3D Weather – Towards a Real-time 3D Simulation of Localised Weather presented at EVA 2011

Weather forecasts are nearly always portrayed from either a satellite view perspective, a numerical or symbol based representation. None of these methods actually portray weather visually from the point of view of the observer, that is, they do not represent our experience of weather. This problem presents a challenge to displaying weather using real-time 3D computer graphics. 3D Weather is a proposed method to solve this problem, to create more believable representations of the weather using real weather data. By employing computer graphic techniques and computer game concepts the project intends to create a localized display of weather using mapping and weather data. Started in 2010, the project has been exploring existing techniques, scoping out the needs of stakeholders (such as the Met Office), and creating a prototype to explore the issues. The paper concludes that the quest for realism with computer graphics can be a double-edged sword. It can lead to expectations of accuracy in the data its meant to represent, which can be desired, but in the case of the weather forecast the representation is not necessary what the weather will be, its what the weather might be. The continuing project will explore the balance of issues when representing the weather for past events as well as for forecasts

Large-scale cloudscapes using noise

Clouds have been of particular interest in computer graphics due to the challenge they present. Clouds are considered fuzzy objects, and need specialized algorithms to model and render realistically. Many techniques exist to model and render clouds that have had much success. This research will take existing techniques in cloud modeling and rendering and create a new technique combining those with noise. The idea is that noise can be used to model large-scale repeatable 3D cloudscapes and to be able to model such cloudscapes much more quickly than current techniques. This would be beneficial to developers of virtual universes that have very many worlds numbering in the ten to hundreds to create convincing cloudscapes on each distinct world

Atmospheric cloud representation methods in computer graphics: A review

Cloud representation is one of the important components in the atmospheric cloud visualization system. Lack of review papers on the cloud representation methods available in the area of computer graphics has directed towards the difficulty for researchers to understand the appropriate solutions. Therefore, this paper aims to provide a comprehensive review of the atmospheric cloud representation methods that have been proposed in the computer graphics domain, involving the classical and the current state-of-the-art approaches. The reviewing process was conducted by searching, selecting, and analyzing the prominent articles collected from online digital libraries and search engines. We highlighted the taxonomic classification of the existing cloud representation methods in solving the atmospheric cloud-related problems. Finally, research issues and directions in the area of cloud representations and visualization have been discussed. This review would be significantly beneficial for researchers to clearly understand the general picture of the existing methods and thus helping them in choosing the best-suited approach for their future research and development

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

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

Atmospheric cloud modeling methods in computer graphics: A review, trends, taxonomy, and future directions

The modeling of atmospheric clouds is one of the crucial elements in the natural phenomena visualization system. Over the years, a wide range of approaches has been proposed on this topic to deal with the challenging issues associated with visual realism and performance. However, the lack of recent review papers on the atmospheric cloud modeling methods available in computer graphics makes it difficult for researchers and practitioners to understand and choose the well-suited solutions for developing the atmospheric cloud visualization system. Hence, we conducted a comprehensive review to identify, analyze, classify, and summarize the existing atmospheric cloud modeling solutions. We selected 113 research studies from recognizable data sources and analyzed the research trends on this topic. We defined a taxonomy by categorizing the atmospheric cloud modeling methods based on the methods' similar characteristics and summarized each of the particular methods. Finally, we underlined several research issues and directions for potential future work. The review results provide an overview and general picture of the atmospheric cloud modeling methods that would be beneficial for researchers and practitioners

Deep Dynamic Cloud Lighting

Sky illumination is a core source of lighting in rendering, and a substantial amount of work has been developed to simulate lighting from clear skies. However, in reality, clouds substantially alter the appearance of the sky and subsequently change the scene's illumination. While there have been recent advances in developing sky models which include clouds, these all neglect cloud movement which is a crucial component of cloudy sky appearance. In any sort of video or interactive environment, it can be expected that clouds will move, sometimes quite substantially in a short period of time. Our work proposes a solution to this which enables whole-sky dynamic cloud synthesis for the first time. We achieve this by proposing a multi-timescale sky appearance model which learns to predict the sky illumination over various timescales, and can be used to add dynamism to previous static, cloudy sky lighting approaches.Comment: Project page: https://pinarsatilmis.github.io/DDC

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

Procedural Cloudscapes

International audienceWe present a phenomenological approach for modeling and animating cloudscapes. We propose a compact procedural model for representing the different types of cloud over a range of altitudes. We define primitive-based field functions that allow the user to control and author the cloud cover over large distances easily. Our approach allows us to animate cloudscapes by morphing: instead of simulating the evolution of clouds using a physically-based simulation, we compute the movement of clouds using key-frame interpolation and tackle the morphing problem as an Optimal Transport problem. The trajectories of the cloud cover primitives are generated by solving an Anisotropic Shortest Path problem with a cost function that takes into account the elevation of the terrain and the parameters of the wind field

Realistic natural atmospheric phenomena and weather effects for interactive virtual environments.

Clouds and the weather are important aspects of any natural outdoor scene, but existing dynamic techniques within computer graphics only offer the simplest of cloud representations. The problem that this work looks to address is how to provide a means of simulating clouds and weather features such as precipitation, that are suitable for virtual environments. Techniques for cloud simulation are available within the area of meteorology, but numerical weather prediction systems are computationally expensive, give more numerical accuracy than we require for graphics and are restricted to the laws of physics. Within computer graphics, we often need to direct and adjust physical features or to bend reality to meet artistic goals, which is a key difference between the subjects of computer graphics and physical science. Pure physicallybased simulations, however, evolve their solutions according to pre-set rules and are notoriously difficult to control. The challenge then is for the solution to be computationally lightweight and able to be directed in some measure while at the same time producing believable results. This work presents a lightweight physically-based cloud simulation scheme that simulates the dynamic properties of cloud formation and weather effects. The system simulates water vapour, cloud water, cloud ice, rain, snow and hail. The water model incorporates control parameters and the cloud model uses an arbitrary vertical temperature profile, with a tool described to allow the user to define this. The result of this work is that clouds can now be simulated in near real-time complete with precipitation. The temperature profile and tool then provide a means of directing the resulting formation