A Realistic, Generic Earth/Atmosphere Model - CS348B Final Project
Dick Brouwer
Overview
Rendering scenes, especially outdoors, generally involves using manually created environment maps or other 'hacks' to realistically render skylight. Especially for twilight scenes with very diverse lightning conditions no suitable tools are available (to my knowledge). I want to create a generic model for rendering a realistic sky for a given position on the earth, season, time of day and atmosphere condition (e.g. foggy, polluted etc.). Developing a flexible model would eliminate the use for many of us to re-create the effects of outdoor lighting. If my model turns out to be very computational intensive, it could at least be used to pre-process realistic environment maps to be re-used in renderings.
To accurately render skylights many atmospheric effects have to be taken into account, inluding:
- solar irradiance spectrum and its absorption in the ozone layer,
- wavelength-dependent refraction of direct sunlight in the atmosphere,
- climate-dependent composition and size distribution of aerosols / dust particles,
- height-dependent air, humidity, and aerosol density,
- Rayleigh scattering (air molecules) and Mie scattering (aerosols),
- radiative transfer (multiple scattering), as well as
- the shadow of the Earth.
While there have been many attemps to take some of these effects into account, not many have tried to do all. 2 papers i) Jorg Haber, Marcus Magnor and Hans-Pieter Seidel: "Physically Based Simulation of Twilight Phenomena" and "Realistic Solar Disc Rendering" by Andrei Lintu, Jorg Haber and Marcus Magnor present a generic approach to tackle these issues and provide a strong basis for me to build off from.
Example images of beautifull skylights are plentifull of course. Here are some examples of the images I would like to reproduce:
Approach
As a first step I need to model the sun's position relative to the earth given certain input parameters. Because this calculation does not need to be dead-on accurate I can make some simplifying assumptions like using a spherical earth. This should make these calculations fairly straighforward. My input parameters would be: "Time-of-day", "Position on Earth (latitude/longitude)" and "Day-of-year (seasonal dependence)".
Next to calculating the position of the sun I need to collect data on atmospheric conditions. Some I will asume fixed (e.g. athmosphere temperature layers etc.) and others will be parameterized like humidity, dust and pollution