Voxelbasert 3D visualisering i OpenGL

This thesis deals with volume rendering in OpenGL and looks at the different areas at which 3D modeling and visualization is used. The thesis focuses on voxel rendering, its advantages and drawbacks, and also the implementation of such a renderer. The aim of the thesis was to develop a voxel renderer in OpenGL from scratch, to a fully functional application that could visualize different 3D data sets generated from for example Diffpack. The data sets are scalar fields which are visualized by associating transparency and color to voxels from the values in the data sets. There are multiple ways to visualize voxels, I have mainly used a method that uses textures mapped to a 2D plane, which are assembled into a 3D voxel set. This is a method that is supported by common 3D hardware. To get maximum performance from the different 3D graphics cards that are available, you can use different graphics libraries. For PC’s there are two low-level graphics libraries to choose from, OpenGL and DirectX. OpenGL is developed by Silicon Graphics and are compatible with a number of different operating systems. DirectX is developed by Microsoft and is only supported in Microsoft Windows. For this thesis I chose OpenGL as the tool to use. OpenGL is a powerful software library which utilizes modern graphics hardware. Through OpenGL you get access to most of the graphic cards functions. OpenGL is however a low-level library and demands a lot of knowledge on a fundamental level to be able to visualize complex objects and scenes. I therefore take a closer look at how OpenGL works and at the theory at which it is built. I also look at the opportunities, advantages and drawbacks with voxel rendering, and looks at the requirements which is demanded by the hardware to be able to solve the tasks efficiently. I conclude this thesis by comparing my OpenGL voxel renderer with other available voxel renderers, such as The Visualization Toolkit (VTK)

Three dimensional flame reconstruction towards the study of fire-induced transmission line flashovers.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.The work presented in this thesis focuses on the problem of reconstructing threedimensional models of fire from real images. The intended application of the reconstructions is for use in research into the phenomenon of fire-induced high voltage flashover, which, while a common problem, is not fully understood. As such the reconstruction must estimate not only the geometry of the flame but also the internal density structure, using only a set of a few synchronised images. Current flame reconstruction techniques are investigated, revealing that relatively little work has been done on the subject, and that most techniques follow either an exclusively geometric or tomographic direction. A novel method, termed the 3D Fuzzy Hull method, is proposed, incorporating aspects of tomography, statistical image segmentation and traditional object reconstruction techniques. By using physically based principles the flame images are related to the relative flame density, allowing the problem to be tackled from a tomographic perspective. A variation of algebraic tomography is then used to estimate the internal density field of the flame. This is done within a geometric framework by integrating the fuzzy c-means image segmentation technique and the visual hull concept into the process. Results are presented using synthetic and real flame image sets

3-D FULLY POLARIMETRIC WIDE-ANGLE SUPERRESOLUTION-BASED SAR IMAGING FOR ATR

This paper discusses four topics, using the publicly released AFRL X-band backhoe “datadome”, as well as our own UHF backhoe datadome. First we show that wide-angle SAR apertures, ideally spanning 360 ◦ in azimuth with dense elevation coverage, combined with volumetric backprojection imaging, yield imagery that bears a strong literal resemblance to the target, facilitating both human and automatic target recognition. Second, we illustrate how 3-D “superresolution ” imaging techniques can improve sharpness and reduce speckle, just as they do for 2-D imagery. Third, we illustrate that by imaging over a hemispheric aperture, resolution can be improved substantially beyond the conventional smallangle levels. Fourth, we expand upon the third point and show that a hypothetical monostatic UHF system (300MHz BW centered at 600MHz with sparsely-sampled hemispheric aperture) can yield imagery with comparable spatial detail to a monostatic Xband (1.2GHz BW centered at 10GHz with 7 ◦ × 7 ◦ az/el aperture) system. Unlike the X-band system, the UHF system sees all monostatic target scattering, and provides a more complete target image. Bandwidth interpolation/extrapolation methods such as Least-Squares SuperResolution (LSSR) mitigate the glint and sidelobe artifacts that accompany the use of sparse az/el apertures. 1