DevLan/vispubs huggingface dataset:
Fast extraction of adaptive multiresolution meshes with guaranteed properties from volumetric data
Authors: Marcel Gavriliu, Joel Carranza, David E. Breen, Alan H. Barr
Published at Vis, 2001

We present a new algorithm for extracting adaptive multiresolution triangle meshes from volume datasets. The algorithm guarantees that the topological genus of the generated mesh is the same as the genus of the surface embedded in the volume dataset at all levels of detail. In addition to this "hard constraint" on the genus of the mesh, the user can choose to specify some number of soft geometric constraints, such as triangle aspect ratio, minimum or maximum total number of vertices, minimum and/or maximum triangle edge lengths, maximum magnitude of various error metrics per triangle or vertex, including maximum curvature (area) error, maximum distance to the surface, and others. The mesh extraction process is fully automatic and does not require manual adjusting of parameters to produce the desired results as long as the user does not specify incompatible constraints. The algorithm robustly handles special topological cases, such as trimmed surfaces (intersections of the surface with the volume boundary), and manifolds with multiple disconnected components (several closed surfaces embedded in the same volume dataset). The meshes may self-intersect at coarse resolutions. However, the self-intersections are corrected automatically as the resolution of the meshes increase. We show several examples of meshes extracted from complex volume datasets.
Fitting Subdivision Surfaces
Authors: Nathan Litke, Adi Levin, Peter Schröder
Published at Vis, 2001

We introduce a new algorithm for fitting a Catmull-Clark subdivision surface to a given shape within a prescribed tolerance, based on the method of quasi-interpolation. The fitting algorithm is fast, local and scales well since it does not require the solution of linear systems. Its convergence rate is optimal for regular meshes and our experiments show that it behaves very well for irregular meshes. We demonstrate the power and versatility of our method with examples from interactive modeling, surface fitting, and scientific visualization.
Graphical strategies to convey functional relationships in the human brain: a case study
Authors: Tomihisa Welsh, Klaus Mueller 0001, Wei Zhu 0008, Nora D. Volkow, Jeffrey Meade
Published at Vis, 2001

Brain imaging methods used in experimental brain research such as Positron Emission Tomography (PET) and Functional Magnetic Resonance (fMRI) require the analysis of large amounts of data. Exploratory statistical methods can be used to generate new hypotheses and to provide a reliable measure of a given effect. Typically, researchers report their findings by listing those regions which show significant statistical activity in a group of subjects under some experimental condition or task. A number of methods create statistical parametric maps (SPMs) of the brain on a voxel-basis. In our approach statistics are computed not on individual voxels but on predefined anatomical regions-of-interest (ROIs). A correlation coefficient is used to quantify similarity in response for various regions during an experimental setting. Since the functional inter-relationships can become rather complex and spatially widespread, they are best understood in the context of the underlying 3-D brain anatomy. However despite the power of the 3-D model, the relative location of ROIs in 3-D can be obscured due the inherent problem of presenting 3-D spatial information on a 2-D screen. In order to address this problem, we have explored a number of visualization techniques to aid the brain researcher in exploring the spatial relationships of brain activity. In this paper we present a novel 3-D interface that allows the interactive exploration of correlation datasets.
Hardware-software-balanced resampling for the interactive visualization of unstructured grids
Authors: Manfred Weiler, Thomas Ertl
Published at Vis, 2001

In this paper we address the problem of interactively resampling unstructured grids. Three algorithms are presented. They all allow adaptive resampling of an unstructured grid on a multiresolution hierarchy of arbitrarily sized cartesian grids according to a varying element size. Two of the algorithms presented take advantage of hardware accelerated polygon rendering and 2D texture mapping. In exploiting new features of modem PC graphics adapters, the first algorithm tries to significantly minimize the number of polygons to be rendered. Reducing rasterization requirements is the main goal of the second algorithm, which distributes the computational workload differently between the main processor and the graphics chip. By comparing them to a new pure software approach, an optimal software-hardware balance is studied. We end up with a hybrid approach which greatly improves the performance of hardware assisted resampling by involving the main processor to a higher degree and thus enabling resampling at nearly interactive rates.
Hybrid simplification: combining multi-resolution polygon and point rendering
Authors: Jonathan D. Cohen 0001, Daniel G. Aliaga, Weiqiand Zhang
Published at Vis, 2001

Multi-resolution hierarchies of polygons and more recently of points are familiar and useful tools for achieving interactive rendering rates. We present an algorithm for tightly integrating the two into a single hierarchical data structure. The trade-off between rendering portions of a model with points or with polygons is made automatically. Our approach to this problem is to apply a bottom-up simplification process involving not only polygon simplification operations, but point replacement and point simplification operations as well. Given one or more surface meshes, our algorithm produces a hybrid hierarchy comprising both polygon and point primitives. This hierarchy may be optimized according to the relative performance characteristics of these primitive types on the intended rendering platform. We also provide a range of aggressiveness for performing point replacement operations. The most conservative approach produces a hierarchy that is better than a purely polygonal hierarchy in some places, and roughly equal in others. A less conservative approach can trade reduced complexity at the far viewing ranges for some increased complexity at the near viewing ranges. We demonstrate our approach on a number of input models, achieving primitive counts that are 1.3 to 4.7 times smaller than those of triangle-only simplification.
Integrating occlusion culling with view-dependent rendering
Authors: Jihad El-Sana, Neta Sokolovsky, Cláudio T. Silva
Published at Vis, 2001

We present an approach that integrates occlusion culling within the view-dependent rendering framework. View-dependent rendering provides the ability to change level of detail over the surface seamlessly and smoothly in real-time. The exclusive use of view-parameters to perform level-of-detail selection causes even occluded regions to be rendered in high level of detail. To overcome this serious drawback we have integrated occlusion culling into the level selection mechanism. Because computing exact visibility is expensive and it is currently not possible to perform this computation in real time, we use a visibility estimation technique instead. Our approach reduces dramatically the resolution at occluded regions.
Interactive volume rendering using multi-dimensional transfer functions and direct manipulation widgets
Authors: Joe Michael Kniss, Gordon L. Kindlmann, Charles D. Hansen
Published at Vis, 2001

Most direct volume renderings produced today employ one-dimensional transfer functions, which assign color and opacity to the volume based solely on the single scalar quantity which comprises the dataset. Though they have not received widespread attention, multi-dimensional transfer functions are a very effective way to extract specific material boundaries and convey subtle surface properties. However, identifying good transfer functions is difficult enough in one dimension, let alone two or three dimensions. This paper demonstrates an important class of three-dimensional transfer functions for scalar data (based on data value, gradient magnitude, and a second directional derivative), and describes a set of direct manipulation widgets which make specifying such transfer functions intuitive and convenient. We also describe how to use modem graphics hardware to interactively render with multi-dimensional transfer functions. The transfer functions, widgets, and hardware combine to form a powerful system for interactive volume exploration.
Lagrangian-Eulerian Advection for Unsteady Flow Visualization
Authors: Bruno Jobard, Gordon Erlebacher, M. Yousuff Hussaini
Published at Vis, 2001

In this paper, we propose a new technique to visualize dense representations of time-dependent vector fields based on a Lagrangian-Eulerian Advection (LEA) scheme. The algorithm produces animations with high spatio-temporal correlation at interactive rates. With this technique, every still frame depicts the instantaneous structure of the flow, whereas an animated sequence of frames reveals the motion a dense collection of particles would take when released into the flow. The simplicity of both the resulting data structures and the implementation suggest that LEA could become a useful component of any scientific visualization toolkit concerned with the display of unsteady flows.
Multiresolution feature extraction for unstructured meshes
Authors: Andreas Hubeli, Markus H. Gross
Published at Vis, 2001

We present a framework to extract mesh features from unstructured two-manifold surfaces. Our method computes a collection of piecewise linear curves describing the salient features of surfaces, such as edges and ridge lines. We extend these basic techniques to a multiresolution setting which improves the quality of the results and accelerates the extraction process. The extraction process is semi-automatic, that is, the user is required to input a few control parameters and to select the operators to be applied to the input surface. Our mesh feature extraction algorithm can be used as a preprocessor for a variety of applications in geometric modeling including mesh fairing, subdivision and simplification.
Nonlinear virtual colon unfolding
Authors: Anna Vilanova, Rainer Wegenkittl, Andreas König 0002, M. Eduard Gröller
Published at Vis, 2001

The majority of virtual endoscopy techniques tries to simulate a real endoscopy. A real endoscopy does not always give the optimal information due to the physical limitations it is subject to. In this paper, we deal with the unfolding of the surface of the colon as a possible visualization technique for diagnosis and polyp detection. A new two-step technique is presented which deals with the problems of double appearance of polyps and nonuniform sampling that other colon unfolding techniques suffer from. In the first step, a distance map from a central path induces nonlinear rays for unambiguous parameterization of the surface. The second step compensates for locally varying distortions of the unfolded surface. A technique similar to magnification fields in information visualization is hereby applied. The technique produces a single view of a complete, virtually dissected colon.
Nonmanifold subdivision
Authors: Lexing Ying, Denis Zorin
Published at Vis, 2001

Commonly-used subdivision schemes require manifold control meshes and produce manifold surfaces. However, it is often necessary to model nonmanifold surfaces, such as several surface patches meeting at a common boundary. In this paper, we describe a subdivision algorithm that makes it possible to model nonmanifold surfaces. Any triangle mesh, subject only to the restriction that no two vertices of any triangle coincide, can serve as an input to the algorithm. Resulting surfaces consist of collections of manifold patches joined along nonmanifold curves and vertices. If desired, constraints may be imposed on the tangent planes of manifold patches sharing a curve or a vertex. The algorithm is an extension of a well-known Loop subdivision scheme, and uses techniques developed for piecewise smooth surfaces.
Normal bounds for subdivision-surface interference detection
Authors: Eitan Grinspun, Peter Schröder
Published at Vis, 2001

Subdivision surfaces are an attractive representation when modeling arbitrary-topology free-form surfaces and show great promise for applications in engineering design and computer animation. Interference detection is a critical tool in many of these applications. In this paper, we derive normal bounds for subdivision surfaces and use these to develop an efficient algorithm for (self-) interference detection.
Optimal regular volume sampling
Authors: Thomas Theußl, Torsten Möller, M. Eduard Gröller
Published at Vis, 2001

The classification of volumetric data sets as well as their rendering algorithms are typically based on the representation of the underlying grid. Grid structures based on a Cartesian lattice are the de-facto standard for regular representations of volumetric data. In this paper we introduce a more general concept of regular grids for the representation of volumetric data. We demonstrate that a specific type of regular lattice-the so-called body-centered cubic-is able to represent the same data set as a Cartesian grid to the same accuracy but with 29.3% fewer samples. This speeds up traditional volume rendering algorithms by the same ratio, which we demonstrate by adopting a splatting implementation for these new lattices. We investigate different filtering methods required for computing the normals on this lattice. The lattice representation results also in lossless compression ratios that are better than previously reported. Although other regular grid structures achieve the same sample efficiency, the body-centered cubic is particularly easy to use. The only assumption necessary is that the underlying volume is isotropic and band-limited-an assumption that is valid for most practical data sets.
PingTV: A Case Study in Visual Network Monitoring
Authors: Alexander Gubin, William Yurcik, Larry Brumbaugh
Published at Vis, 2001

PingTV generates a logical map of a network that is used as an overlay on a physical geographical image of the location from the user perspective (buildings, floors within buildings, etc.). PingTV is used at Illinois State University as a visualization tool to communicate real-time network conditions to the university community via a dedicated channel on the campus cable TV system. Colored symbols allow students and staff to discern high-congestion "rush hours" and understand why their specific Internet connectivity is "broken" from the wide range of potential causes. Lessons learned include the use of color to visually convey confidence intervals using color shading and the visualization of cyclical network traffic patterns. Our implementation is general and flexible with potential for application for other domains.
PixelFlex: a reconfigurable multi-projector display system
Authors: Ruigang Yang, David Gotz, Justin Hensley, Herman Towles, Michael S. Brown
Published at Vis, 2001

This paper presents PixelFlex - a spatially reconfigurable multi-projector display system. The PixelFlex system is composed of ceiling-mounted projectors, each with computer-controlled pan, tilt, zoom and focus; and a camera for closed-loop calibration. Working collectively, these controllable projectors function as a single logical display capable of being easily modified into a variety of spatial formats of differing pixel density, size and shape. New layouts are automatically calibrated within minutes to generate the accurate warping and blending functions needed to produce seamless imagery across planar display surfaces, thus giving the user the flexibility to quickly create, save and restore multiple screen configurations. Overall, PixelFlex provides a new level of automatic reconfigurability and usage, departing from the static, one-size-fits-all design of traditional large-format displays. As a front-projection system, PixelFlex can be installed in most environments with space constraints and requires little or no post-installation mechanical maintenance because of the closed-loop calibration.
Point set surfaces
Authors: Marc Alexa, Johannes Behr, Daniel Cohen-Or, Shachar Fleishman, David Levin, Cláudio T. Silva
Published at Vis, 2001

We advocate the use of point sets to represent shapes. We provide a definition of a smooth manifold surface from a set of points close to the original surface. The definition is based on local maps from differential geometry, which are approximated by the method of moving least squares (MLS). We present tools to increase or decrease the density of the points, thus, allowing an adjustment of the spacing among the points to control the fidelity of the representation. To display the point set surface, we introduce a novel point rendering technique. The idea is to evaluate the local maps according to the image resolution. This results in high quality shading effects and smooth silhouettes at interactive frame rates.
POP: A Hybrid Point and Polygon Rendering System for Large Data
Authors: Baoquan Chen, Minh Xuan Nguye
Published at Vis, 2001

We introduce a simple but effective extension to the existing pure point rendering systems. Rather than using only points, we use both points and polygons to represent and render large mesh models. We start from triangles as leaf nodes and build up a hierarchical tree structure with intermediate nodes as points. During the rendering, the system determines whether to use a point (of a certain intermediate level node) or a triangle (of a leaf node) for display depending on the screen contribution of each node. While points are used to speedup the rendering of distant objects, triangles are used to ensure the quality of close objects. Our method can accelerate the rendering of large models, compromising little in image quality.
Quantitative comparative evaluation of 2D vector field visualization methods
Authors: David H. Laidlaw, Robert M. Kirby, J. Scott Davidson, Timothy S. Miller, Marco da Silva, William H. Warren, Michael J. Tarr
Published at Vis, 2001

Presents results from a user study that compared six visualization methods for 2D vector data. Two methods used different distributions of short arrows, two used different distributions of integral curves, one used wedges located to suggest flow lines, and the final one was line-integral convolution (LIC). We defined three simple but representative tasks for users to perform using visualizations from each method: (1) locating all critical points in an image, (2) identifying critical point types, and (3) advecting a particle. The results show different strengths and weaknesses for each method. We found that users performed better with methods that: (1) showed the sign of vectors within the vector field, (2) visually represented integral curves, and (3) visually represented the locations of critical points. These results provide quantitative support for some of the anecdotal evidence concerning visualization methods. The tasks and testing framework also provide a basis for comparing other visualization methods, for creating more effective methods and for defining additional tasks to further understand tradeoffs among methods. They may also be useful for evaluating 2D vectors on 2D surfaces embedded in 3D and for defining analogous tasks for 3D visualization methods.
Real-time decompression and visualization of animated volume data
Authors: Stefan Guthe, Wolfgang Straßer
Published at Vis, 2001

Interactive exploration of animated volume data is required by many application, but the huge amount of computational time and storage space needed for rendering does not yet allow the visualization of animated volumes. In this paper, we introduce an algorithm running at interactive frame rates using 3D wavelet transforms that allows for any wavelet, motion compensation techniques and various encoding schemes of the resulting wavelet coefficients to be used. We analyze different families and orders of wavelets for compression ratio and the introduced error. We use a quantization that has been optimized for the visual impression of the reconstructed volume, independent of the viewing algorithm. This enables us to achieve very high compression ratios while still being able to reconstruct the volume with as few visual artifacts as possible. A further improvement of the compression ratio has been achieved by applying a motion compensation scheme to exploit temporal coherency. Using these schemes, we are able to decompress each volume of our animation at interactive frame rates, while visualizing these decompressed volumes on a single PC. We also present a number of improved visualization algorithms for high-quality display using OpenGL hardware running at interactive frame rates on a standard PC.
RTVR-a flexible Java library for interactive volume rendering
Authors: Lukas Mroz, Helwig Hauser
Published at Vis, 2001

This paper presents several distinguishing design features of RTVR-a Java-based library for real-time volume rendering. We describe, how the careful design of data structures, which in our case are based on voxel enumeration, and an intelligent use of lookup tables enable interactive volume rendering even on low-end PC hardware. By assigning voxels to distinct objects within the volume and by using an individual setup and combination of look-up tables for each object, object-aware rendering is performed: different transfer functions, shading models, and also compositing modes can be mixed within a single scene to depict each object in the most appropriate way, while still providing rendering results in real-time. While providing frame rates similar to volume visualization using 3D consumer hardware, the approach utilized by RTVR offers much more flexibility and extensibility due to its pure software nature. Furthermore, due to the memory-efficiency of the data representation and the implementation in Java, RTVR can be used to provide volume viewing facilities over low-bandwidth networks, with almost full control over rendering and visualization mapping parameters (clipping, shading, compositing, transfer function) for the user. This paper also addresses specific problems which arise by the use of Java for interactive visualization.
Salient iso-surface detection with model-independent statistical signatures
Authors: Shivaraj Tenginakai, Jinho Lee, Raghu Machiraju
Published at Vis, 2001

Volume graphics has not been accepted for widespread use. One of the inhibiting reasons is the lack of general methods for data-analysis and simple interfaces for data exploration. An error-and-trial iterative procedure is often used to select a desirable transfer function or mine the dataset for salient iso-values. New semi-automatic methods that are also data-centric have shown much promise. However, general and robust methods are still needed for data-exploration and analysis. In this paper, we propose general model-independent statistical methods based on central moments of data. Using these techniques we show how salient iso-surfaces at material boundaries can be determined. We provide examples from the medical and computational domain to demonstrate the effectiveness of our methods.