树的表达无论是在3DGIS，VRGIS还是在3DCM中，都是一个难点问题。与一般实体对象不同的是，树明显具有分形空间特征，因此用常规简单的建模方法很难表达一颗树。现在分形算法常用来生成树模型，具有逼真的可视效果，但所产生的数据量对于GIS环境来说太大，可视化困难；另外，用树的图像替代树模型也是一种常用的方法，但在近视点视觉效果差，同时也没有表达出树木所固有的空间特征。本文作者提出一种方法，使用LOD技术，将树的分形模型与其图像替代模型两者结合起来，初步解决树模型在GIS中的可视化问题，可达到逼真、高速的可视效果。

The 3 dimensional visualization of a tree model is a difficult problem,especially in GIS field Spatial characters of trees have great differences from common objects It has clear fractal character,and it's difficult to establish data model using common modeling methods Now,fractal theory is in use widely,and it could produce vivid effect However,the data amount is very large for 3 dimensional visualization in GIS Tree image is used more widely than that of tree model,but in the near viewpoint,tree image would have a bad effect because the essential characteristics of a tree are ignored in this way In this paper,the advantages of the modeling and Level of Detial(LOD)technology have been used Our modeling scheme is to use a tree 3D model produced from fractal algorithms This model is managed by BLOB type in database because it is difficult to do spatial analysis using fractal model One cuboid could envelope a tree model in spatial analysis process and in visualization process Tree fractal model could only be used in very near viewpoint Multi solution tree images are used to express trees in different view distances Theses images are also managed using BLOB data types in database Same cuboid in fractal model is also used in spatial analysis Fractal tree model and multi solution tree images are combined by a fix LOD division in visualization process according to system design or user selection LOD division is referred to view distance and tree images solution At the end of the paper,our experiment system is introduced It shows that our method could be used to solve 3 dimensional visualization in city environment in tree model,and have a good effect