Browsing by Subject "Three-dimensional imaging"
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Item Automatic detection of bends in louvers using range imaging(Texas Tech University, 2004-12) Shah, Utpal D.Shutters have become an important part of home decor. Quality of shutters depends on how much light it lets through after it is closed. Shutters let light through because the louvers used to construct them are not straight. To this end, it is important to detect bends in louvers before they are used in constmction of shutters. Current methods of detecting bends are subjective and inadequate. So, we have proposed a laser-based imaging system that utilizes a smart camera to acquire 3-D range images of the louver samples. In this system, we use range images to detect the 'dome points,' which follows the shape of the louver accurately, using a peak detection algorithm. The system also incorporates methods based on polynomial curve-fitting and scale-space filtering that ultimately detects the location of the bends. First, we fit a polynomial curve to reduce the noise in the dome points, followed by scale-space filtering to locate the extrema of the curve. Finally, we relate the extrema of the curve to the locations of the bends in the louver. We tested our method on 39 samples of louvers with varied lengths and compared the results with the results collected from ground tmth. Results are comparable as they resulted in high correlation coefficient between the two methods.Item Geospatial description of river channels in three dimensions(2004) Merwade, Venkatesh; Maidment, David R.Data describing the three-dimensional structure of river channels are required for hydrodynamic simulation, water quality modeling and flood inundation mapping. However, unlike land surface terrain, there is no standardized three-dimensional geospatial representation of river channel morphology. In addition, the bathymetry data that are used to describe the threedimensional structure of river channels are collected only on short reaches, and are usually not available for the entire stream network at a regional scale. The research presented in this dissertation deals with the standardized geospatial description of river channels in GIS at both local and regional scales. At a local scale, where the bathymetry data are available, a procedure is developed that uses the curvilinear orthogonal coordinate system approach to create a threedimensional structure of river channels in the form of cross-sections (ground profiles transverse to flow) and profile-lines (ground profiles parallel to flow). To describe the channel bathymetry at regional scale, an analytical model is developed that uses locally collected field data on the Brazos River in Texas and readily available regional scale data such as the hydrography data. The analytical model, called the River Channel Morphology Model (RCMM), is based on deriving relationships among different channel characteristics such as the channel planform (shape of the channel), the thalweg location, and the cross-sections. Then, using only the channel planform, in conjunction with the derived relationships, it is possible to create a three-dimensional channel morphology that comprises a mesh of cross-sections and profile-lines. The three-dimensional mesh at the regional scale, however, provides only a mean surface for the channel bed. Although the results from RCMM are promising, it is limited by its ability to model all the variables that are involved in the development of complex river geometry. Bathymetry data collected on the Brazos, Guadalupe, and Sulphur Rivers in Texas are used to demonstrate the applicability of the theories presented in this dissertation. It is learned that creating an accurate description of river channel geometry is a complex problem, which requires knowledge about channel planform, discharge, geology, geomorphologic features such as pools and riffles, and small-scale stochastic variations to solve.Item Pyramidal stereo matching and optimal surface recovery for 3-D visualization(Texas Tech University, 2002-08) Corona, EnriqueThree-dimensional surface recovery based on a pair of stereoscopic images is a very well-known ill-posed problem with solutions depending mainly on the correct measures of the shifts between corresponding points (disparities) in the images acquired by a known imaging system. Noise, occlusions, and distortion present in the pair of images make the task of finding precise disparities difficult and very time consuming. This work presents a three-dimensional surface restoration method based on the recovery of the optimum surface within a 3-D cross-correlation coefficient volume via a two-stage dynamic programming technique. This procedure is applied to a set of optic nerve head (ONH) images, which are used for finding clinical measures of progression of glaucoma. Registration of these types of images is performed through a two-step coarse-to- fine procedure using power cepstrum and cross-correlation operations, while a local registration based on the weighted mean of second-degree polynomials is used for image fitting. Variations in topography of the ONH can be measured through cup-to-disc ratios which are computed from the 3-D surface generated from longitudinal stereo disc photographs of glaucoma patients spanning several years. These computer-generated measures of cup-to-disc volume ratios correlate well with the traditional stereo cup-to-disc ratios manually computed from clinical interpretations. Such algorithmic approach to semi-automated computation of cup-to-disc volume ratios may potentially provide a more precise and repeatable measure of progression of glaucoma than the existing clinical measures. Moreover, the 3-D surface recovery technique developed in this thesis may provide a general technique for visualizing 3-D objects in a natural scene.Item The digital reflection: implications of three-dimensional laser scanning technology on historic architecture documentation(Texas Tech University, 2001-08) Bagchi, Sumantra; Hill, Glenn E.; Bilello, Joseph; White, John P.How can laser scanning technology be used to document a historical structure in such a way that the duration of the process is reduced and made less labor intensive, with the quality of documentation being equal to, or better than that required by the Historic American Buildings Survey (HABS), and that archival storage methods and accessibility to the public are enhanced? 3D Laser Scanning is a relatively new technique whereby pulses of light from a fixed source measure the exact co-ordinate position of points on a structure or object. This group or "cloud of points" accurately represents the object in three-dimensional virtual space. The application of 3D laser scanning technology to historic documentation in Texas Tech University was first examined in the measured drawing process of the JA Ranch, in Palo Duro Canyon, Texas. In this study, I described what eventuated and then analyzed a case study of this process with respect to time, labor, quality and image accessibility. This study had two steps. The first was to identify problems with the process that was followed, and the second was to suggest possible solutions in achieving an efficient procedure. The outcome of the case study analysis resulted in the delineation of an optimal course, which is replicable for a structure of comparable complexity.Item The digital reflection: implications of three-dimensional laser scanning technology on historic architecture documentation(Texas Tech University, 2001-08) Bagchi, SumantraHow can laser scanning technology be used to document a historical structure in such a way that the duration of the process is reduced and made less labor intensive, with the quality of documentation being equal to, or better than that required by the Historic American Buildings Survey (HABS), and that archival storage methods and accessibility to the public are enhanced? 3D Laser Scanning is a relatively new technique whereby pulses of light from a fixed source measure the exact co-ordinate position of points on a structure or object. This group or "cloud of points" accurately represents the object in three-dimensional virtual space. The application of 3D laser scanning technology to historic documentation in Texas Tech University was first examined in the measured drawing process of the JA Ranch, in Palo Duro Canyon, Texas. In this study, 1 described what eventuated and then analyzed a case study of this process with respect to time, labor, quality and image accessibility. This study had two steps. The first was to identify problems with the process that was followed, and the second was to suggest possible solutions in achieving an efficient procedure. The outcome of the case study analysis resulted in the delineation of an optimal course, which is replicable for a structure of comparable complexity.Item Topological consistency in skelatal modeling with convolution surfaces for conceptual design(2007-12) Ma, Guohua, 1970-; Crawford, Richard H.This dissertation describes a new topology analysis tool for a skeletal based geometric modeling system for conceptual design. Skeletal modeling is an approach to creating solid models in which the engineer designs with lower dimensional primitives such as points, lines, and triangles. The skeleton is then "skinned over" to create the surfaces of the three-dimensional object. In this research, convolution surfaces are used to provide the flesh to the skeleton. Convolution surfaces are generated by convolving a kernel function with a geometric field function to create an implicit surface. Certain properties of convolution surfaces make them attractive for skeletal modeling, including: (1) providing analytic solutions for various geometry primitives (including points, line segments, and triangles); (2) generating smooth surfaces; and (3) providing well-behaved blending. We assume that engineering designers expect the topology of a skeletal model to be identical to that of the underlying skeleton. However, the topology of convolution surfaces can change arbitrarily, making it difficult to predict the topology of the generated surface from knowledge of the topology of the skeleton. To address this issue, we apply Morse theory to analyze the topology of convolution surfaces by detecting the critical points of the surfaces. We developed an efficient and intelligent algorithm to find the critical points (CPs) by analyzing the skeleton. The critical points provide valuable information about the topology of the convolution surfaces. By tracking the CPs, we know where and what kind of topology changes happen when the threshold value reaches the critical value at the CP. Topology matching is done in two steps: (1) global topology is tested by comparing the Betti numbers (number of component, loops, and voids) of the skeleton and the generated convolution surfaces; (2) with matched Betti numbers, local topology is tested by comparing the location of each loop and void area between the skeleton and surfaces. If the topology does not match, appropriate heuristics for determining parameter values of the convolution surfaces are applied to force the surface topology to match that of the skeleton. A recommend threshold value is then provided to generate the topology matched convolution surfaces.Item Using complex light modulation for holographic applications(2016-05) Parthiban, Vikraman; Becker, Michael F.; Bovik, Alan CComplex light modulation is the ability to control a light-wave’s phase and amplitude, thereby allowing complete control of the light-wave at any spatial location. The applied optics group at The University of Texas at Austin Electrical and Computer Engineering Department created a fully complex hologram by a combination of spatial light modulators. A digital micromirror device (DMD) was used to produce a precise amplitude profile, and a liquid crystal spatial light modulator (SLM) was used to produce the phase profile. A band-limited 4-f imaging system imaged the DMD onto the SLM to create a fully complex modulated wavefront, which reconstructed a holographic image at the desired location. With this capability, it is possible to create improved imaging methods for the consumer, medical, and defense industries as well as applications in holography. Our previous research has successfully created phase-only holograms (POH), amplitude-only beam-shaping patterns, and published simulation results on full-complex modulation. This thesis provides an in-depth experimental analysis of the full-complex hologram.