Browsing by Author "Berk, Hakan"

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Open Access
Direct volume rendering of unstructured grids
(Pergamon Press, 2003) Berk, Hakan; Aykanat, Cevdet; Güdükbay, Uğur
This paper investigates three categories of algorithms for direct volume rendering of unstructured grids, which are image-space, object-space, and hybrid methods. We propose three new algorithms. Cell Projection algorithm, which falls into object-space category, is capable of rendering non-convex meshes through a simple yet efficient sorting schema that exploits both image and object space coherencies. Existing hybrid methods use object-then-image traversal order that enforces the processing of each cell. Thus, these algorithms perform redundant operations and do not support early ray termination. We propose a hybrid method, called Span-Buffer Ray Casting (SBRC), that can support early ray termination discarding redundant operations by employing image-then-object traversal order. Another hybrid method, called Koyamada-SBRC (K-SBRC), is proposed with the motivation of refining image-space and hybrid methods to extract the best features of them. This method is developed by blending SBRC approach with Koyamada's algorithm, which is an efficient image-space algorithm. All proposed algorithms are capable of handling acyclic non-convex meshes and generating images of acceptable quality. SBRC and K-SBRC algorithms have the additional capabilities of rendering cyclic meshes and supporting early ray termination. The proposed algorithms and Koyamada's algorithm are implemented and experimented in a common framework for analyzing their relative performance. © 2003 Elsevier Science Ltd. All rights reserved.
Open Access
Fast direct volume rendering of unstructured grids
(1997-09) Berk, Hakan
Scientific 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.