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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,...
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...
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...
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...
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. Although, 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...
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...
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...
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,...
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...
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...
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...
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...
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...
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...
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...
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,...
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...
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...
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...
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