Virtuális világok szimulációja és megjelenítése = Simulation-Rendering in Virtual Reality Systems

1. A Navier-Stokes egyenletek Lagrange-i és Euler-i nézőpontjának masszívan párhuzamos architektúrán végrehajtható hatékony megoldási algoritmusa folyadékszimulációhoz. A folyadék szabályozása, azaz előírt sűrűségfüggvény felé terelése. 2. Formális nyelvek, L-rendszerek párhuzamos kiértékelési algoritmusa és alkalmazás ""végtelen"" városok és növények szimulációjára. 3. Térfogati modellekben a fényterjedés szimuláció szabad úthossz mintavételezésének hatékony megoldása, amely heterogén közegben extrém nagy felbontásokra (pl. 32 ezer köbös) is működik. 4. Térfogati modellek véges elemes megoldásához az iterációt gyorsító kezdeti becslő kialakítása. 5. A fotonterjedés szimulációjának felhasználása inverz feladatokban, pozitron emissziós tomográfiához rekonstrukciós eljárások kidolgozása. 6. A Koksma-Hlawka egyenlőtlenség általánosítása nem egyenletes minták esetére és ez alapján delta-szigma modulációs módszer kidolgozása fontosság szerinti mintavételezéshez. 7. Az ambiens takarási módszer új geometriai értelmezésének megalkotása és új, hatékony módszerek kidolgozása. 8. Out-of-core vizualizáció sugárkövetés alapon, több száz millió háromszögből álló modellek interaktív bejárása. 9. Az NPR algoritmusoknál a 3D konzisztencia biztosítása, és animációs algoritmusok létrehozása. | 1. Algorithms for the solution of the Navier-Stokes equations of fluids on massively parallel hardware, taking both the Eulerian and Lagrangian viewpoints. Solution of the fluid control problem. 2. Parallel evaluation of L-systems and its application to procedural infinite virtual worlds. 3. Free path sampling method for high resolution, heterogeneous participating media. 4. Bootstrapping the iterative solver of finite element approaches for light transport in participating media. 5. Development of a parallel solver for the photon transport problem and its application in positron emission tomography. 6. Generalization of Koksma-Hlawka inequality and the development of a delta-sigma type importance sampling. 7. New geometric interpretation for ambient occlusion and novel computation algorithms. 8. Out-of-core visualization methods based on ray tracing. 9. Solution of the 3D consistency problem of NPR and extension to animation sequences

Stochastic Volume Rendering of Multi-Phase SPH Data

In this paper, we present a novel method for the direct volume rendering of large smoothed‐particle hydrodynamics (SPH) simulation data without transforming the unstructured data to an intermediate representation. By directly visualizing the unstructured particle data, we avoid long preprocessing times and large storage requirements. This enables the visualization of large, time‐dependent, and multivariate data both as a post‐process and in situ. To address the computational complexity, we introduce stochastic volume rendering that considers only a subset of particles at each step during ray marching. The sample probabilities for selecting this subset at each step are thereby determined both in a view‐dependent manner and based on the spatial complexity of the data. Our stochastic volume rendering enables us to scale continuously from a fast, interactive preview to a more accurate volume rendering at higher cost. Lastly, we discuss the visualization of free‐surface and multi‐phase flows by including a multi‐material model with volumetric and surface shading into the stochastic volume rendering

Interactive Rendering Framework for Distance Function Representations

Sphere tracing, introduced by Hart in [5], is an efficient method to find ray- surface intersections, provided the surface is represented by a signed distance function (SDF) or a lower estimate of it. This paper presents an interactive rendering framework for visualising exact and estimate SDF representations. We demonstrate the performance of the system by visualising 3D fractals and its modularity by rendering algebraic and meta surfaces. In addition, we discuss SDF estimation of algebraic surfaces

GPU Based Real-time Welding Simulation with Smoothed-Particle Hydrodynamics

Welding training is essential in the development of industrialization. A good welder will build robust workpieces that ensure the safety and stability of the product. However, training a welder requires lots of time and access professional welding equipment. Therefore, it is desirable to have a training system that is economical and easy to use. After decades development of computer graphics, sophisticated methodologies are developed in simulation fields, along the advanced hardware, enables the possibility of simulation welding with software. In this thesis, a novel prototype of welding training system is proposed. We use smoothed-particle hydrodynamics (SPH) method to simulate fluid as well as heat transfer and phase changing. In order to accelerate the processing to reach the level of real-time, we adopt CUDA to implement the SPH solver on GPU. Plus, Leap Motion is utilized as the input device to control the welding gun. As the result, the simulation reaches decent frame rate that allows the user control the simulation system interactively. The input device permits the user to adapt to the system in less than 5 minutes. This prototype shows a new direction in the training system that combines VR, graphics, and physics simulation. The further development of VR output device like Oculus Rift will enable the training system to a more immersive level

Modeling and real-time rendering of participating media using the GPU

Cette thèse traite de la modélisation, l'illumination et le rendu temps-réel de milieux participants à l'aide du GPU. Dans une première partie, nous commençons par développer une méthode de rendu de nappes de brouillard hétérogènes pour des scènes en extérieur. Le brouillard est modélisé horizontalement dans une base 2D de fonctions de Haar ou de fonctions B-Spline linéaires ou quadratiques, dont les coefficients peuvent être chargés depuis une textit{fogmap}, soit une carte de densité en niveaux de gris. Afin de donner au brouillard son épaisseur verticale, celui-ci est doté d'un coefficient d'atténuation en fonction de l'altitude, utilisé pour paramétrer la rapidité avec laquelle la densité diminue avec la distance au milieu selon l'axe Y. Afin de préparer le rendu temps-réel, nous appliquons une transformée en ondelettes sur la carte de densité du brouillard, afin d'en extraire une approximation grossière (base de fonctions B-Spline) et une série de couches de détails (bases d'ondelettes B-Spline), classés par fréquence.%Les détails sont ainsi classés selon leur fréquence et, additionnées, permettent de retrouver la carte de densité d'origine. Chacune de ces bases de fonctions 2D s'apparente à une grille de coefficients. Lors du rendu sur GPU, chacune de ces grilles est traversée pas à pas, case par case, depuis l'observateur jusqu'à la plus proche surface solide. Grâce à notre séparation des différentes fréquences de détails lors des pré-calculs, nous pouvons optimiser le rendu en ne visualisant que les détails les plus contributifs visuellement en avortant notre parcours de grille à une distance variable selon la fréquence. Nous présentons ensuite d'autres travaux concernant ce même type de brouillard : l'utilisation de la transformée en ondelettes pour représenter sa densité via une grille non-uniforme, la génération automatique de cartes de densité et son animation à base de fractales, et enfin un début d'illumination temps-réel du brouillard en simple diffusion. Dans une seconde partie, nous nous intéressons à la modélisation, l'illumination en simple diffusion et au rendu temps-réel de fumée (sans simulation physique) sur GPU. Notre méthode s'inspire des Light Propagation Volumes (volume de propagation de lumière), une technique à l'origine uniquement destinée à la propagation de la lumière indirecte de manière complètement diffuse, après un premier rebond sur la géométrie. Nous l'adaptons pour l'éclairage direct, et l'illumination des surfaces et milieux participants en simple diffusion. Le milieu est fourni sous forme d'un ensemble de bases radiales (blobs), puis est transformé en un ensemble de voxels, ainsi que les surfaces solides, de manière à disposer d'une représentation commune. Par analogie aux LPV, nous introduisons un Occlusion Propagation Volume, dont nous nous servons, pour calculer l'intégrale de la densité optique entre chaque source et chaque autre cellule contenant soit un voxel du milieu, soit un voxel issu d'une surface. Cette étape est intégrée à la boucle de rendu, ce qui permet d'animer le milieu participant ainsi que les sources de lumière sans contrainte particulière. Nous simulons tous types d'ombres : dues au milieu ou aux surfaces, projetées sur le milieu ou les surfacesThis thesis deals with modeling, illuminating and rendering participating media in real-time using graphics hardware. In a first part, we begin by developing a method to render heterogeneous layers of fog for outdoor scenes. The medium is modeled horizontally using a 2D Haar or linear/quadratic B-Spline function basis, whose coefficients can be loaded from a fogmap, i.e. a grayscale density image. In order to give to the fog its vertical thickness, it is provided with a coefficient parameterizing the extinction of the density when the altitude to the fog increases. To prepare the rendering step, we apply a wavelet transform on the fog's density map, and extract a coarse approximation and a series of layers of details (B-Spline wavelet bases).These details are ordered according to their frequency and, when summed back together, can reconstitute the original density map. Each of these 2D function basis can be viewed as a grid of coefficients. At the rendering step on the GPU, each of these grids is traversed step by step, cell by cell, since the viewer's position to the nearest solid surface. Thanks to our separation of the different frequencies of details at the precomputations step, we can optimize the rendering by only visualizing details that contribute most to the final image and abort our grid traversal at a distance depending on the grid's frequency. We then present other works dealing with the same type of fog: the use of the wavelet transform to represent the fog's density in a non-uniform grid, the automatic generation of density maps and their animation based on Julia fractals, and finally a beginning of single-scattering illumination of the fog, where we are able to simulate shadows by the medium and the geometry. In a second time, we deal with modeling, illuminating and rendering full 3D single-scattering sampled media such as smoke (without physical simulation) on the GPU. Our method is inspired by light propagation volumes, a technique whose only purpose was, at the beginning, to propagate fully diffuse indirect lighting. We adapt it to direct lighting, and the illumination of both surfaces and participating media. The medium is provided under the form of a set of radial bases (blobs), and is then transformed into a set of voxels, together with solid surfaces, so that both entities can be manipulated more easily under a common form. By analogy to the LPV, we introduce an occlusion propagation volume, which we use to compute the integral of the optical density, between each source and each other cell containing a voxel either generated from the medium, or from a surface. This step is integrated into the rendering process, which allows to animate participating media and light sources without any further constraintPARIS-EST-Université (770839901) / SudocSudocFranceF

Real-Time deep image rendering and order independent transparency

In computer graphics some operations can be performed in either object space or image space. Image space computation can be advantageous, especially with the high parallelism of GPUs, improving speed, accuracy and ease of implementation. For many image space techniques the information contained in regular 2D images is limiting. Recent graphics hardware features, namely atomic operations and dynamic memory location writes, now make it possible to capture and store all per-pixel fragment data from the rasterizer in a single pass in what we call a deep image. A deep image provides a state where all fragments are available and gives a more complete image based geometry representation, providing new possibilities in image based rendering techniques. This thesis investigates deep images and their growing use in real-time image space applications. A focus is new techniques for improving fundamental operation performance, including construction, storage, fast fragment sorting and sampling. A core and driving application is order-independent transparency (OIT). A number of deep image sorting improvements are presented, through which an order of magnitude performance increase is achieved, significantly advancing the ability to perform transparency rendering in real time. In the broader context of image based rendering we look at deep images as a discretized 3D geometry representation and discuss sampling techniques for raycasting and antialiasing with an implicit fragment connectivity approach. Using these ideas a more computationally complex application is investigated — image based depth of field (DoF). Deep images are used to provide partial occlusion, and in particular a form of deep image mipmapping allows a fast approximate defocus blur of up to full screen size

Numerical modelling and visualization of the evolution of extensional fault systems

The purpose of this work is split into two categories, the first was to analyse the application of real-time Physics Engine software libraries for use in calculating a geological numerical model. Second was the analysis of the applicability of glyph and implicit surface based visualization techniques to explore fault systems produced by the model. The current state of the art in Physics Engines was explored by redeveloping a Discrete Element Model to be calculated using NVIDIA's PhysX engine. Analyses regarding the suitability of the engine in terms of numerical accuracy and developmental capabilities is given, as well as the definition of a specialised and bespoke parallelisation technique. The use of various glyph based visualizations is explored to define a new standardised taxonomy for geological data and the MetaBall visualization technique was applied to reveal three dimensional fault structures as an implicit surface. Qualitative analysis was undertaken in the form of a user study, comprising of interviews with expert geologists. The processing pipeline used by many Physics Engines was found to be comparable to the design of Discrete Element Model software, however, aspects of their design, such as integration accuracy, limitation to single precision floating point and imposed limits on the scale of n-body problem means their suitability is restricted to specific modelling cases. Glyph and implicit surface based visualization have been shown to be an effective way to present a geological Discrete Element Model, with the majority of experts interviewed able to perceive the fault structures that it contained. Development of a new engine, or modification of one that exists in accordance with the findings of this thesis would result in a library extremely well suited to the problem of rigid-body simulation for the sciences.EThOS - Electronic Theses Online ServiceNERCGBUnited Kingdo

Visuelle Analyse großer Partikeldaten

Partikelsimulationen sind eine bewährte und weit verbreitete numerische Methode in der Forschung und Technik. Beispielsweise werden Partikelsimulationen zur Erforschung der Kraftstoffzerstäubung in Flugzeugturbinen eingesetzt. Auch die Entstehung des Universums wird durch die Simulation von dunkler Materiepartikeln untersucht. Die hierbei produzierten Datenmengen sind immens. So enthalten aktuelle Simulationen Billionen von Partikeln, die sich über die Zeit bewegen und miteinander interagieren. Die Visualisierung bietet ein großes Potenzial zur Exploration, Validation und Analyse wissenschaftlicher Datensätze sowie der zugrundeliegenden Modelle. Allerdings liegt der Fokus meist auf strukturierten Daten mit einer regulären Topologie. Im Gegensatz hierzu bewegen sich Partikel frei durch Raum und Zeit. Diese Betrachtungsweise ist aus der Physik als das lagrange Bezugssystem bekannt. Zwar können Partikel aus dem lagrangen in ein reguläres eulersches Bezugssystem, wie beispielsweise in ein uniformes Gitter, konvertiert werden. Dies ist bei einer großen Menge an Partikeln jedoch mit einem erheblichen Aufwand verbunden. Darüber hinaus führt diese Konversion meist zu einem Verlust der Präzision bei gleichzeitig erhöhtem Speicherverbrauch. Im Rahmen dieser Dissertation werde ich neue Visualisierungstechniken erforschen, welche speziell auf der lagrangen Sichtweise basieren. Diese ermöglichen eine effiziente und effektive visuelle Analyse großer Partikeldaten