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搜索引擎-虚拟海洋与三维可视化仿真引擎的研究与开发.pdf
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IV
虚拟海洋与三维可视化仿真引擎的研究与开发
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
V
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。
关键词:数字海洋;可视化仿真;球面体绘制;3DLIC
VI
Study and Development of Virtual-Reality and
3D-Visualization Ocean Engine
Abstract
Ocean is a complicated dynamic time-varying system with many factors and
processes interacting. China is a large maritime country and increasingly
dependents 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 corresponding
algorithm. China has already put “Digital Ocean” into the development
programme of marine science and technology as a long-term strategy. As the
proceeding of this programme, the task of digitalized management, analysis and
expression of marine data has become increasingly pressing.
In this paper, a virtual-reality and 3D-visualization engine of ocean, i4Ocean,
is designed for the applications oriented to “Digital Ocean”. The word i4 means 4
Is: “Immersion”, ”Interactivity”, ”Imagination” and ”Intelligence”. i4Ocean
provides a marine space-time data model for marine data management. This
model can well express marine space-time data and somecharacteristic patterns.
The engine of this model employs the programmable effect files to manage and
realize the complicated visualization effects such as shadows. i4Ocean contains 4
main modules, which correspond 4 different functions of management. They are
resource management module, scene management module, rendering
management module and interactivity management module. They can help users
and developers to build a real-time interactive 3D environment of virtual ocean
and realize the basic functions of marine data visualization. Based on this engine,
users and developers can also build an ocean digital platform efficiently and
extend their functions for some special use. In the last, two application cases are
realized based on this engine. The first case is the simulation of oil spilling in the
ocean. In this case, the whole diffusing and drifting process of the oil particles
under the influences of wind and flow field is emulated and visualized. The other
VII
case is constructing a visualization system of hydrologic environment. And in this
case, this system realizes the spherical 3D visualization of scalar and vector data
located at Chinese East Sea.
The main contributions of this paper are:
1. Design and realization of a virtual-reality and 3D-visualization engine of
ocean, i4Ocean. In this paper, an improved Model-View-Adapter-Effect frame is
employed to build the underlying architecture of the engine so that the integration
of interface, interactivity, function and effect is realized. The connections among
these 4 parts are reduced, which realizes the weak coupling. The layers of view
and operation are isolated, so the codes in view layer can be edited without
re-compiling codes of model and adapter. Meanwhile, the engine provides
expanded ports of data, interactivity, function and effect for developers. i4Ocean
packages and realizes the visualization and emulation of the ocean. Base on this
engine, users and developers can also build digital ocean platforms of different
types efficiently.
2. A sphere-based volume rendering method, which is suitable for the
expression of ocean data, is proposed. The traditional ray-casting method of
volume rendering is realized in a cube. However, for topographic data of large
spatial scale, cube-based volume rendering cannot precisely reveal the geographic
position on the earth because of the influence of the earth’s curvature. So it will
cause a lot error when displaying large-scale oceanic data. In GPU-accelerating
sphere-based volume rendering method, spheroidal coordinates are employed in
the process of coordinate transformation. Volume rendering in a sphere can better
express patterns and variations of marine data.
3. A self-adapting noise-sampling volume rendering method of vector data is
put forward. The traditional Line Integral Convolution (LIC) method selects the
noise 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 uses
the noise texture with a fixed spatial resolution and the sampling frequency of this
method is also fixed regardless of the distance of the view point. In this paper, a
VIII
self-adapting method of setting sampling resolution considering the distance of
the view point is used. The new real-time noise texture is sent to GPU for
generating 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 view
point, is realized.
Keywords: Digital Ocean; Visualization and Simulation; Sphere-based
Volume Rendering; 3DLIC
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