Modeling and animation of botanical trees for interactive virtual environments

This paper proposes a new modeling and animation method of botanical tree for interactive virtual environment. Some studies of botanical tree modeling have been based on the Growth Model, which can construct a very natural tree structure. However, this model makes it difficult to predict the final form of tree from given parameters; that is, if an objective form of a tree is given and it is to be reconstructed into a three-dimensional model, we have to change the parameters to reflect the structure by a trial-and-error technique. Thus, we propose a new top-down approach in which a tree's form is defined by volume data that is made from a captured real image set, and the branch structure is realized by simple branching rules. The tree model is described as a set of connected branch segments, and leaf models that consist of leaves and twigs that are attached to the branch segments. To animate the botanical trees, dynamics simulation is performed on the branch segments in two phases. In the first phase, each segment is assumed to be a rigid stick with a fixed end on one side, and rotational movements from influence of external forces are calculated in each segment independently. And the forces propagated from the tip of a branch to the root are calculated from the restoration force and thickness of the branch. Finally, the rotational movements of segments are executed in order from the base segment, and the fixed end of each segment is moved to the free end of the segment to be connected so as to maintain the relative angles between the segments. The proposed model is applied to many kind of botanical trees, and the model can successfully animate tree movements caused by external forces such as winds and human interaction to the branches.