Trees

This demonstration shows a method for accelerating the realistic rendering in ray-tracing of forests of pine-trees.
As for many complex materials (hair, fur, fabric, cristals), pine-tree needles have an effect in the tree illumination even if their small size seems to be geometrically neglectable.
The classical level of detail approaches consisting in replacing several small entities by a large single one thus destroy important information. The contribution of each needle should not be lost, but at the same time, dealing with each of the billion of needles of the scene individually is not affordable and would yield an untractable rendering time and a strong aliasing.

Our approach consists in derivating reflectance functions, or shaders, which analytically integrates the luminous contributions (reflects, shadows, opacity) of a set of needles. Depending of the distance, this `set' corresponds to one needle, a cone of needles, or a whole branch. This corresponds to three different levels of details, which have the same behavior as a bough of needles.

We can now compute very complex scenes like the one below (~10 000 000 needles). Using cone tracing algorithm, computation time decreases dramatically to approximately 10 minutes, that's to say ten times quicker than classical ray-tracing systems, with a better image quality.

For further details: http://www-evasion.imag.fr/Publications/2000/MN00/
Contacts: Alexandre.Meyer@imag.fr - Fabrice.Neyret@imag.fr