Segmentation and graph generation algorithms can be performed at various levels of detail. At a coarse level of detail, the algorithm detects the main features of the surface. This low-resolution description is used to determine constraints for the segmentation and graph generation at the higher resolutions. We have applied our methods to MRI data sets of human brains. The hierarchical segmentation framework can be used for brainmapping purposes.
Laura J Juszczak - One of the best experts on this subject based on the ideXlab platform.
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the broken ring reduced aromaticity in lys trp cations and high ph tautomer correlates with lower quantum yield and shorter lifetimes
Journal of Physical Chemistry B, 2014Co-Authors: Azaria S Eisenberg, Laura J JuszczakAbstract:Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state Isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK1, pK2, and pKR) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, Isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the 1La transition dipole moment. Where quantum yield is low, Isosurface charge distri...
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the broken ring reduced aromaticity in lys trp cations and high ph tautomer correlates with lower quantum yield and shorter lifetimes
The Journal of Physical Chemistry, 2014Co-Authors: Azaria S Eisenberg, Laura J JuszczakAbstract:Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state Isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK₁, pK₂, and pKR) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, Isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the ¹Lₐ transition dipole moment. Where quantum yield is low, Isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp quantum yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the Isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished quantum yield in proteins as well. Thus tryptophan ground state Isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes.