The Study Of Visual Simulation Technique For Large-scale Forest Landscape

In our vast country,forest resources including foreste types, area and forest stock wereabundant in the world. Most forest informationcould be derived from the national forest inventory(NFI), but detailed distribution and quality of forest were not available. So methods for reflecting the forest distribution condition intuitively was required.Forest landscape visualization wasnewly arisen technique that not only showedthe forest structure and distribution feature clealy but also revealedthe reflections from plants diseases and insect pests and the indications on the forest change and management, further on internal rule could be concluded from the ruleless forest scene to support the forest scene planning and forest management efficiently.Forest landscape visualization wasuseful but there weretwo problems in creating large scenes. First, huge memory space and peripheral storage was taken up by a large forest landscape data volume due to millions of trees and countless scenes. Second, to realize the real-time rendering and dynamic simulating on a large forest scene containedtens of millions triangles, which demanded for advanced software and hardware but it is unachievable now.In order to solve the problems, a method wasexpounded for simulating and optimizing the large forest landscape based on GPU and realizing the designation of the system. With apractical platform, forest scene was established quickly and simulated visualisation interactively meanwhile a digital forest was constructed and managed. The own created platform was used to perform 3D interactive processes.On the whole, contributions of this study were concluded in threepoints below:(1) Single tree real-time rendering and optimal exhibition techniqueFirstly, the study developed a method for performing sigle tree diversification based on tree model splited and gridding mask.Tree model was used as unit to construct the forest scene, and organization and complexity of the tree model were both related to real-time rendering efficiency of the large forest landscape. Secondly, by improving the existing researches,tree structure with modified IFS system was built and crown structure withsimplified simple curve model was built in the study. Thirdly, with observation of sigle tree in forest farm, tree model was composed of tree trunk, tree branches and leaves andmodel mask code was used to mark each partial model for creating the sub-model libraries of each tree specie. The sub-model contained independent structure and texture LOD of each one, which enhanced level details and the visualisation of sigle tree. Various tree styles were emerged by random combination of the mask code while sigle tree rendered. To accelerate real-time rendering of sigle tree, compsiting figure with image produced the optimal processing for the furthest tree.(2) Large landscape management besed on improved landscape theoryLinear traversal wasted the system time and decreased the system utility and operability due to huge data size and plentiful entity objects, so the entity objects in the scene should be planned and managed when rendering. In addition, the study indicated that the large forest landscape type was a complexity of static and dynamic scene. With analysis of scene graph and octree theory, design of management on large scene improved by programming was used by SceneNode related to OctreeNode inheriting, so that the OctreeNode performed not only the spatial distrbution but also the real hierarchy of the scene inherited. The improved scene graph theory implementedefficient management of static and dynamic entity in large scene at the same time that decreases the CPU occupation of entity traversal and acceleratedthe interactive visualization operation in 3D scene.(3)Large forest landscape real-time rendering and dynamic simulation techniqueTo achieve agoal of large forest landscape real-time rendering by sigle tree rendered simultaneously, atechnique based on hardware instantiation and the vertex texture collection was developed in the study, which was derived from entity technique, memory usage, CPU load and technical suitability. Instantiated tree trunk、branch and leaves by instantiation was randomly combined to form the effecient generation of verious tree entities in rendering. To realize forest landscape dynamic simulation, a texture was created from bone information of all entities by the vertex texture collection technique, then the right bone was choosen for the corresponding entity, performing the entity animation function which the hardware instantiation did not possess. The good performance of the instantiation demonstrates that hardware instantiation and vertex texture collection techique chould reduce the memory usage and CPU load.(4) Implement visualization system of large forest landscapeCombining the above studies and practice, anoriginal visualization system of large forest landscape was constructed in terms of the function module, property and structure analysis.Guozigou forest farm in Huocheng of Xinjiang was usedasstudy area where 3D visualisation simulaiton in foreat landscape was realized and whosearea wasover 300 km2,containing twomillions scenes.The own created platform was used to perform the 3D interactive processes, such as forest wandering, subcompartments attributionn indexing, serching, recording and modification, total average frame rate was more than 20 FPS that couldmeetappliacation.requirements.Designation and experiment of large forest landscape visualisation simulaiton technique that mentioned above could used as a feasible case for digital forest and forest management.