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Date 8-13 Oct. 2000

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Displaying Results 1 - 25 of 66
  • Proceedings Visualization 2000. VIS 2000 (Cat. No.00CH37145)

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    Freely Available from IEEE
  • Extracting regions of interest applying a local watershed transformation

    Page(s): 21 - 28
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    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. View full abstract»

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  • A visibility determination algorithm for interactive virtual endoscopy

    Page(s): 29 - 36
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    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. View full abstract»

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  • 3D digital cleansing using segmentation rays

    Page(s): 37 - 44
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    We propose a novel approach for segmentation and digital cleansing of endoscopic organs. Our method can be used for a variety of segmentation needs with little or no modification. It aims at fulfilling the dual and often conflicting requirements of a fast and accurate segmentation and also eliminates the undesirable partial volume effect which contemporary approaches cannot. For segmentation and digital cleansing, we use the peculiar characteristics exhibited by the intersection of any two distinct-intensity regions. To detect these intersections we cast rays through the volume, which we call the segmentation rays as they assist in the segmentation. We then associate a certain task of reconstruction and classification with each intersection the ray detects. We further use volumetric contrast enhancement to reconstruct surface lost by segmentation (if any), which aids in improving the quality of the volume rendering. View full abstract»

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  • CEASAR: a smooth, accurate and robust centerline extraction algorithm

    Page(s): 45 - 52
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    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. View full abstract»

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  • H-BLOB: a hierarchical visual clustering method using implicit surfaces

    Page(s): 61 - 68
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    We present a new hierarchical clustering and visualization algorithm called H-BLOB, which groups and visualizes cluster hierarchies at multiple levels-of-detail. Our method is fundamentally different to conventional clustering algorithms, such as C-means, K-means, or linkage methods that are primarily designed to partition a collection of objects into subsets sharing similar attributes. These approaches usually lack an efficient level-of-detail strategy that breaks down the visual complexity of very large datasets for visualization. In contrast, our method combines grouping and visualization in a two stage process constructing a hierarchical setting. In the first stage a cluster tree is computed making use of an edge contraction operator. Exploiting the inherent hierarchical structure of this tree, a second stage visualizes the clusters by computing a hierarchy of implicit surfaces. We believe that H-BLOB is especially suited for the visualization of very large datasets and for visual decision making in information visualization. The versatility of the algorithm is demonstrated using examples from visual data mining. View full abstract»

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  • A spreadsheet interface for visualization exploration

    Page(s): 69 - 76
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    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. View full abstract»

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  • Procedural annotation of uncertain information

    Page(s): 77 - 84
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    In many applications of scientific visualization, a large quantity of data is being processed and displayed in order to enable a viewer to make informed and effective decisions. Since little data is perfect, there is almost always some degree of associated uncertainty. This uncertainty is an important part of the data and should be taken into consideration when interpreting the data. Uncertainty, however, should not overshadow the data values. Many methods that address the problem of visualizing data with uncertainty can distort the data and emphasize areas with uncertain values. We have developed a method for showing the uncertainty information together with data with minimal distraction. This method uses procedurally generated annotations which are deformed according to the uncertainty information. As another possible technique we propose distorting glyphs according to the uncertainty information. View full abstract»

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  • Simplification of tetrahedral meshes with accurate error evaluation

    Page(s): 85 - 92
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    The techniques for reducing the size of a volume dataset by preserving both the geometrical/topological shape and the information encoded in an attached scalar field are attracting growing interest. Given the framework of incremental 3D mesh simplification based on edge collapse, we propose an approach for the integrated evaluation of the error introduced by both the modification of the domain and the approximation of the field of the original volume dataset. We present and compare various techniques to evaluate the approximation error or to produce a sound prediction. A flexible simplification tool has been implemented, which provides a different degree of accuracy and computational efficiency for the selection of the edge to be collapsed. Techniques for preventing a geometric or topological degeneration of the mesh are also presented. View full abstract»

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  • Tetrahedron based, least squares, progressive volume models with application to freehand ultrasound data

    Page(s): 93 - 100
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    We present a new method for the modeling of freehand collected three-dimensional ultrasound data. The model is piecewise linear and based upon progressive tetrahedral domains created by a subdivision scheme which splits a tetrahedron on on its longest edge and guarantees a valid tetrahedrization. Least squares error is used to characterize the model and an effective iterative technique is used to compute the values of the model at the vertices of the tetrahedral grid. Since the subdivision strategy is adaptive, the complexity of the model conforms to the complexity of the data leading to an extremely efficient and highly compressed volume model. The model is evaluated in real time using piecewise linear interpolation, and gives a medical professional the chance to see images which would not be possible using conventional ultrasound techniques. View full abstract»

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  • On-the-fly rendering of losslessly compressed irregular volume data

    Page(s): 101 - 108
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    Very large irregular-grid data sets are represented as tetrahedral meshes and may incur significant disk I/O access overhead in the rendering process. An effective way to alleviate the disk I/O overhead associated with rendering a large tetrahedral mesh is to reduce the I/O bandwidth requirement through compression. Existing tetrahedral mesh compression algorithms focus only on compression efficiency and cannot be readily integrated into the mesh rendering process, and thus demand that a compressed tetrahedral mesh be decompressed before it can be rendered into a 2D image. This paper presents an integrated tetrahedral mesh compression and rendering algorithm called Gatun, which allows compressed tetrahedral meshes to be rendered incrementally as they are being decompressed, thus leading to an efficient irregular grid rendering pipeline. Both compression and rendering algorithms in Gatun exploit the same local connectivity information among adjacent tetrahedra, and thus can be tightly integrated into a unified implementation framework. Our tetrahedral compression algorithm is specifically designed to facilitate the integration with an irregular grid renderer without any compromise in compression efficiency. A unique performance advantage of Gatun is its ability to reduce the runtime memory footprint requirement by releasing memory allocated to tetrahedra as early as possible. View full abstract»

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  • Hardware-accelerated volume and isosurface rendering based on cell-projection

    Page(s): 109 - 116
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    We present two beneficial rendering extensions to the projected tetrahedra (PT) algorithm proposed by Shirley and Tuchman (1990). These extensions are compatible with any cell sorting technique, for example the BSP-XMPVO sorting algorithm for unstructured meshes. Using 3D texture mapping our first extension solves the longstanding problem of hardware-accelerated but accurate rendering of tetrahedral volume cells with arbitrary transfer functions. By employing 2D texture mapping our second extension realizes the hardware-accelerated rendering of multiple shaded isosurfaces within the PT algorithm without reconstructing the isosurfaces. Additionally, two methods are presented to combine projected tetrahedral volumes with isosurfaces. The time complexity of all our algorithms is linear in the number of tetrahedra and does neither depend on the number of isosurfaces nor on the employed transfer functions. View full abstract»

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  • Achieving color uniformity across multi-projector displays

    Page(s): 117 - 124
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    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). View full abstract»

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  • Automatic alignment of high-resolution multi-projector displays using an uncalibrated camera

    Page(s): 125 - 130
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    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. View full abstract»

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  • Shock and vortex visualization using a combined visual/haptic interface

    Page(s): 131 - 137
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    Specific rendering modes are developed for a combined visual/haptic interface to allow exploration and understanding of fluid dynamics data. The focus is on visualization of shock surfaces and vortex cores. Advantages provided by augmenting traditional graphical rendering modes with haptic rendering modes are discussed. Particular emphasis is placed on synergistic combinations of visual and haptic modes which enable rapid, exploratory interaction with the data. Implementation issues are also discussed. View full abstract»

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  • Six degree-of-freedom haptic display of polygonal models

    Page(s): 139 - 146
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    We present an algorithm for haptic display of moderately complex polygonal models with a six degree of freedom (DOF) force feedback device. We make use of incremental algorithms for contact determination between convex primitives. The resulting contact information is used for calculating the restoring forces and torques and thereby used to generate a sense of virtual touch. To speed up the computation, our approach exploits a combination of geometric locality, temporal coherence, and predictive methods to compute object-object contacts at kHz rates. The algorithm has been implemented and interfaced with a 6-DOF PHANToM Premium 1.5. We demonstrate its performance on force display of the mechanical interaction between moderately complex geometric structures that can be decomposed into convex primitives. View full abstract»

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  • A level-set method for flow visualization

    Page(s): 147 - 154
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    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. View full abstract»

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  • Hardware-accelerated texture advection for unsteady flow visualization

    Page(s): 155 - 162
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    We present a novel hardware-accelerated texture advection algorithm to visualize the motion of two-dimensional unsteady flows. Making use of several proposed extensions to the OpenGL-1.2 specification, we demonstrate animations of over 65,000 particles at 2 frames/sec on an SGI Octane with EMXI graphics. High image quality is achieved by careful attention to edge effects, noise frequency, and image enhancement. We provide a detailed description of the hardware implementation, including temporal and spatial coherence techniques, dye advection techniques, and feature extraction. View full abstract»

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  • A flow-guided streamline seeding strategy

    Page(s): 163 - 170
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    The paper presents a seed placement strategy for streamlines based on flow features in the dataset. The primary goal of our seeding strategy is to capture flow patterns in the vicinity of critical points in the flow field, even as the density of streamlines is reduced. Secondary goals are to place streamlines such that there is sufficient coverage in non-critical regions, and to vary the streamline placements and lengths so that the overall presentation is aesthetically pleasing (avoid clustering of streamlines, avoid sharp discontinuities across several streamlines, etc.). The procedure is straightforward and non-iterative. First, critical points are identified. Next, the flow field is segmented into regions, each containing a single critical point. The critical point in each region is then seeded with a template depending on the type of critical point. Finally, additional seed points are randomly distributed around the field using a Poisson disk distribution to minimize closely spaced seed points. The main advantage of this approach is that it does not miss the features around critical points. Since the strategy is not image-guided, and hence not view dependent, significant savings are possible when examining flow fields from different viewpoints, especially for 3D flow fields. View full abstract»

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  • Enabling level-of-detail matching for exterior scene synthesis

    Page(s): 171 - 178
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    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. View full abstract»

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  • Basic research for coloring multichannel MRI data

    Page(s): 187 - 194
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    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. View full abstract»

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  • Volume illustration: non-photorealistic rendering of volume models

    Page(s): 195 - 202
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    Accurately and automatically conveying the structure of a volume model is a problem that has not been fully solved by existing volume rendering approaches. Physics-based volume rendering approaches create images which may match the appearance of translucent materials in nature but may not embody important structural details. Transfer function approaches allow flexible design of the volume appearance but generally require substantial hand-tuning for each new data set in order to be effective. We introduce the volume illustration approach, combining the familiarity of a physics-based illumination model with the ability to enhance important features using non-photorealistic rendering techniques. Since the features to be enhanced are defined on the basis of local volume characteristics rather than volume sample values, the application of volume illustration techniques requires less manual tuning than the design of a good transfer function. Volume illustration provides a flexible unified framework for enhancing structural perception of volume models through the amplification of features and the addition of illumination effects. View full abstract»

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  • Pen-and-ink rendering in volume visualisation

    Page(s): 203 - 210
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    Concerns the development of non-photorealistic rendering techniques for volume visualisation. In particular, we present two pen-and-ink rendering methods, a 3D method based on non-photorealistic solid textures, and a 2+D method that involves two rendering phases in the object space and the image space respectively. As both techniques utilize volume- and image-based data representations, they can be built upon a traditional volume rendering pipeline, and can be integrated with the photorealistic methods available in such a pipeline. We demonstrate that such an integration facilitates an effective mechanism for enhancing visualisation and its interpretation. View full abstract»

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  • Two-level volume rendering - fusing MIP and DVR

    Page(s): 211 - 218
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    Presents a two-level approach for fusing direct volume rendering (DVR) and maximum-intensity projection (MIP) within a joint rendering method. Different structures within the data set are rendered locally by either MIP or DVR on an object-by-object basis. Globally, all the results of subsequent object renderings are combined in a merging step (usually compositing in our case). This allows us to selectively choose the most suitable technique for depicting each object within the data, while keeping the amount of information contained in the image at a reasonable level. This is especially useful when inner structures should be visualized together with semi-transparent outer parts, similar to the focus-and-context approach known from information visualization. We also present an implementation of our approach which allows us to explore volumetric data using two-level rendering at interactive frame rates. View full abstract»

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  • FastSplats: optimized splatting on rectilinear grids

    Page(s): 219 - 226
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    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. View full abstract»

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