本文選題：樹木可視化　切入點：虛擬現(xiàn)實技術(shù)　出處：《西北農(nóng)林科技大學(xué)》2017年碩士論文

【摘要】：虛擬樹木三維形態(tài)構(gòu)建研究、樹木可視化和沉浸式虛擬場景的構(gòu)建是當(dāng)前虛擬現(xiàn)實技術(shù)與農(nóng)業(yè)信息化領(lǐng)域的研究熱點和重點。穿戴式VR體驗中穩(wěn)定的圖像質(zhì)量、場景真實感、身體感應(yīng)交互、環(huán)境變化連續(xù)性和社交等是影響沉浸感的主要因素。目前傳統(tǒng)虛擬現(xiàn)實展示所帶來的沉浸感有限,相關(guān)內(nèi)容體驗不夠真實、模型不夠仿真精細,樹木可視化的效果不佳。基于規(guī)則與基于圖像的方法存在操作復(fù)雜度較高,模型未能較好的達到仿真要求等問題,不能滿足本研究的需求。為了改善以上問題,特使用真實樹木點云三維數(shù)據(jù),提高樹木可視化的精細度。本文從模型重建、虛擬場景構(gòu)建以及可穿戴式設(shè)備方面研究并實現(xiàn)一種實現(xiàn)虛擬現(xiàn)實系統(tǒng)的方法,主要的研究內(nèi)容如下:(1)重建三維樹木。針對樹木模型構(gòu)建不精確,不自然的問題,樹木可視化工作基于三維激光點云結(jié)構(gòu)模型的方法對樹木進行重建。主要包括以下步驟:首先,利用點云數(shù)據(jù),通過空間殖民算法生成樹木骨架,對骨架使用廣義圓柱體和管道模型原理繪制樹木。其次,樹木模型根據(jù)OBJ格式語法生成模型文件,使用Unity讀取文件獲得樹木模型。樹木材質(zhì)通過PBR渲染模式與著色器生成,場景陰影的渲染使用逐像素處理的全局光實時照明模式。最后,本文的樹木可視化具有高度的真實感、沉浸感效果。(2)基于Oculus與Unity的樹木可視化沉浸式虛擬場景。由于顯示設(shè)備和觀察方式不同,VR漫游與相關(guān)設(shè)備關(guān)聯(lián)使用Oculus VR設(shè)備,VR攝像機通過Oculus SDK開發(fā)。其主要內(nèi)容包括攝像機運動、關(guān)聯(lián)跟蹤器、變換和渲染,可為使用者提供六自由度的觀察體驗。場景碰撞檢測以改進的球形包圍盒算法為基礎(chǔ),快速排除不可能碰撞的物體,再結(jié)合節(jié)省判斷資源的方法,對樹木主干的有效碰撞區(qū)域設(shè)置碰撞器,提升碰撞檢測的效率。虛擬場景的搭建作為提升沉浸感的輔助措施,其中涉及到:天空、地面山脈、水面和靜態(tài)植被。天空盒綁定攝像機,地面與山脈使用Terrain Engine和貼圖復(fù)合。水體模擬使用投影網(wǎng)格和Gerstner波,靜態(tài)植被通過3Ds max工具和Billboard原理構(gòu)造。(3)系統(tǒng)優(yōu)化與測試。本文通過對虛擬現(xiàn)實系統(tǒng)采用:DS管線渲染降低光照計算開銷,剔除技術(shù)節(jié)省渲染資源以及LOD技術(shù)簡化遠距離模型的復(fù)雜度等方法優(yōu)化多模型情況下系統(tǒng)的計算能力,從而保持系統(tǒng)流暢運行。本文最后使用功能用例的黑盒測試、志愿者系統(tǒng)體驗等調(diào)查方式,統(tǒng)計反饋數(shù)據(jù)。與傳統(tǒng)的VR展示方式對比,本虛擬現(xiàn)實系統(tǒng)測試結(jié)果表明:可達60FPS的較優(yōu)流暢度,優(yōu)秀率為70%,非常優(yōu)秀率近30%;模型場景真實感反饋優(yōu)秀率約為52.5%,非常優(yōu)秀率近17.5%;樹木可視化沉浸感體驗優(yōu)秀率為45%,非常優(yōu)秀率近45%。通過以上結(jié)論判定,本文研究并實現(xiàn)的沉浸式系統(tǒng)可以滿足課題預(yù)期的功能和性能要求。
[Abstract]:The research of virtual tree 3D shape construction, tree visualization and immersive virtual scene construction is the focus of research in the field of virtual reality technology and agricultural informatization. The image quality and scene reality in wearable VR experience are stable. Physical interaction, environmental continuity and social interaction are the main factors that affect immersion. At present, the traditional virtual reality display brings limited immersion, the related content experience is not real enough, the model is not accurate enough. The performance of tree visualization is not good. The rules based and image-based methods have some problems such as high operation complexity, the model can not meet the requirements of simulation, and can not meet the needs of this study. In this paper, we study and implement a method to realize virtual reality system from the aspects of model reconstruction, virtual scene construction and wearable devices. The main contents of the study are as follows: (1) Reconstruction of three-dimensional trees. Aiming at the imprecise and unnatural construction of tree models, Tree visualization is based on the 3D laser point cloud structure model, which includes the following steps: firstly, the tree skeleton is generated by using point cloud data and spatial colonization algorithm. Secondly, the tree model generates the model file according to the syntax of OBJ format, and uses Unity to read the file to obtain the tree model. The tree material is generated by PBR rendering mode and shader. The rendering of the shadow of the scene uses the global light real-time illumination mode which is processed by pixel by pixel. Finally, the tree visualization in this paper has a high degree of realism. Immersive effect. 2) based on Oculus and Unity, the visual immersive virtual scene of trees. The main content of the virtual scene is developed by Oculus SDK because of the different display devices and different viewing ways. The Oculus VR camera is developed by Oculus SDK. Including camera motion, Correlation tracker, transform and render, can provide the user with six degrees of freedom observation experience. Scene collision detection is based on the improved spherical bounding box algorithm, which can quickly eliminate objects that can not collide, and combine with the method of saving judgment resources. To improve the efficiency of collision detection by setting up collider in the effective impact area of tree trunk. The virtual scene is used as an auxiliary measure to enhance immersion, which involves: sky, mountain range on the ground, Water surface and static vegetation. Sky box binds camera. Ground and mountain use Terrain Engine and map composite. Water simulation uses projected grids and Gerstner waves. Static vegetation is optimized and tested by using 3Ds max tool and Billboard principle. Culling technology saves rendering resources and LOD technology simplifies the complexity of remote models to optimize the computing power of the system in the case of multiple models, so as to keep the system running smoothly. Finally, this paper uses the black box test of functional use cases. Compared with the traditional VR display method, the virtual reality system test results show that the optimal fluency of 60FPS can be achieved. The rate of excellence is 70, the rate of very good is nearly 30; the rate of model scene truthfulness feedback is about 52.5, and the rate of very excellent is nearly 17.5. the excellent rate of visual immersive experience of trees is 45, and the rate of very excellent is nearly 45.According to the above conclusions, The immersion system studied and implemented in this paper can meet the expected functional and performance requirements.
【學(xué)位授予單位】：西北農(nóng)林科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：S758;TP391.9

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