The rendering of trees and snow in complex lighting environment is usually not very convincing, although there are techniques that should allow to improve its quality. That is why we picked an image that combined both tree and snow in an interesting way. Our goal will be to render as many of the features in the picture below as possible, focusing on the pine tree with all the lights, the other pine trees in the background and the snow lying on every object in the scene.
The modeling of the trees will be automated using a simple implementation of L-systems. We would like to simulate the gravity effect that bends branches towards the ground. The needles will be approximated by very simple objects, so that we can have a good density of them (probably 15000 - 30000 objects per trees). There is a bunch of papers and books on that topic, so that it should not be too difficult to get good documentation.
The snow will be modeled using meta-balls. These objects have also been abundantly documented. Preliminary experiences show that we can get good coverage by using 30000 sphere-based blobs to cover the ground. Our implementation will have to be particularly efficient to allow for reasonable rendering time. We plan to use LRT during a preprocessing stage to find the projection of the snow flakes on the objects of the scene by considering them as rays of light and using simple forward ray tracing to get their first intersection with an object of the scene.
The rendering of the snow will be done by implementing Jensen's subsurface scattering technique, as described in the papers A practical model for subsurface light transport (Jensen et al., SIGGRAPH 2000) and A rapid hierarchical rendering technique for translucent materials (Jensen at al., SIGGRAPH 2002).
The dark atmosphere, only breached by the moonlight and the electric lamps on the tree, makes it necessary to use global illumination techniques. There is an interesting approach using radiosity to render scenes with a large number of lights fast, but we could also apply the photon mapping techniques of HW3, augmented with the optimization described in the SIGGRAPH 2002 course 43 on Photon mapping.
Guillaume will focus mainly on the modeling of the trees and the global illumination, and Pramod will look at modeling the snow and adding the translucency effect.