Représentation et rendu multi échelle d’arbres réalistes pour la synthèse de paysages naturels

Abstract

This report concern the representation of trees for high quality landscapes rendering dedicated to the realistic representation of forest conifers. The main characteristic of a natural landscape is its complexity, in all senses of the term. A landscape is a vast land for the scientific observer where of the thousands of phenomena interacts between them to give a qualitative and quantitative wealth of shapes, of movements, of colors, etc. Like all scene a stage of landscape requires a phase of modelling of the factor there taking room, mainly the land and trees. Techniques of tree modelling give good results in terms of diversity of species and shapes. However, the multitude of polygons of their geometrical representations generates a high computing cost an important problems of aliasing at rendering. Mesh simplification in order to built level of details is not adapted to trees since is alters global illumination and opacity, because of the discontinuous repartition of the leaves. With the idea of representing groups of primitives (leaves) using packets combining geometric and photometric appearance. Using the knowledge of the geometric distribution of needles, we use a representation based on the analytical computation global illumination model of the geometric branch of needles. In this case, we compute an analytical a hierarchy of three shaders able to represent effect of lower levels, without sampling and with self shadowing and visibility. The analytical aspect of these shaders allows in the same time the acceleration of computing time and good image quality, particularly with little aliasing.