Browsing by Subject "Volume visualization"
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Item Open Access Dynamic view-dependent visualization of unstructured tetrahedral volumetric meshes(Springer, 2012) Okuyan, E.; Güdükbay, Uğur; Işler, V.Visualization of large volumetric datasets has always been an important problem. Due to the high computational requirements of volume-rendering techniques, achieving interactive rates is a real challenge. We present a selective refinement scheme that dynamically refines the mesh according to the camera parameters. This scheme automatically determines the impact of different parts of the mesh on the output image and refines the mesh accordingly, without needing any user input. The view-dependent refinement scheme uses a progressive mesh representation that is based on an edge collapse-based tetrahedral mesh simplification algorithm. We tested our view-dependent refinement framework on an existing state-of-theart volume renderer. Thanks to low overhead dynamic view-dependent refinement, we achieve interactive frame rates for rendering common datasets at decent image resolutions. © 2012 The Visualization Society of Japan.Item Open Access Fast direct volume rendering of unstructured grids(1997-09) Berk, HakanScientific computing has become more and more important with the evolving technology. The vast amount of data that the scientific computing applications produce need new ways to be processed and interpreted by scientists. The large amount of data makes it very difficult for scientists to extract useful information from the data, and interpret it to reach a useful conclusion. Thus. visualization of such numerical data as an image, which is known as Scientific Visualization, is an indispensable tool for researchers. Volume Rendering is a very important branch of Scientific Visualization and makes it possible for scientists to visualize the 3-dimensional (3D) volumetric datasets. Volume Rendering algorithms can be classified into two categories: Indirect and Direct methods. Indirect methods are faster, but direct methods are more flexible and acurate. Direct methods can be classified into three categories: image-space (ray-casting), object-space (projection) and hybrid. The efficiency of a direct volume rendering (DVR) algorithm is strongly related to the way that it solves the underlying point location and view sort problems. Although these problems are almost trivial ones to solve in structured grids, they become more complex ones to deal with for unstructured grids. Researchers have tried to speed up the volume rendering of unstructured grids by using special graphics hardware, and parallel architectures, but the need for software solutions to these problems will always exist. These thesis is involved in solving those problems in unstructured grids via software methods. It investigates three distinct categories, namely image-space methods, object-space methods and hybrid methods for fast direct volume rendering of unstructured grids. The main objective of the thesis is to identify the relative superiorities and inferiorities of the algorithms in these three categories. A survey of existing methods is enriched by a discussion of their merits and shortcomings. Three new and fast algorithms to overcome the existing inefficiencies are proposed, and one existing algorithm is investigated in detail for better comparision. All of the proposed algorithms are aimed at producing correct, high quality images. Two of the proposed algorithms are pure ray-casting based solutions that support early ray termination and can handle cyclic grids. The relative performances of the proposed algorithms are experimented on a wide range of benchmark grids in a common framework for software methods and they are found to be faster than the existing best DVR algorithms.Item Open Access Volumetric rendering techniques for scientific visualization(2014) Okuyan, ErhanDirect volume rendering is widely used in many applications where the inside of a transparent or a partially transparent material should be visualized. We have explored several aspects of the problem. First, we proposed a view-dependent selective refinement scheme in order to reduce the high computational requirements without affecting the image quality significantly. Then, we explored the parallel implementations of direct volume rendering: both on GPU and on multi-core systems. Finally, we used direct volume rendering approaches to create a tool, MaterialVis, to visualize amorphous and/or crystalline materials. Visualization of large volumetric datasets has always been an important problem. Due to the high computational requirements of volume-rendering techniques, achieving interactive rates is a real challenge. We present a selective refinement scheme that dynamically refines the mesh according to the camera parameters. This scheme automatically determines the impact of different parts of the mesh on the output image and refines the mesh accordingly, without needing any user input. The viewdependent refinement scheme uses a progressive mesh representation that is based on an edge collapse-based tetrahedral mesh simplification algorithm. We tested our view-dependent refinement framework on an existing state-of-the-art volume renderer. Thanks to low overhead dynamic view-dependent refinement, we achieve interactive frame rates for rendering common datasets at decent image resolutions. Achieving interactive rates for direct volume rendering of large unstructured volumetric grids is a challenging problem, but parallelizing direct volume rendering algorithms can help achieve this goal. Using Compute Unified Device Architecture (CUDA), we propose a GPU-based volume rendering algorithm that itself is based on a cell projection-based ray-casting algorithm designed for CPU implementations. We also propose a multi-core parallelized version of the cell-projection algorithm using OpenMP. In both algorithms, we favor image quality over rendering speed. Our algorithm has a low memory footprint, allowing us to render large datasets. Our algorithm support progressive rendering. We compared the GPU implementation with the serial and multi-core implementations. We observed significant speed-ups, that, together with progressive rendering, enabling reaching interactive rates for large datasets. Visualization of materials is an indispensable part of their structural analysis. We developed a visualization tool for amorphous as well as crystalline structures, called MaterialVis. Unlike the existing tools, MaterialVis represents material structures as a volume and a surface manifold, in addition to plain atomic coordinates. Both amorphous and crystalline structures exhibit topological features as well as various defects. MaterialVis provides a wide range of functionality to visualize such topological structures and crystal defects interactively. Direct volume rendering techniques are used to visualize the volumetric features of materials, such as crystal defects, which are responsible for the distinct fingerprints of a specific sample. In addition, the tool provides surface visualization to extract hidden topological features within the material. Together with the rich set of parameters and options to control the visualization, MaterialVis allows users to visualize various aspects of materials very efficiently as generated by modern analytical techniques such as the Atom Probe Tomography.