Dynamic Visualization Simulation Technology Of Chinese Fir Stand Growth Based On Spatial Structure Characteristics

As an important part of forest management,stand growth simulation has great significance for forestry production practice.Traditional way of stand growth simulation is based on the actual situation of stand at different sites and different stages of growth.It uses mathematical methods to show the process of stand growth in the form of charts,formulas and computer programs.This method is complex,and is difficult to visualize the dynamic process of stand growth.The purpose of this study is to develop a growth simulation method considering the relationship between the spatial structure and growth of the stand by constructing a sample library of Chinese fir,and combines the three-dimensional visualization technology to realize the dynamic simulation of Chinese fir stand growth.Based on the continuous survey data of six plots of Chinese fir plantation in Huangfengqiao State-owned Forest Farm of Hunan Province from 2012 to 2017,the horizontal and vertical spatial structure parameters of stand based on spatial structure unit were established,by considering the influence of lateral extrusion and upper light cover of the adjacent wood crowns on the growth of the central tree.On this basis,the appropriate characteristic indexes were selected to construct the growth sample library of Chinese fir,and the Mahalanobis distance was used as the matching criterion between the sample library and wood in the stand to be simulated,so as to realize the simulation of the spatial structure and growth of the stand.At last,the three-dimensional model segmentation,dynamic organization,and the animation curve technology was used to realize the dynamic visualization simulation of stand growth.The main results and conclusion are as follows:(1)Based on the influence of the lateral crown extrusion and upper light occlusion of adjacent trees,the spatial structure parameters of the stand were constructed with full consideration of the natural competition.It quantitatively describe the spatial structure of wood from horizontal and vertical spatial levels.The results show that the horizontal and vertical spatial structural parameters are significantly negatively correlated with the annual growth of tree diameter at breast height(D),and the correlation coefficients are up to-0.572 and-0.581,respectively.It provides a new idea for the quantification of the spatial structure characteristics of stand.(2)Age(A),diameter at breast height,horizontal spatial structure parameters(PH),vertical spatial structure parameters(PV)and annual growth rate of D(d D/dt)were selected as characteristic indicators to construct the stand growth sample library through the analysis of influencing factors of stand growth.We simulated the changes in D and tree mortality based on the sample library.The simple linear models were used to predict the growth of the tree height(H),the crown width(CW),and the high under the living branches(UBH).The results show that the function of growth prediction of the sample library is good,and the order of prediction accuracy is D>H>CW>UBH.For stand that without management measures,the prediction accuracy of growth(R~2)of D,H,CW and UBH is 0.913,0.675,0.574,0.410,respectively.For the stand with thinning measures,the prediction accuracy of growth is slightly lower,in order 0.861,0.545,0.528,0.314.The construction of sample library provides a new idea for the study of stand growth simulation,and provides data drive for the dynamic visualization of stand growth.(3)In this study,the Unity3D engine was used as the development platform,and the growth sample library of Chinese fir was used as the data support.Based on the dynamic organization of the model and the animation curve technology,the dynamic visualization simulation system of stand growth of Chinese fir was developed.The system can run on the Immersive Virtual Reality and Visualization platform(CAVE2).The dynamic growth simulation of the DBH,H,CW and UBH of the Chinese fir stand,as well as intuitive and smooth three-dimensional visualization effect were realized in this system.That provides a visual simulation platform for forest management.