【作者】 李勃；

【导师】 陈戈；

【作者基本信息】 中国海洋大学 ， 地图学与地理信息系统， 2013， 博士

【摘要】 海洋是一个巨大复杂、各种因素相互影响，多类过程彼此作用的时变系统。中国是一个海洋大国，社会和经济发展必然越来越多地依赖海洋。数字海洋是由海量、多分辨率、多时相、多类型海洋监测监视数据及其分析算法构建而成的海洋信息系统。从国家发展战略的高度出发，我国将数字海洋列入国家海洋科学技术发展计划。随着这一发展目标的确定和实施，运用数字化手段统一处理和表现海洋数据和现象已成为迫切需要解决的重大课题。本文设计了面向数字海洋应用的虚拟海洋三维可视化仿真引擎(Virtual-Reality and Visualization Engine of Ocean)—i4Ocean，其中“i4”代表虚拟海洋可视化仿真的浸没感（Immersion）、交互性（Interactivity）、构想性（Imagination）和智慧性（Intelligence）。引擎不借助其它地理信息系统软件的二次开发功能，全部基于底层开发，具有自主知识产权。另外，引擎除了界面交互部分的实现借助于MFC类库之外，其他全部功能都不依赖MFC开发环境，便于引擎的跨平台和跨系统交互。i4Ocean为海洋数据的管理提供了一种海洋时空数据模型支持，该模型能很好的描述和存储海洋时空数据和特征数据。引擎使用可编程特效文件来管理和实现海洋中复杂的光影效果和可视化效果。i4Ocean包含资源管理、场景管理、渲染管理和交互管理四大功能模块，为用户和开发者提供实时交互的三维海洋虚拟环境搭建，海洋数据可视化等基本功能。用户和开发者可以基于引擎快速方便的搭建海洋平台，并扩展和增加自己的功能。最后基于引擎模拟了海上溢油现象，实现在海面风场和水下流场的影响下，油粒子扩散、漂移全过程；并搭建了海洋水文环境要素可视化系统，实现了中国东海水文环境数据球面三维体绘制和三维矢量场可视化。本文的主要贡献有：（1）设计和实现了虚拟海洋与三维可视化仿真引擎—i4Ocean。本文采用模型-视图-适配器-特效（Model-View-Adapter-Effect）框架模式搭建引擎底层架构，进行界面、交互、功能和特效的封装。上述四个部分之间的联系弱化，实现了弱耦合的关系，视图层和功能层分离，允许更改视图层代码而不用重新编译模型和适配器代码。同时引擎为开发者提供了数据、交互、功能和特效的扩展接口，以便增加新的数据、功能和特效。i4Ocean封装和实现了海洋可视化仿真功能模块，用户和开发者可以基于引擎快速搭建三维海洋可视化仿真平台。（2）提出了适合海洋数据的球面体绘制方法。传统的光线投射体绘制算法在长方体中实现，对于虚拟球体场景中的海洋体数据可视化，长方体渲染结果不能精确定位在地球表面位置；由于地球曲率的影响，对于大范围海洋数据，该方法的绘制结果的误差也是非常大的。本文提出了一种GPU加速的球面体绘制方法，在坐标系转换过程中采用了球体坐标系，海洋数据在球壳体中绘制能够更好体现表达海洋数据的形态和变化。（3）提出了自适应噪声采样的三维矢量场体绘制方法。传统的线积分卷积（LIC）选择噪声纹理作为输入，通过线积分卷积矢量数据得到输出流线纹理的每个像素值，这种方法使用固定空间分辨率的噪声纹理，采样频率不随视点距离远近发生改变。本文提出一种根据视点距离，自适应设置采样分辨率，实时生成新的噪声纹理送入GPU中进行流线卷积生成，实现一种随视点距离远近变化，绘制流线也随之减增的多层次细节（LOD）的效果。更多还原

【Abstract】 Ocean is a complicated dynamic time-varying system with many factors andprocesses interacting. China is a large maritime country and increasinglydependents on the ocean because of the development of society and economy."Digital Ocean" is an ocean information system consisting of vast,multi-resolution, multi-time phase, multi-type data and its correspondingalgorithm. China has already put “Digital Ocean” into the developmentprogramme of marine science and technology as a long-term strategy. As theproceeding of this programme, the task of digitalized management, analysis andexpression of marine data has become increasingly pressing.In this paper, a virtual-reality and3D-visualization engine of ocean, i4Ocean,is designed for the applications oriented to “Digital Ocean”. The word i4means4Is:“Immersion”,”Interactivity”,”Imagination” and”Intelligence”. i4Oceanprovides a marine space-time data model for marine data management. Thismodel can well express marine space-time data and somecharacteristic patterns.The engine of this model employs the programmable effect files to manage andrealize the complicated visualization effects such as shadows. i4Ocean contains4main modules, which correspond4different functions of management. They areresource management module, scene management module, renderingmanagement module and interactivity management module. They can help usersand developers to build a real-time interactive3D environment of virtual oceanand realize the basic functions of marine data visualization. Based on this engine,users and developers can also build an ocean digital platform efficiently andextend their functions for some special use. In the last, two application cases arerealized based on this engine. The first case is the simulation of oil spilling in theocean. In this case, the whole diffusing and drifting process of the oil particlesunder the influences of wind and flow field is emulated and visualized. The other case is constructing a visualization system of hydrologic environment. And in thiscase, this system realizes the spherical3D visualization of scalar and vector datalocated at Chinese East Sea.The main contributions of this paper are:1. Design and realization of a virtual-reality and3D-visualization engine ofocean, i4Ocean. In this paper, an improved Model-View-Adapter-Effect frame isemployed to build the underlying architecture of the engine so that the integrationof interface, interactivity, function and effect is realized. The connections amongthese4parts are reduced, which realizes the weak coupling. The layers of viewand operation are isolated, so the codes in view layer can be edited withoutre-compiling codes of model and adapter. Meanwhile, the engine providesexpanded ports of data, interactivity, function and effect for developers. i4Oceanpackages and realizes the visualization and emulation of the ocean. Base on thisengine, users and developers can also build digital ocean platforms of differenttypes efficiently.2. A sphere-based volume rendering method, which is suitable for theexpression of ocean data, is proposed. The traditional ray-casting method ofvolume rendering is realized in a cube. However, for topographic data of largespatial scale, cube-based volume rendering cannot precisely reveal the geographicposition on the earth because of the influence of the earth’s curvature. So it willcause a lot error when displaying large-scale oceanic data. In GPU-acceleratingsphere-based volume rendering method, spheroidal coordinates are employed inthe process of coordinate transformation. Volume rendering in a sphere can betterexpress patterns and variations of marine data.3. A self-adapting noise-sampling volume rendering method of vector data isput forward. The traditional Line Integral Convolution (LIC) method selects thenoise texture as the input, and uses line integral to convolute the output data.Then every value of pixel of the output texture can be obtained. This method usesthe noise texture with a fixed spatial resolution and the sampling frequency of thismethod is also fixed regardless of the distance of the view point. In this paper, a self-adapting method of setting sampling resolution considering the distance ofthe view point is used. The new real-time noise texture is sent to GPU forgenerating the convolution of flow line. Using this method, a Level-Of-Detail(LOD) effect, the amount of the flow line vitiating with the distance of the viewpoint, is realized.更多还原