Hardware accelerated computer graphics algorithms

The advent of shaders in the latest generations of graphics hardware, which has made consumer level graphics hardware partially programmable, makes now an ideal time to investigate new graphical techniques and algorithms as well as attempting to improve upon existing ones. This work looks at areas of current interest within the graphics community such as Texture Filtering, Bump Mapping and Depth of Field simulation. These are all areas which have enjoyed much interest over the history of computer graphics but which provide a great deal of scope for further investigation in the light of recent hardware advances. A new hardware implementation of a texture filtering technique, aimed at consumer level hardware, is presented. This novel technique utilises Fourier space image filtering to reduce aliasing. Investigation shows that the technique provides reduced levels of aliasing along with comparable levels of detail to currently popular techniques. This adds to the community's knowledge by expanding the range of techniques available, as well as increasing the number of techniques which offer the potential for easy integration with current consumer level graphics hardware along with real-time performance. Bump mapping is a long-standing and well understood technique. Variations and extensions of it have been popular in real-time 3D computer graphics for many years. A new hardware implementation of a technique termed Super Bump Mapping (SBM) is introduced. Expanding on the work of Cant and Langensiepen [1], the SBM technique adopts the novel approach of using normal maps which supply multiple vectors per texel. This allows the retention of much more detail and overcomes some of the aliasing deficiencies of standard bump mapping caused by the standard single vector approach and the non-linearity of the bump mapping process. A novel depth of field algorithm is proposed, which is an extension of the authors previous work [2][3][4]. The technique is aimed at consumer level hardware and attempts to raise the bar for realism by providing support for the 'see-through' effect. This effect is a vital factor in the realistic appearance of simulated depth of field and has been overlooked in real time computer graphics due to the complexities of an accurate calculation. The implementation of this new algorithm on current consumer level hardware is investigated and it is concluded that while current hardware is not yet capable enough, future iterations will provide the necessary functional and performance increases

Enhancing Mesh Deformation Realism: Dynamic Mesostructure Detailing and Procedural Microstructure Synthesis

Propomos uma solução para gerar dados de mapas de relevo dinâmicos para simular deformações em superfícies macias, com foco na pele humana. A solução incorpora a simulação de rugas ao nível mesoestrutural e utiliza texturas procedurais para adicionar detalhes de microestrutura estáticos. Oferece flexibilidade além da pele humana, permitindo a geração de padrões que imitam deformações em outros materiais macios, como couro, durante a animação. As soluções existentes para simular rugas e pistas de deformação frequentemente dependem de hardware especializado, que é dispendioso e de difícil acesso. Além disso, depender exclusivamente de dados capturados limita a direção artística e dificulta a adaptação a mudanças. Em contraste, a solução proposta permite a síntese dinâmica de texturas que se adaptam às deformações subjacentes da malha de forma fisicamente plausível. Vários métodos foram explorados para sintetizar rugas diretamente na geometria, mas sofrem de limitações como auto-interseções e maiores requisitos de armazenamento. A intervenção manual de artistas na criação de mapas de rugas e mapas de tensão permite controle, mas pode ser limitada em deformações complexas ou onde maior realismo seja necessário. O nosso trabalho destaca o potencial dos métodos procedimentais para aprimorar a geração de padrões de deformação dinâmica, incluindo rugas, com maior controle criativo e sem depender de dados capturados. A incorporação de padrões procedimentais estáticos melhora o realismo, e a abordagem pode ser estendida além da pele para outros materiais macios.We propose a solution for generating dynamic heightmap data to simulate deformations for soft surfaces, with a focus on human skin. The solution incorporates mesostructure-level wrinkles and utilizes procedural textures to add static microstructure details. It offers flexibility beyond human skin, enabling the generation of patterns mimicking deformations in other soft materials, such as leater, during animation. Existing solutions for simulating wrinkles and deformation cues often rely on specialized hardware, which is costly and not easily accessible. Moreover, relying solely on captured data limits artistic direction and hinders adaptability to changes. In contrast, our proposed solution provides dynamic texture synthesis that adapts to underlying mesh deformations. Various methods have been explored to synthesize wrinkles directly to the geometry, but they suffer from limitations such as self-intersections and increased storage requirements. Manual intervention by artists using wrinkle maps and tension maps provides control but may be limited to the physics-based simulations. Our research presents the potential of procedural methods to enhance the generation of dynamic deformation patterns, including wrinkles, with greater creative control and without reliance on captured data. Incorporating static procedural patterns improves realism, and the approach can be extended to other soft-materials beyond skin

Einstein equations in the null quasi-spherical gauge III: numerical algorithms

We describe numerical techniques used in the construction of our 4th order evolution for the full Einstein equations, and assess the accuracy of representative solutions. The code is based on a null gauge with a quasi-spherical radial coordinate, and simulates the interaction of a single black hole with gravitational radiation. Techniques used include spherical harmonic representations, convolution spline interpolation and filtering, and an RK4 "method of lines" evolution. For sample initial data of "intermediate" size (gravitational field with 19% of the black hole mass), the code is accurate to 1 part in 10^5, until null time z=55 when the coordinate condition breaks down.Comment: Latex, 38 pages, 29 figures (360Kb compressed

A journey in a procedural volume Optimization and filtering of Perlin noise

National audiencePerlin noise is the most widely used tool in procedural texture synthesis. It is a simple and fast method to enhance the quantity of detail or to render natural materials with no use of storage resources. However, this technique is very sensitive to aliasing artifacts, especially when composed with shape and color functions. Moreover, it is computationally intensive and can become slow, especially when generating procedural volumes of density in real time. This study aims at analyzing Perlin noise properties in order to control the apparition of artifacts and optimize the computational cost. We present a method for computing a maximum and minimum frequency threshold per noise component, we propose an idea to handle the case of non linear transforms of the noise, and show an optimization method for volume generation

Asteroseismology of 20,000 Kepler Red Giants

Asteroseismology is the study of stellar pulsations. Over the past decade, asteroseismology, in particular, the study of the solar-like oscillations, has entered its golden age and has caught attention across various fields, including exoplanet science and Galactic archaeology. With high-quality data from the CoRoT, Kepler, and TESS space missions, asteroseismology has been demonstrated to be an essential tool to characterise stars and probe stellar internal structure. In this thesis, I apply asteroseismic analyses to Kepler red giants showing a rich spectrum of solar-like oscillations, which are stochastically excited and intrinsically damped by surface turbulence. First of all, I give a brief introduction to some critical phases of stellar evolution and the fundamentals of asteroseismology. Then, I present in Chapter 2 the results on asteroseismology of 1523 red giants that were misclassified by the Kepler Input Catalog. A dedicated method was used to successfully discriminate for each star the real oscillation power excess from its alias. In Chapter 3, I present a catalog of global seismic parameters, masses, and radii for 16,000 red giants, which has been the largest and most homogeneous catalog. The results showed that oscillation amplitude and granulation power depend on mass and metallicity. Next, I show in Chapter 4 the results on asteroseismology of Long Period Variables (LPVs), which has provided strong evidence to address three long-standing open questions in LPVs. Oscillations and granulation are very valuable signals to characterise stars, but they introduce challenges to confirm and characterise small transiting exoplanets using radial velocity (RV) measurements. Chapter 5 shows predictions of RV jitter induced by oscillations and granulation for dwarfs and giants in terms of stellar parameters. The conclusions and some suggestions for future work are given in Chapter 6

Improved Encoding for Compressed Textures

For the past few decades, graphics hardware has supported mapping a two dimensional image, or texture, onto a three dimensional surface to add detail during rendering. The complexity of modern applications using interactive graphics hardware have created an explosion of the amount of data needed to represent these images. In order to alleviate the amount of memory required to store and transmit textures, graphics hardware manufacturers have introduced hardware decompression units into the texturing pipeline. Textures may now be stored as compressed in memory and decoded at run-time in order to access the pixel data. In order to encode images to be used with these hardware features, many compression algorithms are run offline as a preprocessing step, often times the most time-consuming step in the asset preparation pipeline. This research presents several techniques to quickly serve compressed texture data. With the goal of interactive compression rates while maintaining compression quality, three algorithms are presented in the class of endpoint compression formats. The first uses intensity dilation to estimate compression parameters for low-frequency signal-modulated compressed textures and offers up to a 3X improvement in compression speed. The second, FasTC, shows that by estimating the final compression parameters, partition-based formats can choose an approximate partitioning and offer orders of magnitude faster encoding speed. The third, SegTC, shows additional improvement over selecting a partitioning by using a global segmentation to find the boundaries between image features. This segmentation offers an additional 2X improvement over FasTC while maintaining similar compressed quality. Also presented is a case study in using texture compression to benefit two dimensional concave path rendering. Compressing pixel coverage textures used for compositing yields both an increase in rendering speed and a decrease in storage overhead. Additionally an algorithm is presented that uses a single layer of indirection to adaptively select the block size compressed for each texture, giving a 2X increase in compression ratio for textures of mixed detail. Finally, a texture storage representation that is decoded at runtime on the GPU is presented. The decoded texture is still compressed for graphics hardware but uses 2X fewer bytes for storage and network bandwidth.Doctor of Philosoph

Intersatellite clock synchronization and absolute ranging for gravitational wave detection in space

The Laser Interferometer Space Antenna (LISA) is a European Space Agency (ESA) large-scale space mission, aiming to detect gravitational waves (GWs) in the observation band of 0.1mHz to 1Hz. The constellation is formed by three spacecrafts (SCs), exchanging laser beams with each other. The detector adopts heterodyne interferometry with MHz frequency offsets. GW signals are then encoded in optical beatnote phases, and the phase information has to be extracted by a core device called phasemeter (PM). Unequal and time- varying orbital motions introduce an overwhelming laser noise coupling that impedes the LISA performance levels of 10 ucycle/sqrt(Hz). Thereby, the post-processing technique called time-delay interferometry (TDI) time-shifts phase signals to synthesize virtual equal-arm interferometers. TDI requires absolute-ranging information, as its input, to the accuracy of 1 m rms, which will be provided by monitors like pseudo-random noise ranging (PRNR) and time-delay interferometry ranging (TDIR). An additional challenge is independent clocks on each SC that time-stamp PM data. This, alongside TDI, requires the synchronization of the onboard clocks in post-processing. This thesis reports on the experimental demonstrations of such key components for LISA. This is done by extending the scope of the hexagonal optical testbed at the Albert Einstein Institute (AEI): the "Hexagon". The first part of the thesis focuses on clock synchronization, utilizing the TDIR-like algorithm. With representative technologies both in devices and data analysis, this shows a new benchmark performance of LISA clock synchronization, achieving a 1 ucycle/sqrt(Hz) mark above 60 mHz and a TDIR accuracy of 1.84 m in range. This part also includes the first-ever verification of three noise couplings stemming from TDI and clock synchronization in an optical experiment. The second part of the thesis evolves the Hexagon further with PRNR. It commences with a review of the latest development using a transmission/reception loopback on a single hardware platform. This is followed by the research on the impact of the pseudo-random noise (PRN) modulation on phase tracking. This reveals that the codes, used at best knowledge so far, hinder the carrier phase extraction from achieving the 1 ucycle/sqrt(Hz) mark with realistic data encoded for intersatellite data communication. Some adaptations of PRN codes are proposed, and it is shown that these offer enough suppression of the noise coupling into phase tracking. After phase tracking is confirmed to be compatible with PRN modulations, PRNR itself is inves- tigated. The key novelty of this thesis in terms of PRNR is the study of its absolute-ranging feature, while previous research on this technology focused on stochastic noise properties. This requires the resolution of PRNR ambiguity and the correction of ranging biases. There suggests that the PRNR estimate, alongside some calibrations, can constantly function as absolute ranging with sub-meter accuracy

ParticleNeRF: A Particle-Based Encoding for Online Neural Radiance Fields

While existing Neural Radiance Fields (NeRFs) for dynamic scenes are offline methods with an emphasis on visual fidelity, our paper addresses the online use case that prioritises real-time adaptability. We present ParticleNeRF, a new approach that dynamically adapts to changes in the scene geometry by learning an up-to-date representation online, every 200ms. ParticleNeRF achieves this using a novel particle-based parametric encoding. We couple features to particles in space and backpropagate the photometric reconstruction loss into the particles' position gradients, which are then interpreted as velocity vectors. Governed by a lightweight physics system to handle collisions, this lets the features move freely with the changing scene geometry. We demonstrate ParticleNeRF on various dynamic scenes containing translating, rotating, articulated, and deformable objects. ParticleNeRF is the first online dynamic NeRF and achieves fast adaptability with better visual fidelity than brute-force online InstantNGP and other baseline approaches on dynamic scenes with online constraints. Videos of our system can be found at our project website https://sites.google.com/view/particlenerf