Browsing by Subject "Three-dimensional display systems"
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Item Boundary/finite element meshing from volumetric data with applications(2005) Zhang, Yongjie; Bajaj, ChandrajitThe main research work during my Ph.D. study is to extract adaptive and quality 2D (triangular or quadrilateral) meshes over isosurfaces and 3D (tetrahedral or hexahedral) meshes with isosurfaces as boundaries directly from volumetric imaging data. The software named LBIE-Mesher (Level Set Boundary Interior and Exterior Mesher) is developed. LBIE-Mesher generates 3D meshes for the volume interior to an isosurface, the volume exterior to an isosurface, or the interval volume between two isosurfaces. An algorithm has been developed to extract adaptive and quality 3D meshes directly from volumetric imaging data. The extracted tetrahedral meshes are extensively used in the Finite Element Method (FEM). A top-down octree subdivision coupled with the dual contouring method is used to rapidly extract adaptive 3D finite element meshes with correct topology from volumetric imaging data. The edge contraction and smoothing methods are used to improve the mesh quality. The main contribution is extending the dual contouring method to crack-free interval volume 3D meshing with feature sensitive adaptation. Compared to other tetrahedral extraction methods from imaging data, our method generates adaptive and quality 3D meshes without introducing any hanging nodes. Furthermore, another algorithm has been developed to extract adaptive and quality quadrilateral or hexahedral meshes directly from volumetric data. First, a bottom-up surface topology preserving octree-based algorithm is applied to select a starting octree level. Then the dual contouring method is used to extract a preliminary uniform quad/hex mesh, which is decomposed into finer quads/hexes adaptively without introducing any hanging nodes. The positions of all boundary vertices are recalculated to approximate the boundary surface more accurately. Mesh adaptivity can be controlled by a feature sensitive error function, the regions that users are interested in, or finite element calculation results. Finally, a relaxation based technique is deployed to improve mesh quality. Several demonstration examples are provided from a wide variety of application domains. An approach has been described to smooth the surface and improve the quality of surface/volume meshes with feature preserved using geometric flow. For triangular and quadrilateral surface meshes, the surface diffusion flow is selected to remove noise by relocating vertices in the normal direction, and the aspect ratio is improved with feature preserved by adjusting vertex positions in the tangent direction. For tetrahedral and hexahedral volume meshes, besides the surface vertex movement in the normal and tangent directions, interior vertices are relocated to improve the aspect ratio. Our method has the properties of noise removal, feature preservation and quality improvement of surface/volume meshes, and it is especially suitable for biomolecular meshes because the surface diffusion flow preserves sphere accurately if the initial surface is close to a sphere. A comprehensive approach has been proposed to construct quality meshes for imviii plicit solvation models of biomolecular structures starting from atomic resolution data in the Protein Data Bank (PDB). First, a smooth volumetric synthetic electron density map is constructed from parsed atomic location data of biomolecules in the PDB, using Gaussian isotropic kernels. An appropriate parameter selection is made for constructing an error bounded implicit solvation surface approximation to the Lee-Richards molecular surface. Next, a modified dual contouring method is used to extract triangular meshes for the molecular surface, and tetrahedral meshes for the volume inside or outside the molecule within a bounding sphere/box of influence. Finally, geometric flows are used to improve the mesh quality. Some of our generated meshes have been successfully used in finite element simulations. Techniques have been developed to generate an adaptive and quality tetrahedral finite element mesh of a human heart. An educational model and a patient-specific model are constructed. There are three main steps in our mesh generation: model acquisition, mesh extraction and boundary/material layer detection. (1) Model acquisition. Beginning from an educational polygonal model, we edit and convert it to volumetric gridded data. A component index for each cell edge and grid point is computed to assist the boundary and material layer detection. For the patient-specific model, some boundary points are selected from MRI images, and connected using cubic splines and lofting to segment the MRI data. Different components are identified. (2) Mesh extraction. We extract adaptive and quality tetrahedral meshes from the volumetric gridded data using our LBIE-Mesher. The mesh adaptivity is controlled by regions or using a feature sensitive error function. (3) Boundary/material layer detection. The boundary of each component and multiple material layers are identified and meshed. The extracted tetrahedral mesh of the educational model is being utilized in the analysis of cardiac fluid dynamics via immersed continuum method, and the generated patient-specific model will be used in simulating the electrical activity of the heart.Item Evaluation of an automated three-dimensional compensation algorithm for visual-display misalignment and effects of display formats in three-dimensional telerobor manipulation(Texas Tech University, 2000-08) Myung, SeonwanIn teleoperation environments, decision-making can be performed by a combination of knowledge-based autonomous procedures, sensor-based autonomous procedures, and/or the human operator. Humans can easily adapt to unpredictability in task environments, due to their superior problem solving skills and perceptual abilities. Therefore, using a human operator to make decisions is beneficial to the manual control of telerobot in real environments. When a robot is manually controlled in teleoperation, the control input of the operator is transmitted to the robot, and video cameras send visual feedback of the state of the robot to the operator. In this manner, the operator is engaged in the dynamic control of the robot. Some characteristics of this control have disadvantages. The visual feedback of remote manipulation by the video cameras requires a very high communication bandwidth to transmit the video signal. A small communication delay in control feedback deteriorates the teleoperation performance of the operator. The other disadvantage is due to spatial perturbations including depth problems and visual-display incompatibilities. Those perturbations can be reduced by training operators or using graphical aids. However, it usually takes a long time to get satisfying results through training, and most of the time it is very hard for operators to reach a satisfactory level of performance. The teleoperation visual system needs to provide sufficient visual information to allow various tasks to be accomplished. Understanding the relationship of the manipulator to some fixed reference plane is the basis for spatial orientation, and displaying control disorientation can result in degradation of operator performance as well as damage or loss of the manipulator. When multiple cameras or dynamically moving cameras are used in a manual operation, depending on the camera view angle, the axes of the manipulator are not aligned with the controller axes. This misalignment causes display-control incompatibility. Under the incompatibility conditions, the performance of the operator might be lower than the performance in compatibility conditions. In this research, 3-D automatic compensation method for visual-display compatibility was tested to reduce visual-display incompatibilities. Three different display formats with the 3-D compensation method were tested in telerobotic tracking simulation environments. The 3-D automatic compensation method can be applied to the display-control incompatibility conditions to reduce incompatibility. There is no need to change hardware settings for integrating the 3-D compensation method. In experiment I, the 3-D compensation method was integrated with the single display format. In experiment E, the 3-D compensation method was integrated with the three display formats and a visual mode. When the compensation method was used, performance was superior to the performance conditions in which the compensation method was not used. In addition, the single monitor with the 3-D compensation method saves cost by using a monitor and a low speed network connection as compared to using the multiple monitors. In each view, the operator works under display-control compatibility conditions, so that the operator freely select a good view without considering the display-control compatibility.Item Feasibility of applying small particle in-line holography to determine 3-D velocity fields within automobile engine compartments(Texas Tech University, 1989-08) Rippee, Michael PaulThis thesis presents an investigation into the feasibility of using particle field holography to determine air flow velocities typical of those within an automobile engine compartment. Three primary objectives are considered in this study. The first objective is to investigate the behavior of spherical microparticles of different sizes in order to determine a suitable particle size that would accurately represent local air velocities and could be resolved holographically. The second objective is to determine the velocity error due to the fluid acceleration to allow estimates of how well a given particle will represent the air flow. The third objective is to investigate the theoretical aspects of in-line particle field holography and to estimate particle velocity measurement errors. Particle velocity behavior is investigated by developing a computer program determine particle trajectories in an inviscid air stream flowing past a cylinder. The program predicted velocity errors and total accelerations. It was found that a 5-micron diameter water droplet could tolerate accelerations up to 900m/s^2 and still represent the air flow with an error of less than 1.5 percent. A theoretical investigation of in-line holography and experimental results from the literature indicates that a particle of 5 microns can be imaged throughout a sample volume of about 2.5 to 5 cm''. The longitudinal focal tolerance is the largest source of error when determining particle displacements. However, this error can be reduced if the longitudinal measurement is repeated several times. If three longitudinal measurements are made at each particle location, and if the particle travels 1 mm and the fluid acceleration is within the allowable limit for the particle size, then the local air velocity can be measured with an error of about 1.4 percent. Two serious disadvantages of using particle field holography to measure fluid velocities are the high equipment costs and the time required to analyze holograms. The construction of a low cost miniature ruby laser to experimentally verify air flow measurements is suggested.Item Fusion of depth and intensity data for three-dimensional object representation and recognition(Texas Tech University, 1991-12) Ramirez Cortes, Juan ManuelFor humans, retinal images provide sufficient information for the complete understanding of three-dimensional (3-D) shapes in a scene. The ultimate goal of computer vision is to develop an automated system able to reproduce some of the tasks performed in a natural way by human beings as recognition, classification, or analysis of the environment as basis for further decisions. At the first level, referred to as early computer vision, the task is to extract symbolic descriptive information in a scene from a variety of sensory data. The second level is concerned with classification, recognition, or decision systems and the related heuristics, that aid the processing of the available information. This research is concerned with a new approach to 3-D object representation and recognition using an interpolation scheme applied to the information from the fusion of range and intensity data. The range image acquisition uses a methodology based on a passive stereo-vision model originally developed to be used with a sequence of images.^^ However, curved features, large disparities and noisy input images are some of the problems associated with real imagery, which need to be addressed prior to applying the matching techniques in the spatial frequency domain. Some of the above mentioned problems can only be solved by computationally intensive spatial domain algorithms. Regularization techniques are explored for surface recovery from sparse range data, and intensity images are incorporated in the final representation of the surface. As an important application, the problem of 3-D representation of retinal images for extraction of quantitative information is addressed. Range information is also combined with intensity data to provide a more accurate numerical description based on aspect graphs. This representation is used as input to a three-dimensional object recognition system. Such an approach results in an improved performance of 3-D object classifiers.Item Virtual body structure: a three-dimensional tool(Texas Tech University, 2000-05) Stephens, Bryan HoytUnderstanding of the visuospatial aspects of anatomic stmctures is one of the most important goals of gross anatomy. Generation of realistic three-dimensional structures of human anatomy has thus been a dream of medical doctors and computer scientists. In this paper, we describe a PC-based system in which a user can select any anatomical structure, create its three-dimensional model, and then visualize and manipulate it as needed. We use segmented and classified Visible Human Male data and an advanced, open-architecture, graphics package to implement the system. The package makes it possible to quickly develop an integrated, scalable, environment while working at a higher level than the standard OpenGL techniques. The texture-mapping and animation features of the system allow visualization of the three-dimensional model(s) being built, providing a fundamental learning experience of 'building virtual body structure" in the mind. The system is currently being adapted to serve in a next generation Internet educational system for anatomy and surgery, helping to provide a validation of the use of computer graphics in the computer-assisted medical training.