共查询到18条相似文献,搜索用时 93 毫秒
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海图数据库是海图生产自动化和GIS等应用系统的基础,其性能直接影响到这些应用系统的开发和使用的可能性及便利程度。遗憾的是目前一般是把海图数据库系统的功能局限在数据的采集、存贮、提取以及图形的原样回放上,而没有顾及不同用户对数据量和图形化简的不同要求,这无疑降低了数据库系统的潜在价值。 本文首先论述了海图数据库系统需要拥有制图综合功能的几种情况,然后结合海图制图特点,简要分析海图数据库系统中制图综合功能的实现方式及与制图综合功能模块有关的一些问题。 相似文献
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在地理信息领域,"图示表达"用于表示要素从数据变换为图形显示这一过程,其中,建立数据与图形的映射规则是核心问题。由于现行电子海图标准S-52过于封闭难以拓展的问题,电子海图的图示表达相对复杂,制约了标准化海图显示技术的发展。为此,以S-52为重构对象,引入XML标准(可扩展标记语言),提出了"电子海图全XML图示表达模型",重点分析并构建了基于XSLT(可扩展样式表转换语言)的电子海图图示表达规则,实现了电子海图数据与图形的解耦合,为电子海图的开放共享和多样化表达奠定了基础。 相似文献
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利用TrueType字体文件构造海图符号库 总被引:1,自引:0,他引:1
近几年,数字海图已由研制阶段逐渐过渡到规模化生产,其标准化工作也接近完善。本文介绍了关于数字海图显示的研究中,通过对TrueType字体文件和WindowsGDI函数的研究,设计了用TrueType字符和WindowsGDI图形函数结合构造海图符号库的算法,并通过VisualC++程序实现,在数字海图的显示中也得到了很好的应用。 相似文献
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本文介绍了将海图图形信息和拓扑关系信息用链索引结构存放在同一个海图文件中的一种较复杂的数据结构,并提出了采用速查标记BITMAP、坐标极值、数据实体细检索的三级要索检索方法,大大提高了地理信息的检索与捕捉速度。较详细地给出了各类要素的速查标记BITMAP的生成算法,最后介绍了在一个系统中进行地理信息快速检索与捕捉的具体实现过程。 相似文献
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Wenhao Yu 《Marine Geodesy》2018,41(1):68-85
Sounding acts as the main feature in a digital nautical chart as it describes the concerned marine topography for the safety of navigation. Unlike the geometry-oriented selection of point feature, the generalization of soundings for chart compiling is expected to be context-oriented, which means bathymetry complexity variations across the study region should be preserved in the sounding selection process. However, such variations are not explicitly accessible to automated systems. This paper proposes an approach that effectively analyzes and measures bathymetry complexity from sounding data, with a focus on topography variations among different regions. The presented approach first divides the exploring region into several subregions, by adopting techniques of computational geometry and graph theory. Then, the approach quantitatively measures the bathymetry complexity of the subregions from grid-based digital terrain model. Finally, a composite bathymetry complexity index integrating aspects of steepness and depth variation is developed to guide the operation of sounding selection in different subregions. Generally, when seafloor is rugged with steep slopes, the number of soundings is high. While in flatter areas, a smaller amount of soundings is retained. The potential of our approach is demonstrated by an application to a real data set. 相似文献
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针对建筑物多边形化简当前存在的问题,将参数优化的方法引入化简的全过程,在渐进式图形化简的基础上,通过把建筑物多边形的几何特征、结构特征和化简所遵循的一系列约束规则参数化、变量化表示,建立了建筑物多边形化简的数学模型,通过对模型的求解,来达到化简建筑物多边形的目的。 成果已经应用于数字地图的生产,实践证明该算法的化简效果好,普适性较高,符合应用需求。 相似文献
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多核模糊聚类算法的研究 总被引:3,自引:0,他引:3
针对多类样本数据,提出1种多核模糊聚类算法。通过选取子核函数及其参数构造多核函数,使得输入空间的样本经多核函数映射后,增大不同类别样本间的差别,提高核函数的学习能力和泛化能力。聚类实验表明,多核函数模糊聚类对于多类样本数据具有比单核更好的聚类效果。 相似文献
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Generalization is a comprehensive process. It is not simply a question of an algorithm, such as simplification, selection, displacement, and so on. Only after geometric shapes and topological properties have been understood fully, can a sound and automated generalization process be possible. This article proposes a new theoretical model for sounding generalization in digital nautical charts. First, with the aid of Delaunay triangulation, a tree structure is introduced for a hierarchical representation of the marine topography. Then, an analytical algorithm for the recognition and the measurement of the marine topography is developed through the use of the tree structure. Finally, all of the techniques mentioned above are integrated into a model for sounding generalization, of which results are illustrated with the aid of several examples. 相似文献
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Generalization is a comprehensive process. It is not simply a question of an algorithm, such as simplification, selection, displacement, and so on. Only after geometric shapes and topological properties have been understood fully, can a sound and automated generalization process be possible. This article proposes a new theoretical model for sounding generalization in digital nautical charts. First, with the aid of Delaunay triangulation, a tree structure is introduced for a hierarchical representation of the marine topography. Then, an analytical algorithm for the recognition and the measurement of the marine topography is developed through the use of the tree structure. Finally, all of the techniques mentioned above are integrated into a model for sounding generalization, of which results are illustrated with the aid of several examples. 相似文献
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为满足科学管理海岛海岸带的需求,发掘合成孔径雷达(SAR)在海岛海岸带地物信息提取中的应用潜力,文章概述SAR和卷积神经网络的原理,分析卷积神经网络应用于SAR遥感海岛海岸带地物信息提取的可行性和优势。研究结果表明:通过卷积神经网络提取SAR数据中的海岛海岸带地物信息,无须预先提取图像特征,卷积神经网络能够自动提取图像中更本质和更抽象的特征,更好地应对地物目标的非线性混合;这种提取方法的精度更高,鲁棒性和泛化能力更强,可应用于海岛海岸带的精细化监测,为海岛海岸带的科学管理提供支撑。 相似文献