A ray density estimation approach to take into account environment illumination in plant growth simulation
Light interaction is one of the most important factors in developing realistic plant models. Plants react to received illumination by bending branches, adapting their growth rate, orienting leaves and flowers, producing larger or smaller leaves, etc.
 In this paper, we present a novel approach to simulate plant growth as a response to environment illumination. The basic idea of our algorithm is to simulate light transport in the environment in which plants grow by tracing light particles originating from light sources. Both intensity and mean direction of incident illumination are determined easily. This is based on a ray density estimation of the environment illumination by means of a predominant illumination direction.
 An adaptive spatial data structure is used to store the rays along which light particles travel in space. This data structure allows efficient calculation of ray density at locations where the algorithm needs to query incident illumination.
 Our approach takes into account both direct and indirect illumination and is an algorithm that is both flexible and accurate. It is easy to implement and more general illumination models can be incorporated in a straightforward manner. Furthermore, using a non-uniform, adaptive data structure for storing the rays, calculation time and storage requirements are kept within reasonable limits.