摘要
采用L系统结合野外观测数据来构建植被单体的三维结构模型,根据植被模型特点,分别对枝干和树叶两个组成部分进行几何简化,大幅度减少模型所需的几何要素数量。在冠层模型简化中,提出了分层LOD模型提取方法,该方法可以高效提取出多复杂度的冠层LOD模型,同时保证组成LOD模型的每片叶子都符合最小化误差方程的要求。在实时渲染过程中,依据LOD技术对大规模植被实时可视化。为了实时得到植被在动态LOD场景中所需要的复杂度,提出了一套LOD植被模型调用的新标准:用衰减因子描述植被密度和视距对植被细节程度衰减的影响,为动态LOD场景提供连续变化的复杂度标准。
This paper addresses an approach for dynamic and continuous multi-resolution visualization of large forests.Firstly,the approach uses the L-systems to generate 3D tree models,which are composed of two kinds of geometric elements: branches and leaves.The plants are simplified respectively to multi-resolution models of branches and foliage by our method.Secondly,the approach quantifies the resolution of LOD models by the length of branches and the quantity of foliage.The branch length for the branch LOD model and the leaf quantity for the foliage LOD model are obtained by the decay factor.Taking the values as the criterion,we extract LOD models from the multi-resolution models of branches and foliage in real time.Finally,we render the forest scene.This paper presents a continuous LOD rendering for forest landscape,and the main originalities of our method are summarized as follows.(1) To improve the efficiency for extracting the continuous LOD models,the multi-resolution chains and the binary tree structures are established respectively for the branches and the crowns,both of which consist of the preliminary models of the tree.(2) Our method for generating crown LOD models here shows that,they can implement large forest scene real-time visualization.(3) This paper makes new criteria for the LOD models,which use the decay factor to act on the original branch length and the original leaf quantity.In this way,the levels for displaying trunk and branches are calculated.This method is applicable to all kinds of plants with strong universality and practicability.So how to simplify crowns of such kind of trees is another important research subject.In future work,we should combine geometry-based and image-based simplification methods to further speed up visualization of large plant scenes.
出处
《地理研究》
CSSCI
CSCD
北大核心
2012年第3期565-577,共13页
Geographical Research
基金
中国气象局小型基建项目(200110804)
中国气象局关键技术项目(CMAGJ2011M64)
国家发改委项目(JCXXK-HT2009-017-02)
公益性行业(气象)科研专项(GYHY(QX)2007-6-7)
关键词
L系统植被
动态LOD
几何简化
森林场景
L system vegetation
dynamic LOD
geometrical simplification
forest scene