Data And Rules-Driven Synthetic Of Three-Dimensional Modeling Of Trees

One of the goals of Virtual Geographic Environments(VGEs)is to simulate and analyse the complex geographic processes and phenomena based on computer hardware and software conditions,to help solve the geographical problems.Forest is a major component of the geographic environment.Accordingly,one of the ultimate goals of the virtual plant is to assist in the analysis and prediction of plant ecosystem.Detailed,precise and objective plant morphological structure model is the foundation of the virtual plant deep studies,e.g.,quantitative simulation of interaction between plants and environment,biomass estimation.In order to establish an accurate 3D tree model,this paper take loquat trees with different crown shape as examples.Combing the advantages of rule-based modeling method and data-based modeling method to develop the research on 3D tree modeling.The specific content and achievements of this paper are as follows:(1)We take a field investigation on loquat trees which located in Fuzhou Loquat Resource Nurseries of National Fruit Gene-Pool and loquat production base in Yunxiao county of Fujian province,and capture loquats,morphological structure information and point cloud data of leaves,fruits and trees by hand-held laser scanner Artec Eva,Riegl VZ400 terrestrial laser scanner and measuring tools of the morphological structure.(2)Because a single plant modeling method is difficult to accurately express the morphological structure of the plant canopy.In order to solve this problem,this paper proposes a novel strategy for integrating rule-based modeling method for generating main branch system and data-driven model methods for reconstruction of partial organs.The approach combined the advantages both rule-based modeling for presentation topological information and data-based modeling with high precision and high resolution 3D information.Using the idea of disassembly to divide the tree into the main branch system and canopy local components,and these two parts will use different modeling method.For the branch system modeling,generate the 3D model of main branch structure system based on rule-based modeling method.For the partial componment of canopy modeling,generate the precise 3D model of local components of canopy based on point cloud data.At last,using the rule-based modeling method to integrate models of partial components and branches system to generate the whole 3D tree model according to topological and geometrical constraints of their mutual connections.Taking four different types of crown loquat trees as examples,building the fine 3D tree models,we analysis the similarity of the virtual models comparied with real plants from four kinds of morphological structure factors which including crown,tree height,canopy thickness and cross-sectional area.,the results show that the virtual loquat tree model based on this method is of high precision.In the aspect of visualization,compared the modeling tree with the point cloud data,it can be concluded that the virtual loquat tree model based on this method is of high precision.(3)With the increase of the accuracy of the model,the number of the model grids are often increasing,which leads to the increase of the amount of calculation in the application of the model,and limits the application of the model.The modeling tree model based on the method proposed by this paper,the increasing surface elements are mainly distributed in the canopy local components,which affect the efficiency of the simulation of light distribution in the canopy.Because of this,a new method which was a suitable mesh simplification of blade model based on method of edge collapse was proposed.On the base of QEM simplification algorithm,a method of changing the order of edge collapses in the simplification is presented by introducing the curvature change and irregular triangle judgment into the error metrics,using half-edge collapse to keep blade model boundary.Taking the single loquat leaf and a cluster of loquat leaves as examples,and using the simplified method of this paper to simplify the leaf model.we take Hausdorff distance and the value of PAR of virtual canopy for accuracy analysis,the experimental results show that the simplified model can keep the main morphological structure characteristics of blades and get a well visualization effect,and improve the calculation efficiency of radiation simulation significantly.