IEEE VIS Publication Dataset

We propose a technique for visualizing steady flow. Using this technique, we first convert the vector field data into a scalar level-set representation. We then analyze the dynamic behavior and subsequent distortion of level-sets and interactively monitor the evolving structures by means of texture-based surface rendering. Next, we combine geometrical and topological considerations to derive a multiscale representation and to implement a method for the automatic placement of a sparse set of graphical primitives depicting homogeneous streams in the fields. Using the resulting algorithms, we have built a visualization system that enables us to effectively display the flow direction and its dynamics even for dense 3D fields.

As the size and complexity of data sets continues to increase, the development of user interfaces and interaction techniques that expedite the process of exploring that data must receive new attention. Regardless of the speed of rendering, it is important to coherently organize the visual process of exploration: this information both grants insights about the data to a user and can be used by collaborators to understand the results. To fulfil these needs, we present a spreadsheet-like interface to data exploration. The interface displays a 2-dimensional window into visualization parameter space which users manipulate as they search for desired results. Through tabular organization and a clear correspondence between parameters and results, the interface eases the discovery, comparison and analysis of the underlying data. Users can utilize operators and the integrated interpreter to further explore and automate the visualization process; using a method introduced in this paper, these operations can be applied to cells in different stacks of the interface. Via illustrations using a variety of data sets, we demonstrate the efficacy of this novel interface.

Topology analysis of plane, turbulent vector fields results in visual clutter caused by critical points indicating vortices of finer and finer scales. A simplification can be achieved by merging critical points within a prescribed radius into higher order critical points. After building clusters containing the singularities to merge, the method generates a piecewise linear representation of the vector field in each cluster containing only one (higher order) singularity. Any visualization method can be applied to the result after this process. Using different maximal distances for the critical points to be merged results in a hierarchy of simplified vector fields that can be used for analysis on different scales.

We present a new visibility determination algorithm for interactive virtual endoscopy. The algorithm uses a modified version of template-based ray casting to extract a view dependent set of potentially visible voxels from volume data. The voxels are triangulated by Marching Cubes and the triangles are rendered onto the display by a graphics accelerator. Early ray termination and space leaping are used to accelerate the ray casting step and a quadtree subdivision algorithm is used to reduce the number of cast rays. Compared to other recently proposed rendering algorithms for virtual endoscopy, our rendering algorithm does not require a long preprocessing step or a high-end graphics workstation, but achieves interactive frame rates on a standard PC equipped with a low-cost graphics accelerator.

Large area tiled displays are gaining popularity for use in collaborative immersive virtual environments and scientific visualization. While recent work has addressed the issues of geometric registration, rendering architectures, and human interfaces, there has been relatively little work on photometric calibration in general, and photometric non-uniformity in particular. For example, as a result of differences in the photometric characteristics of projectors, the color and intensity of a large area display varies from place to place. Further, the imagery typically appears brighter at the regions of overlap between adjacent projectors. We analyze and classify the causes of photometric non-uniformity in a tiled display. We then propose a methodology for determining corrections designed to achieve uniformity, that can correct for the photometric variations across a tiled projector display in real time using per channel color look-up-tables (LUT).

We describe a toolkit for the design and visualization of flexible artificial heart valves. The toolkit consists of interlinked modules with a visual programming interface. The user of the toolkit can set the initial geometry and material properties of the valve leaflet, solve for the flexing of the leaflet and the flow of blood around it, and display the results using the visualization capabilities of the toolkit. The interactive nature of our environment is highlighted by the fact that changes in leaflet properties are immediately reflected in the flow field and response of the leaflet. Hence the user may, in a single session, investigate a broad range of designs, each one of which provides important information about the blood flow and motion of the valve during the cardiac cycle.

A new multiscale method in surface processing is presented which combines the image processing methodology based on nonlinear diffusion equations and the theory of geometric evolution problems. Its aim is to smooth discretized surfaces while simultaneously enhancing geometric features such as edges and corners. This is obtained by an anisotropic curvature evolution, where time is the multiscale parameter. Here, the diffusion tensor depends on the shape operator of the evolving surface. A spatial finite element discretization on arbitrary unstructured triangular meshes and a semi-implicit finite difference discretization in time are the building blocks of the easy to code algorithm presented. The systems of linear equations in each timestep are solved by appropriate, preconditioned iterative solvers. Different applications underline the efficiency and flexibility of the presented type of surface processing tool.

A scalable, high-resolution display may be constructed by tiling many projected images over a single display surface. One fundamental challenge for such a display is to avoid visible seams due to misalignment among the projectors. Traditional methods for avoiding seams involve sophisticated mechanical devices and expensive CRT projectors, coupled with extensive human effort for fine-tuning the projectors. The paper describes an automatic alignment method that relies on an inexpensive, uncalibrated camera to measure the relative mismatches between neighboring projectors, and then correct the projected imagery to avoid seams without significant human effort.

This is basic research for assigning color values to voxels of multichannel MRI volume data. The MRI volume data sets obtained under different scanning conditions are transformed into their components by independent component analysis (ICA), which enhances the physical characteristics of the tissue. The transfer functions for generating color values from independent components are obtained using a radial basis function network, a kind of neural net, by training the network with sample data chosen from the Visible Female data set. The resultant color volume data sets correspond well with the full-color cross-sections of the Visible Human data sets.

We present a segmentation approach to scientific visualization that combines the definition of higher-level data, the efficient extraction of meaningful derived feature-like data from defined properties, and the effective visual representation of the extracted data. Our frame- work is aimed at multi-valued time-varying data sets, where, for example, grid vertices might have a multitude of associated scalar, vector and tensor quantities. This “segmentation” approach to massive data set exploration allows the user to focus upon regions, and interactively explore these regions efficiently. The challenge is to generate this segmented data from existing multi-valued data sets, store this data in an efficient scheme, generate the boundaries of each region, and display these boundaries to the user. We present an integrated scheme that allows a common representation for seg- mentation, allows it to be applied to a number of data types, and allows derived representations to be calculated. We illustrate this framework with examples from scalar-and vector-field visualization.

Applications of visualization techniques that facilitate comparison of simulation and field datasets of seafloor hydrothermal plumes are demonstrated in order to explore and confirm theories of plume behavior. In comparing these datasets, there is no one-to-one correspondence. We show the comparison by performing quantitative capturing of large scale observable features. The comparisons are needed not only to improve the relevance of the simulations to the field observations, but also to enable real time adjustment of shipboard data collection systems. Our approach for comparing simulation and field datasets is to use skeletonization and centerline representation. Features representing plumes are skeletonized. Skeleton points are used to construct a centerline and to quantify plume properties on planes normal to the centerline. These skeleton points are further used to construct an idealized cone representing a plume isosurface. The difference between the plume feature and the cone is identified as protrusions of turbulent eddies. Comparison of the simulation and field data sets through these abstractions illustrates how these abstractions characterize a plume.

We present CEASAR, a centerline extraction algorithm that delivers smooth, accurate and robust results. Centerlines are needed for accurate measurements of length along winding tubular structures. Centerlines are also required in automatic virtual navigation through human organs, such as the colon or the aorta, as they are used to control movement and orientation of the virtual camera. We introduce a concise but general definition of a centerline, and provide an algorithm that finds the centerline accurately and rapidly. Our algorithm is provably correct for general geometries. Our solution is fully automatic, which frees the user from having to engage in data preprocessing. For a number of test datasets, we show the smooth and accurate centerlines computed by our CEASAR algorithm on a single 194 MHz MIPS R10000 CPU within five minutes.

For a comprehensive understanding of tomographic image data in medicine, interactive and high-quality direct volume rendering is an essential prerequisite. This is provided by visualization using 3D texture mapping which is still limited to high-end graphics hardware. In order to make it available in a clinical environment, we present a system which uniquely combines local desktop computers and remote high-end graphics hardware. In this context, we exploit the standard visualization capabilities to a maximum which are available in the clinical environment. For 3D representations of high resolution and quality we access the remote specialized hardware. Various tools for 2D and 3D visualization are provided which meet the requirements of a medical diagnosis. This is demonstrated with examples from the field of neuroradiology which show the value of our strategy in practice.

We present a new algorithm for material boundary interface reconstruction from data sets containing volume fractions. We transform the reconstruction problem to a problem that analyzes the dual data set, where each vertex in the dual mesh has an associated barycentric coordinate tuple that represents the fraction of each material present. After constructing the dual tetrahedral mesh from the original mesh, we construct material boundaries by mapping a tetrahedron into barycentric space and calculating the intersections with Voronoi cells in barycentric space. These intersections are mapped back to the original physical space and triangulated to form the boundary surface approximation. This algorithm can be applied to any grid structure and can treat any number of materials per element/vertex.

Richly expressive information visualizations are difficult to design and rarely found. Few software tools can generate multidimensional visualizations at all, let alone incorporate artistic detail. Althrough, it is a great efficiency to reuse these visualizations with new data, the associated artistic detail is rarely reusable. The Relational Visualization Notation is a new technique and toolkit for specifying highly expressive graphical representations of data without traditional programming. We seek to discover the accessible power of this notation—both its graphical expressiveness and its ease of re-use. Towards this end we have used the system to reconstruct Minard’s visualization of Napoleon’s Russian campaign of 1812. The resulting image is strikingly similar to the original, and the design is straightforward to construct. Furthermore, the design permitted by the notation can be directly reused to visualize Hitler’s WWII defeat before Moscow. This experience leads us to believe that artistically expressive visualizations can be made to be reusable.

The work presents a method to enable matching of level-of-detail (LOD) models to image-plane resolution over large variations in viewing distances often present in exterior images. A relationship is developed between image sampling rate, viewing distance, object projection, and expected image error due to LOD approximations. This is employed in an error metric to compute error profiles for LOD models. Multirate filtering in the frequency space of a reference object image is utilized to approximate multiple distant views over a range of orientations. An importance sampling method is described to better characterize perspective projection over view distance. A contrast sensitivity function (CSF) is employed to approximate the response of the vision system. Examples are presented for multiresolution spheres and a terrain height field feature. Future directions for extending this method are described.

We present a new technique for extracting regions of interest (ROI) applying a local watershed transformation. The proposed strategy for computing catchment basins in a given region of interest is based on a rain-falling simulation. Unlike the standard watershed algorithms, which flood the complete (gradient magnitude of an) image, the proposed approach allows us to perform this task locally. Thus, a controlled region growth is performed, saving time and reducing the memory requirement especially when applied on volume data. A second problem arising from the standard watershed transformation is the over-segmented result and the lack of sound criteria for merging the computed basins. For overcoming this drawback, we present a basin-merging strategy introducing four criteria for merging adjacent basins. The threshold values applied in this strategy are derived from the user input and match rather the attributes of the selected object than of all objects in the image. In doing so, the user is not required to adjust abstract numbers, but to simply select a coarse region of interest. Moreover, the proposed algorithm is not limited to the 2D case. As we show in this work, it is suitable for volume data processing as well. Finally, we present the results of applying the proposed approach on several example images and volume data sets.

The concept of fairing applied to irregular triangular meshes has become more and more important. Previous contributions constructed better fairing operators, and applied them both to multiresolution editing tools and to multiresolution representations of meshes. In this paper, we generalize these powerful techniques to handle non-manifold models. Our framework computes a multilevel fairing of models by fairing both the two-manifold surfaces that define the model, the so-called two features, and all the boundary and intersection curves of the model, the so-called one-features. In addition we introduce two extensions that can be used in our framework as well as in manifold fairing concepts: an exact local volume preservation strategy and a method for feature preservation. Our framework works with any of the manifold fairing operators for meshes.

Visualization can be an important tool for displaying, categorizing and digesting large quantities of inter-related information during laboratory and simulation experiments. Summary visualizations that compare and represent data sets in the context of a collection are particularly valuable. Applicable visualizations used in these settings must be fast (near real time) and should allow the addition of data sets as they are acquired without requiring rerendering of the visualization. This paper examines several visualization techniques for representing collections of data sets in a combustion experiment including spectral displays, tiling and geometric mappings of symmetry. The application provides insight into how such visualizations might be used in practical real-time settings to assist in exploration and in conducting parameter space surveys.

Splatting is widely applied in many areas, including volume, point-based and image-based rendering. Improvements to splatting, such as eliminating popping and color bleeding, occasion-based acceleration, post-rendering classification and shading, have all been recently accomplished. These improvements share a common need for efficient frame-buffer accesses. We present an optimized software splatting package, using a newly designed primitive, called FastSplat, to scan-convert footprints. Our approach does not use texture mapping hardware, but supports the whole pipeline in memory. In such an integrated pipeline, we are then able to study the optimization strategies and address image quality issues. While this research is meant for a study of the inherent trade-off of splatting, our renderer, purely in software, achieves 3- to 5-fold speedups over a top-end texture hardware implementation (for opaque data sets). We further propose a method of efficient occlusion culling using a summed area table of opacity. 3D solid texturing and bump mapping capabilities are demonstrated to show the flexibility of such an integrated rendering pipeline. A detailed numerical error analysis, in addition to the performance and storage issues, is also presented. Our approach requires low storage and uses simple operations. Thus, it is easily implementable in hardware.