Multiresolution foliage for forest rendering

Plants are important objects in virtual environments. High complexity of shape structure is found in plant communities. Level of detail (LOD) of plant geometric models becomes important for interactive forest rendering. We emphasize three major problems in current research: the time consumption in LOD model construction and extraction, the balance between visual effect and data compression, and the time consumption in the communication between Central Processing Unit (CPU) and Graphics Processing Unit (GPU). We present a new foliage simplification framework for LOD model and forest rendering. By an uneven subdivision of the tree crown volume, the cost for LOD model construction is drastically reduced. With a GPU-oriented design of LOD storage structure for foliage, the costly hierarchical traversal of a binary tree is replaced by a sequential lookup of an array. The structure also decreases the communication between the CPU and the GPU in rendering. In addition, Leaf density is introduced to adapt compression to the local distribution of leaves, so that more visually relevant details are kept. According to foliage nature (broad leaves or needles), higher compression are finally reached using mixed polygon-line models. This framework is implemented on virtual scenes of simulated trees with high detail. Copyright © 2009 John Wiley & Sons, Ltd. This framework deals with almost all kinds of leaves shapes, broad leaves and coniferous ones. Higher data compression of the crown data can be obtained with this new technique due to leaf density and the co-existence of different resolutions in a crown. This method takes advantage of the graphics hardware, so that large-scale plant scenes can be rendered interactively. A bird's eye view of a virtual forest with 7 species 22 560 trees of broad leaf and thin leaf trees. The total number of foliage polygons of the original tree models in the forest is 8.7 × 108.

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