IEEE VIS Publication Dataset

Visualization of computational oceanography is traditionally a post-processing step. This batch orientation is clumsy if one wants to observe the effect of a wide range of parameters on the solution. This paper describes the conversion of an ocean circulation model from this traditional design to an interactive program in which the computed solution is viewed in real-time over a wide-area network and the user is given the ability to change the model parameters and immediately observe the impact this has on the solution.

We present efficient sequential and parallel algorithms for isosurface extraction. Based on the Span Space data representation, new data subdivision and searching methods are described. We also present a parallel implementation with an emphasis on load balancing. The performance of our sequential algorithm to locate the cell elements intersected by isosurfaces is faster than the Kd tree searching method originally used for the Span Space algorithm. The parallel algorithm can achieve high load balancing for massively parallel machines with distributed memory architectures.

Integrated presentation of data with uncertainty is a worthy goal in scientific visualization. It allows researchers to make informed decisions based on imperfect data. It also allows users to visually compare and contrast different algorithms for performing the same task or different models for representing the same physical phenomenon. We present LISTEN-a data sonification system that has been incorporated into two visualization systems: a system for visualizing geometric uncertainty of surface interpolants; and a system for visualizing uncertainty in fluid flow. LISTEN is written in C++ for the SGI platform. It works with the SGI internal audio chip or a MIDI device or both. LISTEN is an object-oriented system that is modular, flexible, adaptable, portable, interactive and extensible. We demonstrate that sonification is very effective as an additional tool in visualizing geometric and fluid flow uncertainty.

In many cases the surfaces of geometric models consist of a large number of triangles. Several algorithms were developed to reduce the number of triangles required to approximate such objects. Algorithms that measure the deviation between the approximated object and the original object are only available for special cases. We use the Hausdorff distance between the original and the simplified mesh as a geometrically meaningful error value which can be applied to arbitrary triangle meshes. We present a new algorithm to reduce the number of triangles of a mesh without exceeding a user defined Hausdorff distance between the original and simplified mesh. As this distance is parameterization independent, its use as error measure is superior to the use of the L ∞-Norm between parameterized surfaces. Furthermore the Hausdorff distance is always less than the distance induced by the L ∞-Norm. This results in higher reduction rates. Excellent results were achieved by the new decimation algorithm for triangle meshes that has been used in different application areas such as volume rendering, terrain modeling and the approximations of parameterized surfaces. The key advantages of the new algorithm are: it guarantees a user defined position dependent approximation error; it allows one to generate a hierarchical geometric representation in a canonical way; it automatically preserves sharp edges.

We present a way to visualize a flow field using Line Integral Convolution (LIC) with a multi frequency noise texture. A broad range of feature sizes can enhance a user's perception of the magnitudes and direction of the flow. In addition, the multiple scales of feature size help a user clarify the motion of the flow in an animation.

Brushing is a data visualization technique that identifies and highlights data subsets. We introduce a form of brushing in which the brushed data is usually displayed at a different resolution than the non brushed data. The paper presents the rationale behind the multiresolution support of multivariate data visualization and describes the construction of multiresolution brushing using wavelet approximations. The idea is implemented in an enhanced version of XmdvTool. Real scientific data is used for demonstration and practical applications are suggested.

The marching cubes (MC) algorithm is a method for generating isosurfaces. It also generates an excessively large number of triangles to represent an isosurface; this increases the rendering time. This paper presents a decimation method to reduce the number of triangles generated. Decimation is carried out before creating a large number of triangles. Four major steps comprise the algorithm: surface tracking, merging, crack patching and triangulation. Surface tracking is an enhanced implementation of the MC algorithm. Starting from a seed point, the surface tracker visits only those cells likely to compose part of the desired isosurface. The cells making up the extracted surface are stored in an octree that is further processed. A bottom-up approach is taken in merging the cells containing a relatively flat approximating surface. The finer surface details are maintained. Cells are merged as long as the error due to such an operation is within a user-specified error parameter, or a cell acquires more than one connected surface component in it. A crack patching method is described that forces edges of smaller cells to lie along those of the larger neighboring cells. The overall saving in the number of triangles depends both on the specified error value and the nature of the data. Use of the hierarchical octree data structure also presents the potential of incremental representation of surfaces. We can generate a highly smoothed surface representation which can be progressively refined as the user-specified error value is decreased.

Many scientific and medical visualization techniques produce irregular surfaces whose shape and structure need to be understood. Examples include tissue and tumor boundaries in medical imaging, molecular surfaces and force thresholds in chemical and pharmaceutical applications, and isosurfaces in a wide range of 3D domains. The 3D shape of such surfaces can be particularly difficult to interpret because of the unfamiliar, irregular shapes, the potential concavities and bulges, and the lack of parallel lines and right angles to provide perspective depth cues. Attempts to display multiple irregular surfaces by making some or all of them transparent further complicates the problem. Texture can provide valuable cues to aid in the interpretation of irregular surfaces. Opacity-modulating textures offer a mechanism for the display of multiple surfaces without the extreme loss of clarity of multiple transparent surfaces. This paper presents a method for creating simple repeating textures and mapping them onto irregular surfaces.

Almost all scientific visualization involving surfaces is currently done via triangles. The speed at which such triangulated surfaces can be displayed is crucial to interactive visualization and is bounded by the rate at which triangulated data can be sent to the graphics subsystem for rendering. Partitioning polygonal models into triangle strips can significantly reduce rendering times over transmitting each triangle individually. We present new and efficient algorithms for constructing triangle strips from partially triangulated models, and experimental results showing these strips are on average 15% better than those from previous codes. Further, we study the impact of larger buffer sizes and various queuing disciplines on the effectiveness of triangle strips.

Whilst there has been considerable effort in constructing force feedback devices for use in virtual environments, and in the use of touch as a prosthesis for the blind, there has been little work on the use of touch in the visualisation or more properly, perceptualisation of data. Touch potentially offers an additional dimension of perception where visualisation is limited by screen size, resolution, and visual overload. We describe some tactile mice and experiments in using tactile mice for a variety of perceptualisation tasks.

Direct Volume Rendering (DVR) allows the holistic visualization of huge volumetric data sets in a single image. Computational fluid dynamics data is in principle well suited for DVR. But efficient mappings of the directional information of vector fields are still to be found. We investigate how the raycasting technique can be used to directly render vector fields. Our approach is based on the perception that other flow visualization techniques use visualization objects that are locally tangential to the vector field together with directed light sources. From this, we developed the idea to shade streamlines at sampling points when raycasting a vector field. We extended this approach further to more abstract mappings where pseudo color is used. Combining opacity mapping, pseudo color mapping, and streamline shading we can express flow speed and flow direction together in one single image.

We present a method for producing real-time volume visualizations of continuously captured, arbitrarily-oriented 2D arrays (slices) of data. Our system constructs a 3D representation on-the-fly from incoming 2D ultrasound slices by modeling and rendering the slices as planar polygons with translucent surface textures. We use binary space partition (BSP) tree data structures to provide non-intersecting, visibility-ordered primitives for accurate opacity accumulation images. New in our system is a method of using parallel, time-shifted BSP trees to efficiently manage the continuously captured ultrasound data and to decrease the variability in image generation time between output frames. This technique is employed in a functioning real-time augmented reality system that a physician has used to examine human patients prior to breast biopsy procedures. We expect the technique can be used for real-time visualization of any 2D data being collected from a tracked sensor moving along an arbitrary path.

Real time rendering of iso contour surfaces is problematic for large complex data sets. An algorithm is presented that allows very rapid representation of an interval set surrounding an iso contour surface. The algorithm draws upon three main ideas. A fast indexing scheme is used to select only those data points near the contour surface. Hardware assisted splatting is then employed on these data points to produce a volume rendering of the interval set. Finally, by shifting a small window through the indexing scheme or data space, animated volumes are produced showing the changing contour values. In addition to allowing fast selection and rendering of the data, the indexing scheme allows a much compressed representation of the data by eliminating "noise" data points.

The definition of consonance as the ability to resolve a sound into the pitch categories is introduced. For a vector space of chords a norm is used to evaluate the consonance linearly in dependence of the instrument used. It is shown that in the corresponding Hilbert space the chords which usually appear together in a conventional musical piece are recognized in terms of "closeness".

The representation of a scene at different levels of detail is necessary to achieve real-time rendering. In aerial views, only the part of the scene that is close to the viewing point needs to be displayed with a high level of detail, while more distant parts can be displayed with a low level of detail. However, when a sequence of images is generated and displayed in real-time, the transition between different levels of detail causes noticeable temporal aliasing. In this paper, we propose a method, based on object blending, that visually softens the transition between two levels of Delaunay triangulation. We present an algorithm that establishes, in an off-line process, a correspondence between two given polygonal objects. The correspondence enables on-line blending between two representations of an object, so that one representation (level of detail) progressively evolves into the other.

Existing volume visualization techniques are typically applied to a three-dimensional grid. This presents some challenging problems in the visualization of environmental data. This data often consists of unevenly distributed samples. Typically a two-step approach is used to visualize environmental data. First the unevenly distributed sample data are modeled onto a uniform 3-D grid. This grid model is subsequently rendered using conventional grid-based visualization techniques. This paper discusses some of the limitations of this approach and highlights areas where further research is needed to improve the accuracy of visualization for environmental applications.

The Visualization Toolkit (vtk) is afreely available C++ class library for 30 graphics and visualization. In this paper we describe core characteristics of the toolkit. This includes a description of object-oriented models for graphics and visualization; methods for synchronizing system execution: a summary of data representation schemes; the role of C+ +; issues in portability across PC and Unix systems; and how we automatically wrap the C+ + class library with interpreted languages such as Java and Tel. We also demonstrate the capabilities of the system for scalar, vector, tensor, and other visualization techniques.