VisSym02: Joint Eurographics - IEEE TCVG Symposium on Visualization

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https://diglib.eg.org/handle/10.2312/403

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Cell-Based First-Hit Ray Casting
(The Eurographics Association, 2002) Neubauer, A.; Mroz, L.; Hauser, H.; Wegenkittl, R.; D. Ebert and P. Brunet and I. Navazo
Cell-based first-hit ray casting is a new technique for fast perspective volume visualization. This technique, based on the well known ray casting algorithm, performs iso-surfacing and supports interactive threshold adjustment. It is accelerated by the reduction of average ray path lengths to only a few steps per pixel. The volume is divided into cubic sub volumes. Each sub volume that is intersected by an iso-surface is projected to the image plane. A local ray casting step within the sub volume is performed for each pixel covered by the projection. Cell-based first-hit ray casting is perfectly suited whenever fast perspective iso-surfacing is required. This paper describes the basic algorithm, presents possible optimizations and evaluates the performance of the algorithm for one specific application, the post-implantation assessment of endovascular stent placement. It will be shown that the algorithm, though executed on a single processor machine without any hardware acceleration, performs well for view points inside as well as outside the stented blood vessel and significantly outperforms an optimized, yet more conventional ray casting technique.
Best Quadratic Spline Approximation for Hierarchical Visualization
(The Eurographics Association, 2002) Wiley, D. F.; Childs, H. R.; Hamann, B.; Joy, K. I.; Max, N. L.; D. Ebert and P. Brunet and I. Navazo
We present a method for hierarchical data approximation using quadratic simplicial elements for domain decomposition and field approximation. Higher-order simplicial elements can approximate data better than linear elements. Thus, fewer quadratic elements are required to achieve similar approximation quality. We use quadratic basis functions and compute best quadratic simplicial spline approximations that are C0-continuous everywhere. We adaptively refine a simplicial approximation by identifying and bisecting simplicial elements with largest errors. It is possible to store multiple approximation levels of increasing quality. We have tested the suitability and efficiency of our hierarchical data approximation scheme by applying it to several data sets.
An Open Toolkit for Prototyping Reverse Engineering Visualizations
(The Eurographics Association, 2002) Telea, Alexandru; Maccari, Alessandro; Riva, Claudio; D. Ebert and P. Brunet and I. Navazo
Maintenance and evolution of complex software systems (such as mobile telephones) involves activities such as reverse engineering (RE) and software visualization. Although several RE tools exist, we found their architecture hard to adapt to the domain and problem specific requirements posed by our current practice in Nokia. In this paper, we present an open architecture which allows easy prototyping of RE data exploration and visualization scenarios for a large range of domain models. We pay special attention to the visual and interactive requirements of the reverse engineering process. We compare our toolkit with other existing reverse engineering visual tools and outline the differences.
Parallel and Out-of-core View-dependent Isocontour Visualization Using Random Data Distribution
(The Eurographics Association, 2002) Zhang, Xiaoyu; Bajaj, Chandrajit; Ramachandran, Vijaya; D. Ebert and P. Brunet and I. Navazo
In this paper we describe a parallel and out-of-core view-dependent isocontour visualization algorithm that efficiently extracts and renders the visible portions of an isosurface from large datasets. The algorithm first creates an occlusion map using ray-casting and nearest neighbors. With the occlusion map constructed, the visible portion of the isosurface is extracted and rendered. All steps are in a single pass with minimal communication overhead. The overall workload is well balanced among parallel processors using random data distribution. Volumetric datasets are statically partitioned onto the local disks of each processor and loaded only when necessary. This out-of-core feature allows it to handle scalably large datasets. We additionally demonstrate significant speedup of the view-dependent isocontour visualization on a commodity off-the-shelf PC cluster.
An Augmented Fast Marching Method for Computing Skeletons and Centerlines
(The Eurographics Association, 2002) Telea, Alexandru; Wijk, Jarke J. van; D. Ebert and P. Brunet and I. Navazo
We present a simple and robust method for computing skeletons for arbitrary planar objects and centerlines for 3D objects. We augment the Fast Marching Method (FMM) widely used in level set applications 11 by computing the paramterized boundary location every pixel came from during the boundary evolution. The resulting parameter field is then thresholded to produce the skeleton branches created by boundary features of a given size. The presented algorithm is straightforward to implement, has low memory costs and short execution times, and is robust with respect to the used threshold and initial shape noisiness. The produced skeletons are very similar to the ones delivered by more complex algorithms. Various 2D and 3D applications are presented.
Viewpoint Entropy: A New Tool for Obtaining Good Views of Molecules
(The Eurographics Association, 2002) Vázquez, Pere-Pau; Feixas, Miquel; Sbert, Mateu; Llobet, Antoni; D. Ebert and P. Brunet and I. Navazo
The computation of good viewpoints is important in several fields: computer graphics, removal of degeneracies in computational geometry, robotics, graph drawing, etc. However, in areas such as computer graphics there is no consensus on what a good viewpoint means and, consequently, each author uses his or her own definition according to the requirements of the application. In this paper we present a formal measure strongly based on Information Theory, viewpoint entropy, that can be applied to certain problems of Computer Graphics such as automatic exploration of objects or scenes and Scene Understanding. We also define a new measure, the orthogonal frustum entropy, in order to fulfill the requirements needed to visualize molecules. We design an algorithm that makes use of graphics hardware to accelerate computation, and whose complexity depends mainly on the number of views we want to analyze. Computation of good views of molecules is useful for molecular scientists, a field which includes practitioners from Crystallography, Chemistry, and Biology.
Visualization of Large Web Access Data Sets
(The Eurographics Association, 2002) Hao, Ming C.; Garg, Pankaj; Dayal, Umeshwar; Machiraju, Vijay; Cotting, Daniel; D. Ebert and P. Brunet and I. Navazo
Many real-world e-service applications require analyzing large volumes of transaction data to extract web access information. This paper describes Web Access Visualization (WAV) a system that visually associates the affinities and relationships of clients and URLs for large volumes of web transaction data. To date, many practical research projects have shown the usefulness of a physics-based mass-spring technique to layout data items with close relationships onto a graph. The WAV system: (1) maps transaction data items (clients, URLs) and their relationships to vertices, edges, and positions on a 3D spherical surface; (2) encapsulates a physics-based engine in a visual data analysis platform; and (3) employs various content sensitive visual techniques - linked multiple views, layered drill-down, and fade in/out - for interactive data analysis. We have applied this system to a web application to analyze web access patterns and trends. The web service quality has been greatly benefited from using the information provided by WAV.
A Novel Approach To Vortex Core Region Detection
(The Eurographics Association, 2002) Jiang, Ming; Machiraju, Raghu; Thompson, David; D. Ebert and P. Brunet and I. Navazo
In this paper we present a simple and efficient vortex core region detection algorithm based on ideas derived from combinatorial topology. These ideas originated from Sperner s lemma, which by itself is of little value to detecting vortex cores. However, we take these ideas from the lemma and apply them in a point-based fashion to detecting vortex core regions. The resulting algorithms for both 2D and 3D are quite simple and very efficient compared to existing ones. We applied our algorithms to both numerically simulated and procedurally generated datasets to illustrate the efficacy of our approach.
AUFLIC: An Accelerated Algorithm For Unsteady Flow Line Integral Convolution
(The Eurographics Association, 2002) Liu, ZhanPing; II, Robert James Moorhead; D. Ebert and P. Brunet and I. Navazo
UFLIC (Unsteady Flow Line Integral Convolution) is an effective texture synthesis technique to visualize unsteady flow with enhanced temporal coherence, but it is time-consuming to generate. This paper presents an accelerated algorithm, called AUFLIC (Accelerated UFLIC), to speed up the UFLIC generation. Our algorithm saves, re-uses, and updates pathlines in the value scattering processes. A flexible seeding strategy is introduced so that a seed particle may be directly extracted from the previous scattering processes to make best use of the saved pathline so as to reduce computationally expensive pathline integration calculations. A dynamic activation-deactivation scheme is employed to maintain the fewest necessary pathlines. Avoiding excessive pathlines achieves acceleration and nearly-constant memory consumption. With very low memory cost, AUFLIC cuts UFLIC generation time nearly in half without any image quality degradation.
Interactive Previewing for Transfer Function Specification in Volume Rendering
(The Eurographics Association, 2002) Botha, Charl P.; Post, Frits H.; D. Ebert and P. Brunet and I. Navazo
This paper presents a new technique for supplying meaningful visual feedback during direct volume rendering transfer function specification. The technique uses meta-data calculated during a pre-processing step to generate interactively an approximate volume rendering that is voxel-registered with a single user-selected slice. Because of the registration, this preview can easily be alpha-blended with a grey-scale image of the data that is being volume rendered. In this way, the user gets real-time visual feedback on her transfer function specification with regards to both the expected composited optical properties and the "fidelity" (how closely the rendering matches the original data) of the resulting rendering.
Useful Properties of Semantic Depth of Field for Better F+C Visualization
(The Eurographics Association, 2002) Kosara, Robert; Miksch, Silvia; Hauser, Helwig; D. Ebert and P. Brunet and I. Navazo
This paper presents the results of a thorough user study that was performed to assess some features and the general usefulness of Semantic Depth of Field (SDOF). Based on these results, concrete hints are given on how SDOF can be used for visualization. SDOF was found to be a very effective means for guiding the viewer s attention and for giving him or her a quick overview of a data set. It can also very quickly be perceived, and therefore provides an efficient visual channel. Semantic Depth of Field is a focus+context (F+C) technique that uses blur to point the user to the most relevant objects. It was inspired by the depth of field (DOF) effect in photography, which serves a very similar purpose.
View-Dependent Multiresolution Splatting of Non-Uniform Data
(The Eurographics Association, 2002) Jang, Justin; Ribarsky, William; Shaw, Christopher D.; Faust, Nickolas; D. Ebert and P. Brunet and I. Navazo
This paper develops an approach for the splat-based visualization of large scale, non-uniform data. A hierarchical structure is generated that permits detailed treatment at the leaf nodes of the non-uniform distribution. A set of levels of detail (LODs) are generated based on the levels of the hierarchy. These yield two metrics, one in terms of the spatial extent of the bounding box containing the splat and one in terms of the variation of the scalar field over this box. The former yields a view-dependent choice of LODs while the latter yields a view-independent LOD based on the field variation. To show the utility of this general approach it is applied to a set of application data for a whole earth environment and some test data. Performance results are given.
Vortex Tracking in Scale-Space
(The Eurographics Association, 2002) Bauer, Dirk; Peikert, Ronald; D. Ebert and P. Brunet and I. Navazo
Scale-space techniques have become popular in computer vision for their capability to access the multiscale information inherently contained in images. We show that the field of flow visualization can benefit from these techniques, too, yielding more coherent features and sorting out numerical artifacts as well as irrelevant large-scale features. We describe an implementation of scale-space computation using finite elements and show that performance is sufficient for computing a scale-space of time-dependent CFD data. Feature tracking, if available, allows to process the information provided by scale-space not just visually but also algorithmically. We present a technique for extending a class of feature extraction schemes by an additional dimension, resulting in an efficient solution of the tracking problem.
Volume Rendering Multivariate Data to Visualize Meteorological Simulations: A Case Study
(The Eurographics Association, 2002) Kniss, Joe; Hansen, Charles; D. Ebert and P. Brunet and I. Navazo
High resolution computational weather models are becoming increasing complex. However, the analysis of these models has not benefited from recent advancements in volume visualization. This case study applies the ideas and techniques from multi-dimensional transfer function based volume rendering to the multivariate weather simulations. The specific goal of identifying frontal zones is addressed. By combining temperature and humidity as a multivariate field, the frontal zones are more readily identified thereby assisting the meteorologists in their analysis tasks.
Speech and Gesture Multimodal Control of a Whole Earth 3D Visualization Environment
(The Eurographics Association, 2002) Krum, David M.; Omoteso, Olugbenga; Ribarsky, William; Starner, Thad; Hodges, Larry F.; D. Ebert and P. Brunet and I. Navazo
A growing body of research shows several advantages to multimodal interfaces including increased expressiveness, flexibility, and user freedom. This paper investigates the design of such an interface that integrates speech and hand gestures. The interface has the additional property of operating relative to the user and can be used while the user is in motion or standing at a distance from the computer display. The paper then describes an implementation of the multimodal interface for a whole Earth 3D visualization which presents navigation interface challenges due to the large magnitude of scale and extended spaces that are available. The characteristics of the multimodal interface are examined, such as speed, recognizability of gestures, ease and accuracy of use, and learnability under likely conditions of use. This implementation shows that such a multimodal interface can be effective in a real environment and sets some parameters for the design and use of such interfaces.
Comparison of Morphological Pyramids for Multiresolution MIP Volume Rendering
(The Eurographics Association, 2002) Roerdink, Jos B.T.M.; D. Ebert and P. Brunet and I. Navazo
We recently proposed a multiresolution representation for maximum intensity projection (MIP) volume rendering based on morphological adjunction pyramids which allow progressive refinement and have the property of perfect reconstruction. In this algorithm the pyramidal analysis and synthesis operators are composed of morphological erosion and dilation, combined with dyadic downsampling for analysis and dyadic upsampling for synthesis. Here we introduce an alternative pyramid scheme in which a morphological opening instead of an erosion is used for pyramidal analysis. As a result, the approximation accuracy when rendering from higher levels of the pyramid is improved.
Shear-Warp Deluxe: The Shear-Warp Algorithm Revisited
(The Eurographics Association, 2002) Sweeney, Jon; Mueller, Klaus; D. Ebert and P. Brunet and I. Navazo
Despite continued advances in volume rendering technology, the Shear-Warp algorithm, although conceived as early as 1994, still remains the world s fastest purely software-based volume rendering algorithm. The impressive speed of near double-digit framerates for moderately sized datasets, however, does come at the price of reduced image quality and memory consumption. In this paper, we present the implementation and impact of certain measures that seek to address these shortcomings. Specifically, we investigate the effects of: (i) post-interpolated classification and shading, (ii) matched volume sampling on zoom, (iii) the interpolation of intermediate slices to reduce inter-slice aliasing, and (iv) the re-use of encoded RLE runs for more than one major viewing direction to preserve memory. We also study a new variation of the shear-warp algorithm that operates on body-centered cubic grids. We find that the reduction of the number of voxels that this grid affords translates into direct savings in rendering times, with minimal degradation in image quality.
A Continuous Skeletonization Method Based on Level Sets
(The Eurographics Association, 2002) Rumpf, Martin; Telea, Alexandru; D. Ebert and P. Brunet and I. Navazo
A robust and efficient method in 2D and 3D for the calculation of skeletons for arbitrary objects is presented. The method is based on the calculation of the distance function with respect to the object boundary. This is combined, in a post processing step, with a new indicator to identify the skeleton, which coincides with the singularity set of the distance map. The indicator is defined as a suitable function of certain local momenta of this distance map and allows a robust and accurate computation of the distance from the skeleton set. This distance is then extended, again via the level set method, onto the whole space. Several applications in 2D and 3D are presented.
Interactive Visualization and Steering of CFD Simulations
(The Eurographics Association, 2002) Kreylos, O.; Tesdall, A. M.; Hamanny, B.; Hunter, J. K.; Joy, K. I.; D. Ebert and P. Brunet and I. Navazo
We describe a system that supports real-time interactive visualization of computational fluid dynamics (CFD) simulations. The system allows a user to place and manipulate visualization primitives, such as isolines and streamlines, during an ongoing simulation process. A user can interactively select and designate regions of the computational mesh for refinement as the simulation progresses, perform remeshing, and see the effects of the refinement on the simulation in real time. The system is being used for the study of two open problems in compressible fluid dynamics. We can interactively explore solutions as they are computed, identify flow field regions containing features of interest, and refine the grid in those regions in order to obtain a better result locally. The ability to visualize "live" data, and to make changes to the computational setup in real time, has helped us to understand the underlying fundamental CFD simulation issues of these problems in shorter times than would otherwise have been possible.
Feature-Preserving Volume Filtering
(The Eurographics Association, 2002) Neumann, László; Csébfalvi, Balázs; Viola, Ivan; Mlejnek, Matej; Gröller, Eduard; D. Ebert and P. Brunet and I. Navazo
In this paper a feature-preserving volume filtering method is presented. The basic idea is to minimize a threecomponent global error function penalizing the density and gradient errors and the curvature of the unknown filtered function. The optimization problem leads to a large linear equation system defined by a sparse coefficient matrix. We will show that such an equation system can be efficiently solved in frequency domain using fast Fourier transformation (FFT). For the sake of clarity, first we illustrate our method on a 2D example which is a dedithering problem. Afterwards the 3D extension is discussed in detail since we propose our method mainly for volume filtering. We will show that the 3D version can be efficiently used for elimination of the typical staircase artifacts of direct volume rendering without losing fine details. Unlike local filtering techniques, our novel approach ensures a global smoothing effect. Previous global 3D methods are restricted to binary volumes or segmented iso-surfaces and they are based on area minimization of one single reconstructed surface. In contrast, our method is a general volume-filtering technique, implicitly smoothing all the iso-surfaces at the same time. Although the strength of the presented algorithm is demonstrated on a specific 2D and a specific 3D application, it is considered as a general mathematical tool for processing images and volumes.

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