Realistic simulation and animation of clouds using SkewT-LogP diagrams

Nuvens e clima são tópicos importantes em computação gráfica, nomeadamente na simulação e animação de fenómenos naturais. Tal deve-se ao facto de a simulação de fenómenos naturais−onde as nuvens estão incluídas−encontrar aplicações em filmes, jogos e simuladores de voo. Contudo, as técnicas existentes em computação gráfica apenas permitem representações de nuvens simplificadas, tornadas possíveis através de dinâmicas fictícias que imitam a realidade. O problema que este trabalho pretende abordar prende-se com a simulação de nuvens adequadas para utilização em ambientes virtuais, isto é, nuvens com dinâmica baseada em física que variam ao longo do tempo. Em meteorologia é comum usar técnicas de simulação de nuvens baseadas em leis da física, contudoossistemasatmosféricosdeprediçãonuméricasãocomputacionalmente pesados e normalmente possuem maior precisão numérica do que o necessário em computação gráfica. Neste campo, torna-se necessário direcionar e ajustar as características físicas ou contornar a realidade de modo a atingir os objetivos artísticos, sendo um fator fundamental que faz com que a computação gráfica se distinga das ciências físicas. Contudo, simulações puramente baseadas em física geram soluções de acordo com regras predefinidas e tornam-se notoriamente difíceis de controlar. De modo a enfrentar esses desafios desenvolvemos um novo método de simulação de nuvens baseado em física que possui a característica de ser computacionalmente leve e simula as propriedades dinâmicas relacionadas com a formação de nuvens. Este novo modelo evita resolver as equações físicas, ao apresentar uma solução explícita para essas equações através de diagramas termodinâmicos SkewT/LogP. O sistema incorpora dados reais de forma a simular os parâmetros necessários para a formação de nuvens. É especialmente adequado para a simulação de nuvens cumulus que se formam devido ao um processo convectivo. Esta abordagem permite não só reduzir os custos computacionais de métodos baseados em física, mas também fornece a possibilidade de controlar a forma e dinâmica de nuvens através do controlo dos níveis atmosféricos existentes no diagrama SkewT/LogP. Nestatese,abordámostambémumoutrodesafio,queestárelacionadocomasimulação de nuvens orográficas. Do nosso conhecimento, esta é a primeira tentativa de simular a formação deste tipo de nuvens. A novidade deste método reside no fato de este tipo de nuvens serem não convectivas, oque se traduz nocálculodeoutrosníveis atmosféricos. Além disso, atendendo a que este tipo de nuvens se forma sobre montanhas, é também apresentadoumalgoritmoparadeterminarainfluênciadamontanhasobreomovimento da nuvem. Em resumo, esta dissertação apresenta um conjunto de algoritmos para a modelação e simulação de nuvens cumulus e orográficas, recorrendo a diagramas termodinâmicos SkewT/LogP pela primeira vez no campo da computação gráfica.Clouds and weather are important topics in computer graphics, in particular in the simulation and animation of natural phenomena. This is so because simulation of natural phenomena−where clouds are included−find applications in movies, games and flight simulators. However, existing techniques in computer graphics only offer the simplified cloud representations, possibly with fake dynamics that mimic the reality. The problem that this work addresses is how to find realistic simulation of cloud formation and evolution, that are suitable for virtual environments, i.e., clouds with physically-based dynamics over time. It happens that techniques for cloud simulation are available within the area of meteorology, but numerical weather prediction systems based on physics laws are computationally expensive and provide more numerical accuracy than the required accuracy in computer graphics. In computer graphics, we often need to direct and adjust physical features, or even to bend the reality, to meet artistic goals, which is a key factor that makes computer graphics distinct from physical sciences. However, pure physically-based simulations evolve their solutions according to pre-set physics rules that are notoriously difficult to control. In order to face these challenges we have developed a new lightweight physically-based cloudsimulationschemethatsimulatesthedynamicpropertiesofcloudformation. This new model avoids solving the physically-based equations typically used to simulate the formation of clouds by explicitly solving these equations using SkewT/LogP thermodynamic diagrams. The system incorporates a weather model that uses real data to simulate parameters related to cloud formation. This is specially suitable to the simulation of cumulus clouds, which result from a convective process. This approach not only reduces the computational costs of previous physically-based methods, but also provides a technique to control the shape and dynamics of clouds by handling the cloud levels in SkewT/LogP diagrams. In this thesis, we have also tackled a new challenge, which is related to the simulation oforographic clouds. From ourknowledge, this isthefirstattempttosimulatethis type of cloud formation. The novelty in this method relates to the fact that these clouds are non-convective, so that different atmospheric levels have to be determined. Moreover, since orographic clouds form over mountains, we have also to determine the mountain influence in the cloud motion. In summary, this thesis presents a set of algorithms for the modelling and simulation of cumulus and orographic clouds, taking advantage of the SkewT/LogP diagrams for the first time in the field of computer graphics

Real-time rendering of physically-based cloud simulations for university undergraduate research fellows

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references (leaves 38-39).Computers today employ simulations of physical phenomena such as wind and fire and other physical properties in many common applications, including programs meant for training and entertainment. We focus particularly on the realistic simulation of cloud formation and existence on current commercially-available computers. One of the challenges associated with this simulation is its display onto a computer screen, often referred to as rendering. We will present a brief overview of existing cloud rendering techniques and compare their effectiveness to rendering a simulation as it occurs. We will then suggest our rendering method which relies upon the use of three-dimensional textures and modified Gaussian transfer functions for the self-shadowing properties associated with clouds. We will analyze these results, focusing on frame rates and visual appearance, and then conclude by suggesting further work on this topic

Ray casting implicit fractal surfaces with reduced affine arithmetic

A method is presented for ray casting implicit surfaces defined by fractal combinations of procedural noise functions. The method is robust and uses affine arithmetic to bound the variation of the implicit function along a ray. The method is also efficient due to a modification in the affine arithmetic representation that introduces a condensation step at the end of every non-affine operation. We show that our method is able to retain the tight estimation capabilities of affine arithmetic for ray casting implicit surfaces made from procedural noise functions while being faster to compute and more efficient to store

Striatal Volume Predicts Level of Video Game Skill Acquisition

Video game skills transfer to other tasks, but individual differences in performance and in learning and transfer rates make it difficult to identify the source of transfer benefits. We asked whether variability in initial acquisition and of improvement in performance on a demanding video game, the Space Fortress game, could be predicted by variations in the pretraining volume of either of 2 key brain regions implicated in learning and memory: the striatum, implicated in procedural learning and cognitive flexibility, and the hippocampus, implicated in declarative memory. We found that hippocampal volumes did not predict learning improvement but that striatal volumes did. Moreover, for the striatum, the volumes of the dorsal striatum predicted improvement in performance but the volumes of the ventral striatum did not. Both ventral and dorsal striatal volumes predicted early acquisition rates. Furthermore, this early-stage correlation between striatal volumes and learning held regardless of the cognitive flexibility demands of the game versions, whereas the predictive power of the dorsal striatal volumes held selectively for performance improvements in a game version emphasizing cognitive flexibility. These findings suggest a neuroanatomical basis for the superiority of training strategies that promote cognitive flexibility and transfer to untrained tasks.United States. Office of Naval Research (grant number N00014-07-1-0903

Model for volume lighting and modeling

Journal ArticleAbstract-Direct volume rendering is a commonly used technique in visualization applications. Many of these applications require sophisticated shading models to capture subtle lighting effects and characteristics of volumetric data and materials. For many volumes, homogeneous regions pose problems for typical gradient-based surface shading. Many common objects and natural phenomena exhibit visual quality that cannot be captured using simple lighting models or cannot be solved at interactive rates using more sophisticated methods. We present a simple yet effective interactive shading model which captures volumetric light attenuation effects that incorporates volumetric shadows, an approximation to phase functions, an approximation to forward scattering, and chromatic attenuation that provides the subtle appearance of translucency. We also present a technique for volume displacement or perturbation that allows realistic interactive modeling of high frequency detail for both real and synthetic volumetric data

Volumetric cloud generation using a Chinese brush calligraphy style

Includes bibliographical references.Clouds are an important feature of any real or simulated environment in which the sky is visible. Their amorphous, ever-changing and illuminated features make the sky vivid and beautiful. However, these features increase both the complexity of real time rendering and modelling. It is difficult to design and build volumetric clouds in an easy and intuitive way, particularly if the interface is intended for artists rather than programmers. We propose a novel modelling system motivated by an ancient painting style, Chinese Landscape Painting, to address this problem. With the use of only one brush and one colour, an artist can paint a vivid and detailed landscape efficiently. In this research, we develop three emulations of a Chinese brush: a skeleton-based brush, a 2D texture footprint and a dynamic 3D footprint, all driven by the motion and pressure of a stylus pen. We propose a hybrid mapping to generate both the body and surface of volumetric clouds from the brush footprints. Our interface integrates these components along with 3D canvas control and GPU-based volumetric rendering into an interactive cloud modelling system. Our cloud modelling system is able to create various types of clouds occurring in nature. User tests indicate that our brush calligraphy approach is preferred to conventional volumetric cloud modelling and that it produces convincing 3D cloud formations in an intuitive and interactive fashion. While traditional modelling systems focus on surface generation of 3D objects, our brush calligraphy technique constructs the interior structure. This forms the basis of a new modelling style for objects with amorphous shape

A Technique for Art Direction of Physically Based Fire Simulation

This thesis presents an innovative way to art direct individual flames in a physically based fire simulation. Fire, due to its warm colors and constant movement, often becomes the main attraction to the viewer\u27s eye in a scene. This technique provides control over this chaotic natural phenomenon at a microscopic level, enabling the artist to add character to flames and create highly stylized visuals. The fire system itself is a fully physics based two gas system with fuel gas and heat, with flames advected along convection currents generated by combustion. The technique is applied to examples of highly stylized flame artwork and rendered results of the art directed simulations are presented. A full description of the implementation and performance of the fire system and the control method is also presented

Distribution of perfluorooctanesulfonate (PFOS) isomers in a Norwegian arctic food web

Perfluorooctanesulfonate (PFOS) is a global synthetic fluoroorganic compound and one of the most abundant per- and polyfluorinated alkylated substances (PFAS) in the arctic environment. PFAS are ubiquitously dispersed throughout the planet’s aquatic environments, soils and wildlife. Their environmental persistence, tendency to bioaccumulate and biomagnify in food webs coupled with negative health effects at elevated levels has resulted in them being commonly described as persistent organic pollutants. Although PFOS and other PFAS compounds have been subject to increasing scientific interest in the decades following their discovery, much remains unknown and uncertain in regards to their global and local transport mechanisms as well as their potential as environmental toxins. The objective of this study was to develop and validate an analytical method for the separation and determination of the individual PFOS isomers commonly found in environmental and technical samples, and attempt to quantitate them in biota samples from Svalbard, Norway. Collected samples from neighbouring levels of the food web at two different locations in the vicinity of Longyearbyen were analysed for the purpose of gaining insight into the levels of the individual PFOS-isomers, and changes happening to the isomer profile from one trophic level to the next. A new high performance liquid chromatography mass spectrometry (HPLC-MS/MS) analytical method was designed by combining elements from other published studies. The method was used to separate four groups of PFOS isomers from a mixture and was applied to quantitate PFOS isomers in the biota samples. It was found that the total PFOS concentrations and the relative concentrations of L-PFOS in the biota samples increased with increasing trophic levels, in agreement with previous reports on the isomer’s greater bioaccumulation tendency. Fish liver samples from a reference station without any known nearby local PFOS pollution sources were discovered to have higher total PFOS levels than fish liver samples from a station near a decommissioned fire-fighting station. However, a small sample size and uncertainty with regards to the quantitation made it hard to interpret the findings, as PFOS isomers at lower trophic levels were not detected due to insufficient sensitivity.Perfluoroktansulfonat (PFOS) er en syntetisk fluoroorganisk forbindelse og en av de mest utbredte per- og polyfluorinerte alkylerte stoffene (PFAS) i arktiske miljøer. PFAS er svært utbredt og er spredt over hele verdens akvatiske miljøer, jord og dyreliv. Deres persistente natur, tendens til å bioakkumulere og magnifisere I næringskjeder, samt deres negative helseeffekter ved forhøyede nivåer har gjort at de regnes som persistente organiske forurensningsstoffer. Selv om PFOS og andre PFAS forbindelser har vært gjenstand fot økende vitenskapelig interesse in tiårene etter deres oppdagelse, er det fortsatt mye som ikke er kjent når det kommer til deres globale og lokale transportmekanismer og deres potensiale som miljøgifter. Formålet med denne studien var å utvikle og validere en analytisk metode til separasjon og bestemmelse and de individuelle PFOS isomerene tilstede i miljøprøver og i teknisk produkt, og forsøke å kvantifisere disse i biota-prøver fra Svalbard, Norge. Sampleprøver fra nærliggende trofiske nivåer i næringskjeden fra to ulike lokasjoner i området rundt Longyearbyen ble analysert i et forsøk på å skaffe seg innsikt i mengdene av de individuelle PFOS-isomerene, og hvordan isomerprofilen forandrer seg fra ett trofisk nivå til det neste. En ny analytisk HPLC-MS/MS metode ble utviklet ved å kombinere elementer fra andre publiserte studier. Metoden ble brukt til å separere fire grupper PFOS isomerer fra en blanding og ble brukt til å separere fire grupper PFOS-isomerer fra en blanding og ble så benyttet til å kvantifisere isomerer i biotaprøvene. Det ble påvist at den totale PFOS konsentrasjonen og de relative L-PFOS konsentrasjonen i biotaprøvene økte høyere opp i næringskjeden, i samsvar med tidligere rapporten om isomerens større bioakkumuleringsegenskaper. Fikseleverprøver fra en referansestasjon uten kjente nærliggende PFOS utslippskilder ble funnet å ha høyere total-PFOS konsentrasjoner enn fiskeleverprøver fra en stasjon nær en nedlagt brannøvelsesstasjon. Det lave prøveantallet og usikkerhet tilknyttet kvantifiseringen gjorde det vanskelig å tolke funnene, siden PFOS isomerer ikke ble kvantifisert ved lavere trofiske nivåer på grunn av utilstrekkelig sensitivitet.M-KJEM

Isosurface modelling of soft objects in computer graphics.

There are many different modelling techniques used in computer graphics to describe a wide range of objects and phenomena. In this thesis, details of research into the isosurface modelling technique are presented. The isosurface technique is used in conjunction with more traditional modelling techniques to describe the objects needed in the different scenes of an animation. The isosurface modelling technique allows the description and animation of objects that would be extremely difficult, or impossible to describe using other methods. The objects suitable for description using isosurface modelling are soft objects. Soft objects merge elegantly with each other, pull apart, bubble, ripple and exhibit a variety of other effects. The representation was studied in three phases of a computer animation project: modelling of the objects; animation of the objects; and the production of the images. The research clarifies and presents many algorithms needed to implement the isosurface representation in an animation system. The creation of a hierarchical computer graphics animation system implementing the isosurface representation is described. The scalar fields defining the isosurfaces are represented using a scalar field description language, created as part of this research, which is automatically generated from the hierarchical description of the scene. This language has many techniques for combining and building the scalar field from a variety of components. Surface attributes of the objects are specified within the graphics system. Techniques are described which allow the handling of these attributes along with the scalar field calculation. Many animation techniques specific to the isosurface representation are presented. By the conclusion of the research, a graphics system was created which elegantly handles the isosurface representation in a wide variety of animation situations. This thesis establishes that isosurface modelling of soft objects is a powerful and useful technique which has wide application in the computer graphics community