Abstract: A computer-based method for generating vegetation such as 3D models of trees. The method includes providing in memory a template with model growth rules. A computer processor positions a seed particle in a location in digital 3D space. The base particle is associated with a set of attributes stored in the memory, such as attributes or values provided in the template. A generator module generates the tree model (e.g. a particle system) using a particle-based growth process starting with the seed. The particle growth includes iteratively generating additional particles and also includes gathering environmental data regarding the 3D space for the particles. Then, the method includes determining a move direction for each particle based on the growth rules evaluated with the environmental data The particles are moved to new positions using the move direction, and these steps are continued through time steps to create the tree model.