1,327 research outputs found
Path-tracing Monte Carlo Library for 3D Radiative Transfer in Highly Resolved Cloudy Atmospheres
Interactions between clouds and radiation are at the root of many
difficulties in numerically predicting future weather and climate and in
retrieving the state of the atmosphere from remote sensing observations. The
large range of issues related to these interactions, and in particular to
three-dimensional interactions, motivated the development of accurate radiative
tools able to compute all types of radiative metrics, from monochromatic, local
and directional observables, to integrated energetic quantities. In the
continuity of this community effort, we propose here an open-source library for
general use in Monte Carlo algorithms. This library is devoted to the
acceleration of path-tracing in complex data, typically high-resolution
large-domain grounds and clouds. The main algorithmic advances embedded in the
library are those related to the construction and traversal of hierarchical
grids accelerating the tracing of paths through heterogeneous fields in
null-collision (maximum cross-section) algorithms. We show that with these
hierarchical grids, the computing time is only weakly sensitivive to the
refinement of the volumetric data. The library is tested with a rendering
algorithm that produces synthetic images of cloud radiances. Two other examples
are given as illustrations, that are respectively used to analyse the
transmission of solar radiation under a cloud together with its sensitivity to
an optical parameter, and to assess a parametrization of 3D radiative effects
of clouds.Comment: Submitted to JAMES, revised and submitted again (this is v2
The development of local solar irradiance for outdoor computer graphics rendering
Atmospheric effects are approximated by solving the light transfer equation, LTE, of a given viewing path. The resulting accumulated spectral energy (its visible band) arriving at the observer’s eyes, defines the colour of the object currently on the line of sight. Due to the convenience of using a single rendering equation to solve the LTE for daylight sky and distant objects (aerial perspective), recent methods had opt for a similar kind of approach. Alas, the burden that the real-time calculation brings to the foil had forced these methods to make simplifications that were not in line with the actual world observation. Consequently, the results of these methods are laden with visual-errors. The two most common simplifications made were: i) assuming the atmosphere as a full-scattering medium only and ii) assuming a single density atmosphere profile. This research explored the possibility of replacing the real-time calculation involved in solving the LTE with an analytical-based approach. Hence, the two simplifications made by the previous real-time methods can be avoided. The model was implemented on top of a flight simulator prototype system since the requirements of such system match the objectives of this study. Results were verified against the actual images of the daylight skies. Comparison was also made with the previous methods’ results to showcase the proposed model strengths and advantages over its peers
A Qualitative and Quantitative Evaluation of 8 Clear Sky Models
We provide a qualitative and quantitative evaluation of 8 clear sky models
used in Computer Graphics. We compare the models with each other as well as
with measurements and with a reference model from the physics community. After
a short summary of the physics of the problem, we present the measurements and
the reference model, and how we "invert" it to get the model parameters. We
then give an overview of each CG model, and detail its scope, its algorithmic
complexity, and its results using the same parameters as in the reference
model. We also compare the models with a perceptual study. Our quantitative
results confirm that the less simplifications and approximations are used to
solve the physical equations, the more accurate are the results. We conclude
with a discussion of the advantages and drawbacks of each model, and how to
further improve their accuracy
Effect of finite terms on the truncation error of Mie series
The finite sum of the squares of the Mie coefficients is very useful for
addressing problems of classical light scattering. An approximate formula
available in the literature, and still in use today, has been developed to
determine a priori the number of the most significant terms needed to evaluate
the scattering cross section. Here we obtain an improved formula, which
includes the number of terms needed for determining the scattering cross
section within a prescribed relative error. This is accomplished using extended
precision computation, for a wide range of commonly used size parameters and
indexes of refraction. The revised formula for the finite number of terms can
be a promising and valuable approach for efficient modeling light scattering
phenomena.Comment: 3 pages, 3 figure
Advanced techniques for atmospheric effects
Over the last few years, open world videogames have been gaining lots of interest in the gaming industry. Open world videogames not only allow the player to freely roam over a vast terrain but also aim to recreate a believable dynamic world. Thus, one of the basic elements that such a videogame should feature is a day and night cycle. In this thesis, all of the intricacies that are involved in developing a physically based day and night cycle solution in a real-time rendering context are discussed. The main topics that will be covered are atmosphere rendering, celestial bodies positioning, celestial bodies rendering and nighttime scenes rendering
Real-Time Sky Color with Effect of Sun’s Position
In the rendering of outdoor scenes in virtual environments, the sun's position, sky color, clouds, shadow, trees, grass etc play very important roles in making it realistic. In this paper Sky color and the sun’s position are combined. Specific longitude, latitude, date and time are required parameters to calculate the exact position of the sun. The sun's position is calculated based on Julian dating; the sky’s color is created by Perez modeling. A functional application is designed to show the position of the sun and then sky color in arbitrary location, date and time. It can be possible to use this application in commercial games for outdoor rendering and for teachers to teach some part of physics about earth orbit and effect of the sun on the sky and it can be used in building design
A practical analytic model for daylight
www.cs.utah.edu Figure 1: Left: A rendered image of an outdoor scene with a constant colored sky and no aerial perspective. Right: The same image with a physically-based sky model and physically-based aerial perspective. Sunlight and skylight are rarely rendered correctly in computer graphics. A major reason for this is high computational expense. Another is that precise atmospheric data is rarely available. We present an inexpensive analytic model that approximates full spectrum daylight for various atmospheric conditions. These conditions are parameterized using terms that users can either measure or estimate. We also present an inexpensive analytic model that approximates the effects of atmosphere (aerial perspective). These models are fielded in a number of conditions and intermediate results verified against standard literature from atmospheric science. These models are analytic in the sense that they are simple formulas based on fits to simulated data; no explicit simulation is required to use them. Our goal is to achieve as much accuracy as possible without sacrificing usability
Atmospheric scattering - state of the art
Atmospheric scattering is the natural phenomenon mainly responsible for the colours we observe in the sky. Over the years, several realistic computer graphics algorithms have been proposed in order to reproduce these colours. This state of the art is motivated by the large amount of scattered information, and by its great potential usage in a wide range of applications like flight simulators, video games and movies. This paper will cover the most important models and will present their evolution over the years. The first part contains a small introduction to the mechanics behind the light scattering phenomena. The second part will cover the earlier models, very much focused in the physical phenomenon. The third section will cover GPU based models, more focused on performance.Fundação para a Ciência e a Tecnologia (FCT
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