基于多源空间数据的三维可视化研究
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摘要
GIS行业经过四十多年的发展,二维GIS已趋于成熟而三维GIS成为GIS新的发展趋势;计算机图形学和计算机硬件计算能力的飞速发展,为三维GIS提供了有效的技术支持;随着遥感、摄影测量等技术的应用,测绘行业在获取信息方面不论是获取信息的效率还是数量上都不断提高;另外,随着“国家基础测绘设施”项目的实施,湖北省基础地理信息数据库的建设日臻完善。基于以上理论、技术和数据的支持,实现大范围内多源空间数据的三维可视化有着重要意义。
本文在湖北省基础地理信息中心“三维地理信息漫游查询系统”项目的资助下,对多尺度、多数据源、多分辨率、无缝的海量空间数据的三维可视化方面做了深入研究,侧重解决大范围海量地形数据与实时渲染的矛盾问题。对海量地形数据的多分辨率模型设计、矢量数据的叠加、地形的三维建模、基于索引机制的地形数据块的动态调度、球体的交互操作等方面展开研究,并利用上述成果实现了三维地理信息漫游查询系统核心部分的开发。
本文的研究内容主要有以下几个方面:
1.对多分辨率LOD模型做了详细的介绍,提供了基于四叉树的LOD模型的算法。在此基础上采用球面四叉树模型对DEM数据和纹理数据进行分层、分块等预处理,从而建立起多分辨率LOD模型,采用简单明了的编码方法对预处理后的数据进行组织和存储,详细讨论了各数据块之间的拓扑关系和边界残缺数据块的处理。
2.采用地心大地坐标系,实现了基于规则格网的三维模型建立。对LOD模型各层次过度过程中出现的数据块缺少或者丢失做了有效处理。另外,采用图层的概念组织不同的数据源,对不同类型的数据源采用不同的渲染优先级,在使用过程中还可根据实际需要改变各图层渲染的先后顺序。
3.提出了将矢量数据同样采用球面四叉树的LOD模型叠加到地表。由于采用了同样的LOD模型建立规则,从而实现矢量数据与栅格数据的无缝集成,消除矢量数据叠加时出现的悬空或者陷入的现象。
4.在充分利用有限计算机资源方面,首先采用基于视景体的数据裁剪和设置图层可视域的方法减少参与建模和渲染的处理对象。另外,实现地形数据块的动态调度,通过对载入内存的数据块建立索引,当在需要载入新的地形数据块时,若内存中已载入数据块的数量达到预设值,则采用最近最久未使用置换算法(least recently used,LRU)从内存中清除最近最久未使用的数据块,然后载入新的数据块,否则直接载入数据块。
5.采用多线程程序设计的思想,将数据的载入删除、模型的建立、法方向的计算等工作作为后台线程运行,保证GaeaGlobe具有较好的交互性和实时性,及流畅的飞行、漫游和定位等操作。
6.对三维场景的动画仿真技术进行了探讨。通过对程序空闲时间的处理和更新线程的设计实现了帧动画。
7.采用四元数实现球体的旋转,研究了基于整个地球为操作对象的三维场景的漫游、缩放和线路飞行等常用功能的实现,使得GaeaGlobe具有良好的可操作性。
在上述研究工作的基础上,利用C#.NET、XML、Direct3D实现了大面积海量地形数据三维漫游查询系统的核心部分,已有的功能包括三维场景的建立、数据的加载、图层的控制、三维漫游、线路飞行、线路绘制与管理、标注的添加与管理、DLG图层中要素的查询与定位等。
由于时间有限,系统的更多功能的开发还在进行之中。但在实现项目的过程中完全利用面向对象的方法保证了系统具有良好的可扩展性,为系统的进一步完善和以后功能的扩充提供了充分的支持。随着系统的完善,对推动大范围三维地形可视化研究和湖北省基础地理信息的应用有着重要的意义。
After more than 40 years' development in the field of GIS, two-dimensional GIS has matured and three-dimensional GIS has become a new tendency of development. The rapid developments in the capabilities of computing of computer graphics and hardware provide effective technical support for three-dimensional GIS. With the application of techniques, such as remote sensing and photogrammetry, mapping industry has continuously improved both the efficiency and quantity of getting information. Besides, the implement of project named "National Basic Mapping Installation", the construction of basic geographic information data base in Hubei Province has becoming more and more perfect. On the basis of theories, techniques and data above, it has important significance to realize three-dimensional visualization of Multi-Source Geospatial Data within large area.
Being subsidized by the project named "Three-dimensional Information Roaming Inquiry System" from Hubei Geometrics Center, this thesis has made a deep research on the aspects of three-dimensional visualization of multi-scale, multi-data source, multi-resolution and seamless out-of-core Geospatial Data. Besides, this thesis made several researches on multi-resolution pattern plan of out-of-core Geospatial Data, summation of vector data, three dimension model building of landform, dynamic dispatching of landform data block based on ISAM and interactive operation of sphere, achievements of which has been made good use of to realize the development of central part of Three-dimensional Geographic Information Roaming Inquiry System
Research contents of this thesis mainly contain the following aspects:
Firstly, the author made a detailed introduction of multi-resolution LOD model and provided arithmetic of LOD model based on quadtree. On the basis of the above methods, the author also made several pretreatments on DEM data and texture data by sphere quadtree, like layering and blocking, and then set up multi-resolution LOD model. What's more, the author also adopted an easy and intelligible coding method to organize and store the data after pretreatment, and made a detailed discussion on topological relations among those block data and treatment of boundary deformity data block.
Secondly, the adoptions of geocentric coordinate system realized the construction of three-dimensional model based on Grid. During the transition course of each level of LOD model, the author made effective treatment on arisen shortage or loss of data block. In addition, different data sources were organized by layer while different kinds of sources adopted different rendering priorities. Moreover, in the process of usage, each rendering layers can be changed their orders to meet the practical need.
Thirdly, the author stated that vector data shall be overlapped to the earth's surface by the same usage of sphere quadtree. As for the use of the same LOD model foundation rule, vector data and raster data has realized seamless integration, and such kind of phenomena appeared in the course of summation were eliminated.
Fourthly, taking full advantage of limited computer resources, the author suggested adopting such kind of methods to reduce the number of objects involved in rendering and modeling, like data cutting on view frustum and layer setting on visible range. Moreover, the author also realized the dynamic dispatching of landform data block. By setting up reference for memorized data block, when needed to load new landform data block and the past memory had been default values, least recently used, LRU should be used to get rid of least recently used data block, and then new block should be loaded, or else directly loaded.
Fifthly, the author adopted multithreading programming ideology and made the following works as daemon, such as the load and delete of data and construction of model. It not only promised a better interaction and higher real-time, but also made operations fluently such as flying, roaming and positioning.
Sixthly, the author made an approach to animation technique of stimulation of three-dimensional scene. Frame-by-frame animation has been realized after coping with the free time in program and renewing the thread design.
Seventhly, the author adopted quaternion to make the sphere rotate, made researches on rendering, zooming and flying of three-dimensional scene all over the earth, which made GaeaGlobe have good operability. On the basis of researches above, the author implemented a large area data in the central part of three-dimensional rendering inquiry system by C#.NET、XML、Direct3D, existing functions including the construction of three-dimensional scene, data loading, control of layer, three-dimensional rendering, flying of circuit, drawing and management of line, accession and administration of label, inquiry and location of essentials in DLG layers.
As time is limited, development of more functions of system is also on the way. However, in the process of realizing projects, the author found that the good expandability of system was guaranteed completely depending on the mode of object-oriented, which provided full support for system's further improvement and function extension. Along with the perfection of system, it has great significance to push researches on three-dimensional visualization in large area and applications of Hubei Basic Geographic Information.
本文在湖北省基础地理信息中心“三维地理信息漫游查询系统”项目的资助下,对多尺度、多数据源、多分辨率、无缝的海量空间数据的三维可视化方面做了深入研究,侧重解决大范围海量地形数据与实时渲染的矛盾问题。对海量地形数据的多分辨率模型设计、矢量数据的叠加、地形的三维建模、基于索引机制的地形数据块的动态调度、球体的交互操作等方面展开研究,并利用上述成果实现了三维地理信息漫游查询系统核心部分的开发。
本文的研究内容主要有以下几个方面:
1.对多分辨率LOD模型做了详细的介绍,提供了基于四叉树的LOD模型的算法。在此基础上采用球面四叉树模型对DEM数据和纹理数据进行分层、分块等预处理,从而建立起多分辨率LOD模型,采用简单明了的编码方法对预处理后的数据进行组织和存储,详细讨论了各数据块之间的拓扑关系和边界残缺数据块的处理。
2.采用地心大地坐标系,实现了基于规则格网的三维模型建立。对LOD模型各层次过度过程中出现的数据块缺少或者丢失做了有效处理。另外,采用图层的概念组织不同的数据源,对不同类型的数据源采用不同的渲染优先级,在使用过程中还可根据实际需要改变各图层渲染的先后顺序。
3.提出了将矢量数据同样采用球面四叉树的LOD模型叠加到地表。由于采用了同样的LOD模型建立规则,从而实现矢量数据与栅格数据的无缝集成,消除矢量数据叠加时出现的悬空或者陷入的现象。
4.在充分利用有限计算机资源方面,首先采用基于视景体的数据裁剪和设置图层可视域的方法减少参与建模和渲染的处理对象。另外,实现地形数据块的动态调度,通过对载入内存的数据块建立索引,当在需要载入新的地形数据块时,若内存中已载入数据块的数量达到预设值,则采用最近最久未使用置换算法(least recently used,LRU)从内存中清除最近最久未使用的数据块,然后载入新的数据块,否则直接载入数据块。
5.采用多线程程序设计的思想,将数据的载入删除、模型的建立、法方向的计算等工作作为后台线程运行,保证GaeaGlobe具有较好的交互性和实时性,及流畅的飞行、漫游和定位等操作。
6.对三维场景的动画仿真技术进行了探讨。通过对程序空闲时间的处理和更新线程的设计实现了帧动画。
7.采用四元数实现球体的旋转,研究了基于整个地球为操作对象的三维场景的漫游、缩放和线路飞行等常用功能的实现,使得GaeaGlobe具有良好的可操作性。
在上述研究工作的基础上,利用C#.NET、XML、Direct3D实现了大面积海量地形数据三维漫游查询系统的核心部分,已有的功能包括三维场景的建立、数据的加载、图层的控制、三维漫游、线路飞行、线路绘制与管理、标注的添加与管理、DLG图层中要素的查询与定位等。
由于时间有限,系统的更多功能的开发还在进行之中。但在实现项目的过程中完全利用面向对象的方法保证了系统具有良好的可扩展性,为系统的进一步完善和以后功能的扩充提供了充分的支持。随着系统的完善,对推动大范围三维地形可视化研究和湖北省基础地理信息的应用有着重要的意义。
After more than 40 years' development in the field of GIS, two-dimensional GIS has matured and three-dimensional GIS has become a new tendency of development. The rapid developments in the capabilities of computing of computer graphics and hardware provide effective technical support for three-dimensional GIS. With the application of techniques, such as remote sensing and photogrammetry, mapping industry has continuously improved both the efficiency and quantity of getting information. Besides, the implement of project named "National Basic Mapping Installation", the construction of basic geographic information data base in Hubei Province has becoming more and more perfect. On the basis of theories, techniques and data above, it has important significance to realize three-dimensional visualization of Multi-Source Geospatial Data within large area.
Being subsidized by the project named "Three-dimensional Information Roaming Inquiry System" from Hubei Geometrics Center, this thesis has made a deep research on the aspects of three-dimensional visualization of multi-scale, multi-data source, multi-resolution and seamless out-of-core Geospatial Data. Besides, this thesis made several researches on multi-resolution pattern plan of out-of-core Geospatial Data, summation of vector data, three dimension model building of landform, dynamic dispatching of landform data block based on ISAM and interactive operation of sphere, achievements of which has been made good use of to realize the development of central part of Three-dimensional Geographic Information Roaming Inquiry System
Research contents of this thesis mainly contain the following aspects:
Firstly, the author made a detailed introduction of multi-resolution LOD model and provided arithmetic of LOD model based on quadtree. On the basis of the above methods, the author also made several pretreatments on DEM data and texture data by sphere quadtree, like layering and blocking, and then set up multi-resolution LOD model. What's more, the author also adopted an easy and intelligible coding method to organize and store the data after pretreatment, and made a detailed discussion on topological relations among those block data and treatment of boundary deformity data block.
Secondly, the adoptions of geocentric coordinate system realized the construction of three-dimensional model based on Grid. During the transition course of each level of LOD model, the author made effective treatment on arisen shortage or loss of data block. In addition, different data sources were organized by layer while different kinds of sources adopted different rendering priorities. Moreover, in the process of usage, each rendering layers can be changed their orders to meet the practical need.
Thirdly, the author stated that vector data shall be overlapped to the earth's surface by the same usage of sphere quadtree. As for the use of the same LOD model foundation rule, vector data and raster data has realized seamless integration, and such kind of phenomena appeared in the course of summation were eliminated.
Fourthly, taking full advantage of limited computer resources, the author suggested adopting such kind of methods to reduce the number of objects involved in rendering and modeling, like data cutting on view frustum and layer setting on visible range. Moreover, the author also realized the dynamic dispatching of landform data block. By setting up reference for memorized data block, when needed to load new landform data block and the past memory had been default values, least recently used, LRU should be used to get rid of least recently used data block, and then new block should be loaded, or else directly loaded.
Fifthly, the author adopted multithreading programming ideology and made the following works as daemon, such as the load and delete of data and construction of model. It not only promised a better interaction and higher real-time, but also made operations fluently such as flying, roaming and positioning.
Sixthly, the author made an approach to animation technique of stimulation of three-dimensional scene. Frame-by-frame animation has been realized after coping with the free time in program and renewing the thread design.
Seventhly, the author adopted quaternion to make the sphere rotate, made researches on rendering, zooming and flying of three-dimensional scene all over the earth, which made GaeaGlobe have good operability. On the basis of researches above, the author implemented a large area data in the central part of three-dimensional rendering inquiry system by C#.NET、XML、Direct3D, existing functions including the construction of three-dimensional scene, data loading, control of layer, three-dimensional rendering, flying of circuit, drawing and management of line, accession and administration of label, inquiry and location of essentials in DLG layers.
As time is limited, development of more functions of system is also on the way. However, in the process of realizing projects, the author found that the good expandability of system was guaranteed completely depending on the mode of object-oriented, which provided full support for system's further improvement and function extension. Along with the perfection of system, it has great significance to push researches on three-dimensional visualization in large area and applications of Hubei Basic Geographic Information.
引文
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