Detlev Stalling

Fast and resolution independent line integral convolution

Line Integral Convolution (LIC) is a powerful technique for generating striking images and animations from vector data. Introduced in 1993, the method has rapidly found many application areas, ranging from computer arts to scientific visualization. Based upon locally filtering an input texture along a curved stream line segment in a vector field, it is able to depict directional information at high spatial resolutions. We present a new method for computing LIC images, which minimizes the total number of stream lines to be computed and thereby reduces computational costs by an order of magnitude compared to the original algorithm. Our methods utilizes fast, error-controlled numerical integrators. Decoupling the characteristic lengths in vector field grid, input texture and output image, it allows to compute filtered images at arbitrary resolution. This feature is of great significance in computer animation as well as in scientific visualization, where it can be used to explore vector data by smoothly enlarging structure of details. We also present methods for improved texture animation, employing constant filter kernels only. To obtain an optimal motion effect, spatial decay of correlation between intensities of distant pixels in the output image has to be controlled. This is achieved by blending different phase shifted box filter animations and by adaptively rescaling the contrast of the output frames.

38 – amira: A Highly Interactive System for Visual Data Analysis

The software system Amira has been designed to close the gap among the ease of use, power, interactivity of monolithic special-purpose software, and the flexibility and extensibility of data-flow-oriented visualization environments. One major focus of the software is the visualization and analysis of volumetric data, which is common in medicine, biology, and microscopy. With Amira, volumes can be displayed and segmented, 3D polygonal models can be reconstructed, and these models can be further processed and converted into tetrahedral volume grids. Due to its flexible design, Amira can also perform many other tasks, including finite-element postprocessing, flow visualization, and visualization of molecules. This chapter discusses the fundamental concepts, techniques, and features of Amira.

Interactive visualization of 3D-vector fields using illuminated stream lines

A new technique for interactive vector field visualization using large numbers of properly illuminated stream lines is presented. Taking into account ambient, diffuse, and specular reflection terms as well as transparency, we employ a realistic shading model which significantly increases quality and realism of the resulting images. While many graphics workstations offer hardware support for illuminating surface primitives, usually no means for an accurate shading of line primitives are provided. However, we show that proper illumination of lines can be implemented by exploiting the texture mapping capabilities of modern graphics hardware. In this way high rendering performance with interactive frame rates can be achieved. We apply the technique to render large numbers of integral curves in a vector field. The impression of the resulting images can be further improved by making the curves partially transparent. We also describe methods for controlling the distribution of stream lines in space. These methods enable us to use illuminated stream lines within an interactive visualization environment.

Fast and Intuitive Generation of Geometric Shape Transitions

We describe a novel method for continuously transforming two triangulated models of arbitrary topology into each other. Equal global topology for both objects is assumed. However, extensions for genus changes during metamorphosis are provided. The proposed method addresses the major challenge in 3D metamorphosis, namely, specifying the morphing process intuitively with minimal user interaction and sufficient detail. Corresponding regions and point features are interactively identified. These regions are parametrized automatically and consistently, providing a basis for smooth interpolation. Suitable 3D interaction techniques offer a simple and intuitive control over the whole morphing process.

Fast display of illuminated field lines

A new technique for interactive vector field visualization using large numbers of properly illuminated field lines is presented. Taking into account ambient, diffuse and specular reflection terms, as well as transparency and depth cueing, we employ a realistic shading model which significantly increases the quality and realism of the resulting images. While many graphics workstations offer hardware support for illuminating surface primitives, usually no means for an accurate shading of line primitives are provided. However, we show that proper illumination of lines can be implemented by exploiting the texture mapping capabilities of modern graphics hardware. In this way, high rendering performance with interactive frame rates can be achieved. We apply the technique to render large numbers of integral curves of a vector field. The impression of the resulting images can be further improved by a number of visual enhancements, like color coding or particle animation. We also describe methods for controlling the distribution of field lines in space. These methods enable us to use illuminated field lines for interactive exploration of vector fields.

Fast line integral convolution for arbitrary surfaces in 3D

We describe an extension of the line integral convolution method (LIC) for imaging of vector fields on arbitrary surfaces in 3D space. Previous approaches were limited to curvilinear surfaces, i.e. surfaces which can be parametrized globally using 2D-coordinates. By contrast our method also handles the case of general, possibly multiply connected surfaces. The method works by tesselating a given surface with triangles. For each triangle local euclidean coordinates are defined and a local LIC texture is computed. No scaling or distortion is involved when mapping the texture onto the surface. The characteristic length of the texture remains constant.

Parallel line integral convolution

Line integral convolution (LIC) is a powerful method for computing directional textures from vector data. LIC textures can be animated, yielding the effect of flowing motion. Both, static images and animation sequences are of great significance in scientific visualization. Although an efficient algorithm for computing static LIC textures is known, the generation of animation sequences still requires a considerable amount of computing time. In this paper we propose an algorithm for computing animation sequences on a massively parallel distributed memory computer. With this technique it becomes possible to utilise animated LIC for interactive vector field visualization. To take advantage of the strong temporal coherence between different frames, parallelization is performed in image space rather than in time. Image space coherence is exploited using a flexible update and communication scheme. In addition algorithmic improvements on LIC are proposed that can be applied to parallel and sequential algorithms as well.

Fast LIC with Piecewise Polynomial Filter Kernels

Line integral convolution (LIC) has become a well-known and popular method for visualizing vector fields. The method works by convolving a random input texture along the integral curves of the vector field. In order to accelerate image synthesis significantly, an efficient algorithm has been proposed that utilizes pixel coherence in field line direction. This algorithm, called “fast LIC”, originally was restricted to simple box-type filter kernels.

Experimental and Numerical Dye Washout Flow Visualization: Flow analysis in the realistic model of pathologic artery enlargement (aneurysm)

Flow visualization in realistic models is very important for the study of pathological vessel enlargements (aneurysms). Furthermore, flow visualization may help in treatment decisions. However, the most interesting parameter, the wall shear stress, is difficult to measure in vivo. This parameter can be provided by computational fluid dynamics. However, the numerical methods don’t visualize the results as does of the dye washout method — a method often used in flow studies. This experimental method simulates the cine angiograms acquired during contrast agent injection used in medicine. In this paper we present the dye washout visualization of CFD results and compare these results with the conventional dye washout experiments in the same aneurysm model under steady flow conditions.

Numerical dye washout method as a tool for characterizing the heart valve flow: study of three standard mechanical heart valves.

To date, no ideal heart valve prosthesis for the replacement of a diseased natural valve or for use in ventricular assist devices exists. Valves still cause thromboembolic complications originating from thrombus formations in the valve’s stagnant and recirculation zones. Optimization of valve design requires detailed flow field investigations. Usually, the regions that are more prone to thrombus formation can be estimated using a dye washout experiment. This successful experimental method was simulated using numerical methods. The proposed method was applied to three standard mechanical heart valves—Björk-Shiley, St-Jude, and Starr-Edwards valve. The dye washout was characterized by a time course of the gray value averaged over a defined region of interest. Finally, these curves were quantified by a half dye time (HDT), which characterizes the blood residence time. The HDT in the best valve, the Starr-Edwards valve, was 0.0747 s. The HDT in the worst valve, the Björk-Shiley, was 0.0942 s. The analysis of the hemodynamic valve parameters (pressure drop, velocity magnitudes and turbulence) revealed that the best valve is the St-Jude valve. The Starr-Edwards valve displayed the worst hemodynamic parameters. This study shows that the proposed numerical method of dye washout visualization can be used as an additional tool for the flow characterization.