Bernstein Polynomials for Radiative Transfer Computations

In this paper we propose using planar and spherical Bernstein polynomials over triangular domain for radiative transfer computations. In the planar domain, we propose using piecewise Bernstein basis functions and symmetric Gaussian quadrature formulas over triangular elements for high quality radiosity solution. In the spherical domain, we propose using piecewise Bernstein basis functions over a geodesic triangulation to represent the radiance function. The representation is intrinsic to the unit sphere, and may be efficiently stored, evaluated, and subdivided by the de Casteljau algorithm. The computation of other fundamental radiometric quantities such as vector irradiance and reflected radiance may be reduced to the integration of the piecewise Bernstein basis functions on the unit sphere. The key result of our work is a simple geometric integration algorithm based on adaptive domain subdivision for the Bernstein-Bézier polynomials over a geodesic triangle on the unit sphere

The reflectance and scattering of solar radiation by the earth

Spacecraft and balloon radiometry data, theories, and mathematical model of reflectance and scattering of solar radiation by eart

Computational Light Transport for Forward and Inverse Problems.

El transporte de luz computacional comprende todas las técnicas usadas para calcular el flujo de luz en una escena virtual. Su uso es ubicuo en distintas aplicaciones, desde entretenimiento y publicidad, hasta diseño de producto, ingeniería y arquitectura, incluyendo el generar datos validados para técnicas basadas en imagen por ordenador. Sin embargo, simular el transporte de luz de manera precisa es un proceso costoso. Como consecuencia, hay que establecer un balance entre la fidelidad de la simulación física y su coste computacional. Por ejemplo, es común asumir óptica geométrica o una velocidad de propagación de la luz infinita, o simplificar los modelos de reflectancia ignorando ciertos fenómenos. En esta tesis introducimos varias contribuciones a la simulación del transporte de luz, dirigidas tanto a mejorar la eficiencia del cálculo de la misma, como a expandir el rango de sus aplicaciones prácticas. Prestamos especial atención a remover la asunción de una velocidad de propagación infinita, generalizando el transporte de luz a su estado transitorio. Respecto a la mejora de eficiencia, presentamos un método para calcular el flujo de luz que incide directamente desde luminarias en un sistema de generación de imágenes por Monte Carlo, reduciendo significativamente la variancia de las imágenes resultantes usando el mismo tiempo de ejecución. Asimismo, introducimos una técnica basada en estimación de densidad en el estado transitorio, que permite reusar mejor las muestras temporales en un medio parcipativo. En el dominio de las aplicaciones, también introducimos dos nuevos usos del transporte de luz: Un modelo para simular un tipo especial de pigmentos gonicromáticos que exhiben apariencia perlescente, con el objetivo de proveer una forma de edición intuitiva para manufactura, y una técnica de imagen sin línea de visión directa usando información del tiempo de vuelo de la luz, construida sobre un modelo de propagación de la luz basado en ondas.<br /

Efficient Methods for Computational Light Transport

En esta tesis presentamos contribuciones sobre distintos retos computacionales relacionados con transporte de luz. Los algoritmos que utilizan información sobre el transporte de luz están presentes en muchas aplicaciones de hoy en día, desde la generación de efectos visuales, a la detección de objetos en tiempo real. La luz es una valiosa fuente de información que nos permite entender y representar nuestro entorno, pero obtener y procesar esta información presenta muchos desafíos debido a la complejidad de las interacciones entre la luz y la materia. Esta tesis aporta contribuciones en este tema desde dos puntos de vista diferentes: algoritmos en estado estacionario, en los que se asume que la velocidad de la luz es infinita; y algoritmos en estado transitorio, que tratan la luz no solo en el dominio espacial, sino también en el temporal. Nuestras contribuciones en algoritmos estacionarios abordan problemas tanto en renderizado offline como en tiempo real. Nos enfocamos en la reducción de varianza para métodos offline,proponiendo un nuevo método para renderizado eficiente de medios participativos. En renderizado en tiempo real, abordamos las limitacionesde consumo de batería en dispositivos móviles proponiendo un sistema de renderizado que incrementa la eficiencia energética en aplicaciones gráficas en tiempo real. En el transporte de luz transitorio, formalizamos la simulación de este tipo transporte en este nuevo dominio, y presentamos nuevos algoritmos y métodos para muestreo eficiente para render transitorio. Finalmente, demostramos la utilidad de generar datos en este dominio, presentando un nuevo método para corregir interferencia multi-caminos en camaras Timeof- Flight, un problema patológico en el procesamiento de imágenes transitorias.n this thesis we present contributions to different challenges of computational light transport. Light transport algorithms are present in many modern applications, from image generation for visual effects to real-time object detection. Light is a rich source of information that allows us to understand and represent our surroundings, but obtaining and processing this information presents many challenges due to its complex interactions with matter. This thesis provides advances in this subject from two different perspectives: steady-state algorithms, where the speed of light is assumed infinite, and transient-state algorithms, which deal with light as it travels not only through space but also time. Our steady-state contributions address problems in both offline and real-time rendering. We target variance reduction in offline rendering by proposing a new efficient method for participating media rendering. In real-time rendering, we target energy constraints of mobile devices by proposing a power-efficient rendering framework for real-time graphics applications. In transient-state we first formalize light transport simulation under this domain, and present new efficient sampling methods and algorithms for transient rendering. We finally demonstrate the potential of simulated data to correct multipath interference in Time-of-Flight cameras, one of the pathological problems in transient imaging.<br /

Towards Predictive Rendering in Virtual Reality

The strive for generating predictive images, i.e., images representing radiometrically correct renditions of reality, has been a longstanding problem in computer graphics. The exactness of such images is extremely important for Virtual Reality applications like Virtual Prototyping, where users need to make decisions impacting large investments based on the simulated images. Unfortunately, generation of predictive imagery is still an unsolved problem due to manifold reasons, especially if real-time restrictions apply. First, existing scenes used for rendering are not modeled accurately enough to create predictive images. Second, even with huge computational efforts existing rendering algorithms are not able to produce radiometrically correct images. Third, current display devices need to convert rendered images into some low-dimensional color space, which prohibits display of radiometrically correct images. Overcoming these limitations is the focus of current state-of-the-art research. This thesis also contributes to this task. First, it briefly introduces the necessary background and identifies the steps required for real-time predictive image generation. Then, existing techniques targeting these steps are presented and their limitations are pointed out. To solve some of the remaining problems, novel techniques are proposed. They cover various steps in the predictive image generation process, ranging from accurate scene modeling over efficient data representation to high-quality, real-time rendering. A special focus of this thesis lays on real-time generation of predictive images using bidirectional texture functions (BTFs), i.e., very accurate representations for spatially varying surface materials. The techniques proposed by this thesis enable efficient handling of BTFs by compressing the huge amount of data contained in this material representation, applying them to geometric surfaces using texture and BTF synthesis techniques, and rendering BTF covered objects in real-time. Further approaches proposed in this thesis target inclusion of real-time global illumination effects or more efficient rendering using novel level-of-detail representations for geometric objects. Finally, this thesis assesses the rendering quality achievable with BTF materials, indicating a significant increase in realism but also confirming the remainder of problems to be solved to achieve truly predictive image generation

Bayesian atmospheric retrieval for exoplanets : uniqueness of exoplanet spectra, characterizations of super-earths, and evaluations of dedicated space telescope designs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.This thesis was scanned as part of an electronic thesis pilot project.Cataloged from PDF version of thesis.Includes bibliographical references (p. 181-187).After centuries of studying the eight planets in our solar system, recent improvements in technology have given us the unprecedented opportunity to detect planets orbiting stars other than the sun, so-called exoplanets. Recent statistical studies based on 800 confirmed planets and more than 3000 planet candidates suggest that our galaxy is teeming with billions of planets. Many of them are likely to orbit their host stars at a distance where liquid water and potentially life can exist. Spectroscopic observations of exoplanets can provide us with information about the atmospheres and conditions on these distant worlds. This thesis presents a Bayesian retrieval framework to analyze spectroscopic observations of exoplanets to infer the planet's atmospheric compositions, the surface pressures, and the presences of clouds or hazes. I identify what can unambiguously be determined about the atmospheres of exoplanets by applying the retrieval method to sets of synthetic observations. The main finding is that a unique constraint of the atmospheric mixing ratios of all infrared absorbing gases and up to two spectrally inactive gases is possible if the spectral coverage of the observations is sufficient to (1) determine the broadband transit depths in at least one absorption feature for each absorbing gas and (2) measure the slope and strength of the molecular Rayleigh scattering signature. For the newly discovered class of low-density super-Earths, with radii and masses intermediate between Earth and Neptune, I present an observational approach to distinguish whether these planets more closely resemble the giant planets in our solar system or whether they represent a completely new, potentially water vapor-rich type of planet. The approach discussed in this work represents the science case for the largest Hubble Space Telescope program ever awarded for a single exoplanet. The numerical methods and the conceptual understanding of atmospheric spectra presented in this thesis are key for the design of future space telescopes dedicated to the characterization of transiting exoplanets. I present an integrated design evaluation framework for the proposed Exoplanet Characterization Observatory (EChO) that simultaneously models the astrophysical signal and the telescope's payload module. I demonstrate that costly cryogenic cooling to observe the mid-infrared spectrum beyond ~ 11 [mu]m is not required while visible light observations down to - 400 nm are essential for the mission success. The observational study of exoplanet atmospheres is in its infancy and its pace is poised to accelerate as observational techniques are improved and dedicated space missions are designed. The methods developed in this thesis will contribute to constraining the atmospheric properties of a wide variety of planets ranging from blazingly-hot gas giants to temperate Earth-like planets.by Björn Benneke.Ph.D

Simulación visual de materiales : teoría, técnicas, análisis de casos

Descripció del recurs: 29 de gener de 2016La simulación de materiales tiene una gran importancia, teórica y práctica, desde múltiples puntos de vista y aplicaciones profesionales. Es un requisito fundamental para la creación de escenarios virtuales y está imbricada en el propio proceso de diseño. Pues los colores, texturas, reflejos o transparencias, modifican las formas y espacios que percibimos. Las posibilidades que se han abierto a partir del desarrollo de nuevos recursos de interacción virtual, abren vías que solo desde hace pocos años estamos comenzando a asimilar. Este libro, que se publica en paralelo con otro sobre Simulación visual de la iluminación, abarca todo lo implicado en esta temática, tanto desde un punto de vista teórico y conceptual, a lo largo de su primera parte, como por medio de una explicación pormenorizada, a lo largo de su segunda parte, de las principales técnicas con que contamos en la actualidad, proporcionando ejemplos relevantes para diferentes aplicaciones, principalmente en arquitectura y diseño

Wavelength Dependent Reflectance Functions

Abstract A wavelength based bidirectional reflectance function is developedfor use in realistic image synthesis. A geodesic sphere is employed to represent the BRDF, and a novel data structure is used to storethis description and to recall it for rendering purposes. A virtual goniospectrophotometer is implemented by using a Monte Carloray tracer to cast rays into a surface. An optics model that incorporates phase is used in the ray tracer to simulate interference effects.An adaptive subdivision technique is applied to elaborate the data structure from rays scattered into the hemisphere above the surface.The wavelength based BRDF and virtual goniospectrophotometer are utilized to analyze and make pictures of thin films, idealizedpigmented materials, and pearlescent paints