| Virtual trees 3D trees modeling,visualization and immersive virtual scene have been the research focuse in virtual reality technology and agricultural informatization.Steady image quality,realistic scene,the body induction interaction,the continuity of changing environment and social contact and etc.are the main factors influencing the immersion in the wearable VR divice.Because of the lack of enough immersion with low simulation precision model in the traditional virtual reality,the effectiveness of trees visualization is unreal.Traditional modeling of trees based on the rules or images could not satisfy the requirements of simulation in virtual scene.To provide a realistic tree model,a point-based tree modeling approach is employed to reconstruct the tree model.In this thesis,we implement a VR system based on wearable devices with realistic model and virtual scene.The main research contents of this thesis are as follows:(1)3D tree reconstruction.To generate more accurate tree models for virtual scene,a tree reconstruction approach has been implemented using point-cloud as input.Firstly,the tree skeleton has been generated by Space Colonization Algorithm.Then,the tree has been drawn through generalized cylinder and Pipeline model method.After that,the tree model has been exported to OBJ file.Secondly,the model file has been imported into Unity.And adding the trees with realistic texture based on PBR Mode and shaders,the shadow of scene has been set up the real-time lighting mode with global light of per-pixel processing.Finally,tree visualization of this thesis has been highly immersive and realistic.(2)The immersive virtual scenes of tree visualization is based on Oculus and Unity.Due to differences in the display equipment and the way of observation,VR roaming and the associated equipment use wearable devices of Oculus and the VR camera use Oculus SDK.The main contents includes camera motion,correlation tracker,transformation and rendering.All of these has provided six freedom degrees of impression for users.The scene of collision detection is based on improved sphere bounding box algorithm,which can exclude impossible collision object to decrease detection operation,and combine with the method by saving resources of judgement to set collider for the effective collision zone of trees.It can improve the efficiency of collision.The construction of virtual scene is considered as a measure to enhance the sense of immersion which involves sky,mountain range,water and static vegetation.The sky box is bound to the camera.The Terrain Engine is used to generate irregular bump terrain.The naturalscene use mixed texture mapping to simulate mountain range.The water surface simulation is based on the projected grid.The simulation of wave use the Gerstner wave,which is applied to the water in Unity.It constructed static vegetation through 3ds Max tools and Billboard principles.(3)System optimization and test.In this thesis,some techniques are adopted in the virtual reality system: DS rendering pipeline has been proposed to reduce the cost of the illumination calculation,culling techniques have been used to reserve the resource of rendering and the LOD technology has been used to simplify the complexity of remote model,which can optimize the calculation ability of the system with multi-model.All of the methods proposed above can make the system run smoothly.In the end,we use the black box testing and the experiencing system of volunteer to count the feedback data.Compared with the displaying method in traditional VR,the tested results show that our system can reach 60 FPS.The questionnaire reveals that the prefect rate is 70% and excellent rate is near to 30%.The realistic intensity feedback of the models and scene shows that the prefect rate is 52.5% and excellent rate is nearly 17.5%.The outstanding rate of trees visualization immersion is 45% and the rate of excellent is nearly45%.Based on above processes,the implemented immersive system can satisfy the expected requirements in function and performance. |
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