Résumé
High compression of plant geometry is an important aspect in fast realistic visualization of plants. Hierarchical structuring plant morphology is a key factor for real time plant rendering, especially when pedestrian views, including both close-ups and far views, are requested. We present here a new geometric simplification method, called View-dependent Hierarchical Foliage Simplification (VHFS). It aims to construct efficient multi-resolution models, faithful to botanical knowledge for sparse organs of trees, such as leaves, flowers and fruits. Both preprocessing and view-dependent rendering processes are considered hereby. In the preprocessing phase, sparse organs are simplified hierarchically with respect to the topological structure of the plant, i.e. to the plant branching order hierarchy and the phyllotaxy (or anthotaxy) groups. In the rendering phase, the simplification degrees for organs in different locations in the crown are defined from the current viewpoint. The selection of the different simplification levels is based on the distance to the viewer and a visibility coefficient of the considered organs. This visibility coefficient is an approximate occlusion based on the relationship between the viewing direction and direction of each first order branch. Compared with other foliage simplification methods, the main advantages of VHFS lay in the respect of consistent botanical structure at any stage of compression, ensuring realistic foliage appearance, higher efficiency in preprocessing stage and higher data compression.