Strands, Gravity and Botanical Tree Imagery

Abstract

This paper presents a technique for the modelling and rendering of realistic botanical tree images. A strand model is used that is analogous to the internal vascular structure of a tree. The model is"grown" under the simulated influence of gravity and light. The strand densities at each branching point are used to determine branching angles, branch lengths and branch thicknesses, taking into account stored, user definable parameters that characterize the species of tree being modelled. These parameters address such factors as gravimorphism, phototropism, orthotropism, plagiotropism, planartropism and phyllotaxis, and are distributed according to a branch ordering system.Branch segments and joints are modelled by Bezier splines, with an assumed circular cross-section. Leaves are made up from numbers of sample ranges from vector plane equations. The trees are rendered using a surface sampling algorithm with a light Z buffer for shadows and autoregression textures for tree bark and grass.