Virtual light fields for global illumination in computer graphics

This thesis presents novel techniques for the generation and real-time rendering of globally illuminated environments with surfaces described by arbitrary materials. Real-time rendering of globally illuminated virtual environments has for a long time been an elusive goal. Many techniques have been developed which can compute still images with full global illumination and this is still an area of active flourishing research. Other techniques have only dealt with certain aspects of global illumination in order to speed up computation and thus rendering. These include radiosity, ray-tracing and hybrid methods. Radiosity due to its view independent nature can easily be rendered in real-time after pre-computing and storing the energy equilibrium. Ray-tracing however is view-dependent and requires substantial computational resources in order to run in real-time. Attempts at providing full global illumination at interactive rates include caching methods, fast rendering from photon maps, light fields, brute force ray-tracing and GPU accelerated methods. Currently, these methods either only apply to special cases, are incomplete exhibiting poor image quality and/or scale badly such that only modest scenes can be rendered in real-time with current hardware. The techniques developed in this thesis extend upon earlier research and provide a novel, comprehensive framework for storing global illumination in a data structure - the Virtual Light Field - that is suitable for real-time rendering. The techniques trade off rapid rendering for memory usage and precompute time. The main weaknesses of the VLF method are targeted in this thesis. It is the expensive pre-compute stage with best-case O(N^2) performance, where N is the number of faces, which make the light propagation unpractical for all but simple scenes. This is analysed and greatly superior alternatives are presented and evaluated in terms of efficiency and error. Several orders of magnitude improvement in computational efficiency is achieved over the original VLF method. A novel propagation algorithm running entirely on the Graphics Processing Unit (GPU) is presented. It is incremental in that it can resolve visibility along a set of parallel rays in O(N) time and can produce a virtual light field for a moderately complex scene (tens of thousands of faces), with complex illumination stored in millions of elements, in minutes and for simple scenes in seconds. It is approximate but gracefully converges to a correct solution; a linear increase in resolution results in a linear increase in computation time. Finally a GPU rendering technique is presented which can render from Virtual Light Fields at real-time frame rates in high resolution VR presentation devices such as the CAVETM

Técnicas de aceleración para el método de radiosidad jerárquica

[Resumen] Uno de los métodos que mejor modelan el comportamiento real de la luz en la búsqueda del realismo visual en imágenes construidas de forma sintética es el método de radiosidad. Este método presenta, sin embargo, el inconveniente de un alto coste computacional, tanto en tiempo de cálculo como en almacenamiento. Entre las numerosas variantes surgidas con el objetivo de rebajar la complejidad del método clásico destaca el método de radiosidad jerárquica, basado en la aplicación de una subdivisión adaptativa de la escena. El método de radiosidad jerárquica mantiene, no obstante, todavía una elevada complejidad que dificulta su explotación en escenas de gran tamaño. En este trabajo se han tratado de desarrollar nuevas soluciones para algunos de los diversos problemas que el método jerárquico de radiosidad plantea. El primer punto en el que se centra el trabajo es en la determinación de la visibilidad entre los distintos objetos de una escena (principal cuello de botella en un algoritmo de iluminación), analizando las principales soluciones existentes y proponiendo una nueva aproximación al problema, basada en aprovechar el principio de localidad en el espacio de direcciones de los rayos lanzados durante el proceso. Otro aspecto desarrollado en la tesis es la utilización de modelos geométricos de diferentes complejidades que permitan el tratamiento de escenas grandes con objetos detallados, independizando la correcta simulación de la distribución de la energía en la escena de la complejidad geométrica de los objetos que la componen. A este respecto se presenta una propuesta para el cálculo de la radiosidad jerárquica basada en el uso de esquemas de subdivisión de superficies. Por último, en esta tesis se propone una solución paralela para el aprovechamiento de sistemas distribuidos en la aplicación del método de radiosidad jerárquica en escenas de gran tamaño, realizando una distribución real de la geometría de la escena entre todas las memorias del sistema y con una aproximación multi-hilo para la ejecución, lo que va a permitir un mejor ajuste de la granularidad utilizada en la paralelización de las tareas.[Resumo] Uns dos métodos que mellor modelan o comportamento real da luz na búsqueda do realismo visual en imaxes construidas de forma sintética é o método de radiosidade. Este método presenta, sen embargo, a desvantaxe dun alto coste computacional, tanto en tempo de cálculo coma en almacenamento. Entre as numerosas variantes xurdidas co obxectivo de rebaixar a complexidade do método clásico sobresae o método de radiosidade xerárquica, baseado na aplicación dunha subdivisión adaptativa na escea. O método de radiosidade xerárquica mantén todavía, así a todo, unha elevada complexidade que dificulta a súa explotación en esceas de gran tamaño. Neste traballo tratáronse de desenvolver novas solucións para algúns dos diversos problemas plantexados polo método de radiosidade xerárquica. O primeiro punto ao que se presta atención no traballo é á determinación de visibilidade entre os distintos obxectos dunha escea (principal colo de botella nun algoritmo de iluminación), analizando as principais solucións existentes e propondo unha nova aproximación ao problema baseada no aproveitamento do principio de localidade no espazo de direccións dos raios lanzados durante o proceso. Outro aspecto desenvolvido na tese é a utilización de modelos xeométricos de diferente complexidad que permitan o tratamento de esceas grandes con obxectos moi detallados, independizando a correcta simulación da distribución da enerxía na escea da complexidade xeométrica dos obxectos que a compoñen. Ao respecto preséntase unha proposta para o cálculo da radiosidade xerárquica baseada no uso de esquemas de subdivisión de superficies. Por último, nesta tese proponse unha solución paralela para o aproveitamento de sistemas distribuidos na aplicación do método de radiosidade xerárquica en esceas de gran tamaño, facendo unha distribución real da xeometría da escea entre todas as memorias do sistema e cunha aproximación multi-fío na execución, o que vai permitir un mellor axuste da granularidade empregada na paralelización das tarefas.[Absract] Radiosity is one of the best methods in modelling the physical behaviour of light in a synthetic scene. However, the main drawback is the high requirements in terms of computational and storage costs. Hierarchical radiosity stands out among the different alternatives to reduce complexity in classic radiosity, applying an adaptive subdivision on scene. Hierarchical radiosity still presents, anyway, a high complexity that difficults to process really large scenes. In this work we have developed new solutions for several of the most common bottenecks presented in hierarchical radiosity. Our first goal is to accelerate visibility determination (most consuming task in global illumination), analysing the main existing solutions and proposing a new method based in taking advantage of directional coherence for the rays casted during process. Other aspect we have touched in the thesis is the use of multiresolution models that allow to work with very complex geometrical models in our input scene, isolating geometry detail and illumination detail. Specifically, we have developed a new method to compute hierarchical radiosity based on surface subdivision. Finally, a new parallel solution for computing hierarchical radiosity on multiprocessor systems, allowing huge input scenes is presented. The scene is totally distributed (geometrically and computationally) among the processors in our proposal, and a multi-thread implementation improves the flexibility in the granularity of the parallel execution

Numerical Geometric Acoustics

Sound propagation in air is accurately described by a small perturbation of the ambient pressure away from a quiescent state. This is the realm of linear acoustics, where the propagation of a time-harmonic wave can be modeled using the Helmholtz equation. When the wavelength is small relative to the size of a scattering obstacle, techniques from geometric optics are applicable. Geometric methods such as raytracing are often used for computational room acoustics simulations in situations where the geometry of the built environment is sufficiently complicated. At the same time, the high-frequency approximation of the Helmholtz equation is described by two partial differential equations: the eikonal equation, whose solution gives the first arrival time of a geometric acoustics/optics wavefront as a field; and a transport equation, the solution of which describes the amplitude of that wavefield. Phenomena related to high-frequency acoustic diffraction are frequently omitted from these models because of their complexity. These phenomena can be modeled using a high-frequency diffraction theory, such as the uniform theory of diffraction. Despite their shortcomings, geometric methods for room acoustics provide a useful trade-off between realism and computational efficiency. Motivated by the limitations of geometric methods, we approach the problem of geometric acoustics using numerical methods for solving partial differential equations. Our focus is offline sound propagation in a high-frequency regime where directly solving the wave or Helmholtz equations is infeasible. To this end, we conduct a broad-based survey of semi-Lagrangian solvers for the eikonal equation, which make the local ray information of the solution explicit. We develop efficient, first-order solvers for the eikonal equation in 3D, called ordered line integral methods (OLIMs). The OLIMs provide intuition about how to design work-efficient semi-Lagrangian eikonal solvers, but their first order accuracy is not sufficient to compute the amplitude consistently. Motivated by the requirements of sound propagation simulations, we develop higher-order semi-Lagrangian eikonal solvers which we term jet marching methods (JMMs). JMMs augment the efficiency of OLIMs by additionally transporting higher-order derivative information of the eikonal in a causal fashion, which allows for high-order solution of the eikonal equation using compact stencils. We use the information made available locally by our JMMs to use paraxial raytracing to simultaneously solve the transport equation yielding the amplitude. We initially develop a JMM which handles a smoothly varying speed of sound on a regular grid in 2D. Motivated by the requirements of room acoustics applications, we develop a second-order JMM for solving the eikonal equation on a tetrahedron mesh for a constant speed of sound as a special case. As before, we use paraxial raytracing to compute the amplitude. Additionally, we compute multiple arrivals by reinitializing the eikonal equation on reflecting walls and diffracting edges. To compute these scattered fields, we devise algorithms which allow us to apply reflection and diffraction boundary conditions for the eikonal and amplitude. For the amplitude, we construct algorithms that allow us to apply the uniform theory of diffraction in a semi-Lagrangian setting efficiently

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 /

Voyager spacecraft system. Volume B - Alternate designs considered for flight spacecraft and hardware subsystems Final technical report

Alternate mission objectives, design characteristics, and system and subsystem designs for Voyager spacecraft syste

A Flexible, Low-Power, Programmable Unsupervised Neural Network Based on Microcontrollers for Medical Applications

We present an implementation and laboratory tests of a winner takes all (WTA) artificial neural network (NN) on two microcontrollers (μC) with the ARM Cortex M3 and the AVR cores. The prospective application of this device is in wireless body sensor network (WBSN) in an on-line analysis of electrocardiograph (ECG) and electromyograph (EMG) biomedical signals. The proposed device will be used as a base station in the WBSN, acquiring and analysing the signals from the sensors placed on the human body. The proposed system is equiped with an analog-todigital converter (ADC), and allows for multi-channel acquisition of analog signals, preprocessing (filtering) and further analysis