A parametric-space-based scan-line algorithm for rendering of bicubic surfaces

A novel scan-line algorithm for displaying bicubic surfaces is presented. Patches are decomposed on regions of constant sign of the z component of the normal before the scan process. Most of the computations are done in parametric space. The algorithm computes the intersection of the surfaces with only a restricted subset of scan planes and obtains the intersection with other scan planes by linear interpolation between exact intersections. A bound of the algorithm's error is given. The method is compared with Whitted's algorithm.Postprint (published version

Hidden curve removal for free form surfaces

Journal ArticleThis paper describes a hidden curve algorithm specifically designed for sculptured surfaces. A technique is described to extract the visible curves for a given scene without the need to approximate the surface by polygons. This algorithm produces higher quality results than polygon based algorithms, as most of the output set has an exact representation. Surface coherence is used to speed up the process. Although designed for sculptured surfaces, this algorithm is also suitable for polygonal data

Scientific visualization of stress tensor information with applications to stress determination by X-ray and neutron diffraction

Includes bibliographical references (leaves 232-249).The visual analysis of mechanical stress facilitates physical understanding of the tensor quantity which is concealed in scalar and vector methods. In this study, the principles and techniques of scientific visualization are used to develop a visual analysis of mechanical stresses. Scientific visualization is not only applied to the final tensorial quantity obtained from the diffraction measurements, but the visual methods are developed from, and integrated into current residual stress analysis practices by relating the newly developed visual techniques to the conventional techniques, highlighting its advantages. This study consists of the mathematical analysis of the tensor character of mechanical stresses, discussion of the principles and techniques of scientific visualization (visual data analysis) in physical research, and tensor determination, visual analysis and presentation of residual stresses obtained from diffraction measurements

Computer-Aided Geometry Modeling

Techniques in computer-aided geometry modeling and their application are addressed. Mathematical modeling, solid geometry models, management of geometric data, development of geometry standards, and interactive and graphic procedures are discussed. The applications include aeronautical and aerospace structures design, fluid flow modeling, and gas turbine design

Electromagnetic analysis of bidirectional reflectance from roughened surfaces and applications to surface shape recovery

Scattering from randomly rough surfaces is a well-established sub area of electrodynamics. There remains much to be done since each surface and optical processes that may occur in within the scattering medium, and countless other scenarios, is different. There are also illumination models that describe lighting in a scene on the macroscopic scale where geometrical optics can be considered adequate. Of particular interest for us is the intersection of the physical scattering theories and the illumination models. We present two contributions: 1) A minimum of two independent images are needed since any opaque surface can be uniquely specified in terms of its outward-normal vector field. This required the development of a global, nonlinear, alternating optimization scheme to compute parameter estimates. It is shown that high accuracy estimates can be obtained. 2)The smooth emergence of geometrical optics from physical optics using a full wave electromagnetic solution of the 1D scattering problem. It is shown here that the geometrical optics limit is arrived at in a smooth transition from physical optics starting with the electric field integral equation by varying the size of roughness structures on the surface and calculating the scattering cross length . Starting from roughness features smaller than the incident wavelength and also considering the size of the surface fluctuations relative to the size of the surface, the scattered light patterns show expected wave behavior that gradually transitions to geometrical ray optics as the size of surface roughness features increases well beyond the wavelength

Doctor of Philosophy

dissertationThe result of this dissertation enables routine calculation for removal of vehiclegenerated particulate matter with a mean aerodynamic diameter less than 10 microns (known as PM10) downwind of unpaved roads given the height and density of vegetation downwind of the road. At present, the calculation of PM10 removal given vegetative height and density requires an expensive field study or classifying the vegetation as being one of five very general vegetative types. The estimation of PM10 removal downwind of an unpaved road is important in developing net PM10 emission inventories for use in regional air-quality models. Current methodologies for estimating PM10 removal by downwind roughness elements are based on the results of a small number of field studies measuring removal under limited roughness and atmospheric conditions. To significantly increase the data relating PM10 removal rate to site roughness and atmospheric stability, numerical modeling is employed and an additional field study is performed. The simulations utilize Lagrangian dispersion and Atmospheric Diffusion Equation (ADE) techniques. The new field study site features roughness and meteorological conditions distinct from those previously documented in the existing peer-reviewed literature. The PM10 removal measured in the field studies compared well, within a relative 10% error, to the numerical simulation predictions of PM10 removal for the field study site conditions. The simulation results indicate that PM10 removal is related to roughness and atmospheric stability by: ( 1 - CF) = ( 1 - exp( - 2 . 8H*)) exp( - 2 . 0 T**0■ 64) + exp( - 2 . 8H*), where CF is the captured fraction of PMio within the first 100 m and H * and T* parameterize site roughness and meteorological conditions. Qualitatively, this equation indicates that CF increases with atmospheric stability, canopy height, and canopy density. Simple transport models for mean horizontal advection and vertical turbulence within downwind roughness are developed for use in numerical simulations. The models are applicable for both canopies (an array of horizontally homogeneous roughness elements with infinite fetch) and windbreaks (an array of nonhorizontally homogeneous roughness elements located in rows with finite fetches). These transport models have simple inputs, such as vegetative mean height, leaf area index (for canopies), and optical porosity (for windbreaks). These models are also applicable for all practical atmospheric stabilities, roughness heights, and most roughness densities (canopies with frontal area indexes greater than 0.075 and windbreaks with optical porosities less than 0.9). For sparsely distributed roughness elements, traditional atmospheric surface layer parameterizations are more appropriate

Efficient and High-Quality Rendering of Higher-Order Geometric Data Representations

Computer-Aided Design (CAD) bezeichnet den Entwurf industrieller Produkte mit Hilfe von virtuellen 3D Modellen. Ein CAD-Modell besteht aus parametrischen Kurven und Flächen, in den meisten Fällen non-uniform rational B-Splines (NURBS). Diese mathematische Beschreibung wird ebenfalls zur Analyse, Optimierung und Präsentation des Modells verwendet. In jeder dieser Entwicklungsphasen wird eine unterschiedliche visuelle Darstellung benötigt, um den entsprechenden Nutzern ein geeignetes Feedback zu geben. Designer bevorzugen beispielsweise illustrative oder realistische Darstellungen, Ingenieure benötigen eine verständliche Visualisierung der Simulationsergebnisse, während eine immersive 3D Darstellung bei einer Benutzbarkeitsanalyse oder der Designauswahl hilfreich sein kann. Die interaktive Darstellung von NURBS-Modellen und -Simulationsdaten ist jedoch aufgrund des hohen Rechenaufwandes und der eingeschränkten Hardwareunterstützung eine große Herausforderung. Diese Arbeit stellt vier neuartige Verfahren vor, welche sich mit der interaktiven Darstellung von NURBS-Modellen und Simulationensdaten befassen. Die vorgestellten Algorithmen nutzen neue Fähigkeiten aktueller Grafikkarten aus, um den Stand der Technik bezüglich Qualität, Effizienz und Darstellungsgeschwindigkeit zu verbessern. Zwei dieser Verfahren befassen sich mit der direkten Darstellung der parametrischen Beschreibung ohne Approximationen oder zeitaufwändige Vorberechnungen. Die dabei vorgestellten Datenstrukturen und Algorithmen ermöglichen die effiziente Unterteilung, Klassifizierung, Tessellierung und Darstellung getrimmter NURBS-Flächen und einen interaktiven Ray-Casting-Algorithmus für die Isoflächenvisualisierung von NURBSbasierten isogeometrischen Analysen. Die weiteren zwei Verfahren beschreiben zum einen das vielseitige Konzept der programmierbaren Transparenz für illustrative und verständliche Visualisierungen tiefenkomplexer CAD-Modelle und zum anderen eine neue hybride Methode zur Reprojektion halbtransparenter und undurchsichtiger Bildinformation für die Beschleunigung der Erzeugung von stereoskopischen Bildpaaren. Die beiden letztgenannten Ansätze basieren auf rasterisierter Geometrie und sind somit ebenfalls für normale Dreiecksmodelle anwendbar, wodurch die Arbeiten auch einen wichtigen Beitrag in den Bereichen der Computergrafik und der virtuellen Realität darstellen. Die Auswertung der Arbeit wurde mit großen, realen NURBS-Datensätzen durchgeführt. Die Resultate zeigen, dass die direkte Darstellung auf Grundlage der parametrischen Beschreibung mit interaktiven Bildwiederholraten und in subpixelgenauer Qualität möglich ist. Die Einführung programmierbarer Transparenz ermöglicht zudem die Umsetzung kollaborativer 3D Interaktionstechniken für die Exploration der Modelle in virtuellenUmgebungen sowie illustrative und verständliche Visualisierungen tiefenkomplexer CAD-Modelle. Die Erzeugung stereoskopischer Bildpaare für die interaktive Visualisierung auf 3D Displays konnte beschleunigt werden. Diese messbare Verbesserung wurde zudem im Rahmen einer Nutzerstudie als wahrnehmbar und vorteilhaft befunden.In computer-aided design (CAD), industrial products are designed using a virtual 3D model. A CAD model typically consists of curves and surfaces in a parametric representation, in most cases, non-uniform rational B-splines (NURBS). The same representation is also used for the analysis, optimization and presentation of the model. In each phase of this process, different visualizations are required to provide an appropriate user feedback. Designers work with illustrative and realistic renderings, engineers need a comprehensible visualization of the simulation results, and usability studies or product presentations benefit from using a 3D display. However, the interactive visualization of NURBS models and corresponding physical simulations is a challenging task because of the computational complexity and the limited graphics hardware support. This thesis proposes four novel rendering approaches that improve the interactive visualization of CAD models and their analysis. The presented algorithms exploit latest graphics hardware capabilities to advance the state-of-the-art in terms of quality, efficiency and performance. In particular, two approaches describe the direct rendering of the parametric representation without precomputed approximations and timeconsuming pre-processing steps. New data structures and algorithms are presented for the efficient partition, classification, tessellation, and rendering of trimmed NURBS surfaces as well as the first direct isosurface ray-casting approach for NURBS-based isogeometric analysis. The other two approaches introduce the versatile concept of programmable order-independent semi-transparency for the illustrative and comprehensible visualization of depth-complex CAD models, and a novel method for the hybrid reprojection of opaque and semi-transparent image information to accelerate stereoscopic rendering. Both approaches are also applicable to standard polygonal geometry which contributes to the computer graphics and virtual reality research communities. The evaluation is based on real-world NURBS-based models and simulation data. The results show that rendering can be performed directly on the underlying parametric representation with interactive frame rates and subpixel-precise image results. The computational costs of additional visualization effects, such as semi-transparency and stereoscopic rendering, are reduced to maintain interactive frame rates. The benefit of this performance gain was confirmed by quantitative measurements and a pilot user study

Material-based design computation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 306-328).The institutionalized separation between form, structure and material, deeply embedded in modernist design theory, paralleled by a methodological partitioning between modeling, analysis and fabrication, resulted in geometric-driven form generation. Such prioritization of form over material was carried into the development and design logic of CAD. Today, under the imperatives and growing recognition of the failures and environmental liabilities of this approach, modern design culture is experiencing a shift to material aware design. Inspired by Nature's strategies where form generation is driven by maximal performance with minimal resources through local material property variation, the research reviews, proposes and develops models and processes for a material-based approach in computationally enabled form-generation. Material-based Design Computation is developed and proposed as a set of computational strategies supporting the integration of form, material and structure by incorporating physical form-finding strategies with digital analysis and fabrication. In this approach, material precedes shape, and it is the structuring of material properties as a function of structural and environmental performance that generates design form. The thesis proposes a unique approach to computationally-enabled form-finding procedures, and experimentally investigates how such processes contribute to novel ways of creating, distributing and depositing material forms. Variable Property Design is investigated as a theoretical and technical framework by which to model, analyze and fabricate objects with graduated properties designed to correspond to multiple and continuously varied functional constraints. The following methods were developed as the enabling mechanisms of Material Computation: Tiling Behavior & Digital Anisotropy, Finite Element Synthesis, and Material Pixels. In order to implement this approach as a fabrication process, a novel fabrication technology, termed Variable Property Rapid Prototyping has been developed, designed and patented. Among the potential contributions is the achievement of a high degree of customization through material heterogeneity as compared to conventional design of components and assemblies. Experimental designs employing suggested theoretical and technical frameworks, methods and techniques are presented, discussed and demonstrated. They support product customization, rapid augmentation and variable property fabrication. Developed as approximations of natural formation processes, these design experiments demonstrate the contribution and the potential future of a new design and research field.by Neri Oxman.Ph.D

Abstracts of Papers, 85th Annual Meeting of the Virginia Academy of Science, May 24-26, 2007, James Madison University, Harrisonburg VA

Full abstracts of the 85th Annual Meeting of the Virginia Academy of Science, May 24-26, 2007, James Madison University, Harrisonburg V

Aeronautical Engineering: A special bibliography with indexes, supplement 54

This bibliography lists 316 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1975