Real-time raster projection for web maps

The virtual globe is the default visualization for Digital Earth applications, but it can only show one half of the Earth. This article introduces user-adjustable, on-the-fly projection of georeferenced raster images for web mapping and web GIS applications. This technique allows users to center a map on arbitrary locations, while still seeing the entire Earth surface. Modern web mapping libraries can apply map projection transformations to vector data in the browser, but they do not currently support the projection of raster images at interactive frame rates. We use the cross-platform WebGL (Web Graphics Library) graphics pipeline for hardware-accelerated projection of raster data in web browsers. Two algorithmic techniques – inverse per-fragment projection, and combined forward per-triangle and inverse per-fragment projection – for georeferenced raster imagery are documented. The resulting raster maps combine the ease of use and flexibility of interactive virtual globes with the ability to show the entire Earth. The adjustable projection of raster imagery allows users to observe global phenomena that are difficult to visualize on virtual globes or traditional maps with static projections.     

矢量Web网络地图应用研究

矢量数据的分块组织和渐进传输是解决海量矢量数据Web应用的重要手段。针对当前大数据背景下,单一的渐进传输方法对减少数据量的效果有限,且不能满足根据可视区域进行数据传输,提出了分块渐进传输的方法,结合Google Maps瓦片切分方案对数据进行分级分块处理,得到多分辨率矢量瓦片数据,结合矢量要素的属性意义这一因子,对其进行重要性排序,分批次选取传输,然后考虑显示窗口大小的因素,在数据调用中最大限度地减少瓦片数据的拼接,提高可视化渲染效率。最后通过实验实现服务器端矢量数据的分级分块组织以及选取操作,建立数据的多分辨率表达模型,在客户端进行调度显示,形成一套矢量数据分块渐进传输体系,为矢量地图数据的Web应用提供了可借鉴方法。     

电子地图海量专题要素麻点图技术研究

针对JavaScript成为目前Web电子地图开发的主流技术,而浏览器能承载的数据量和JavaScript的渲染能力有限的问题,该文通过对基于栅格图片的模式和基于插件的矢量数据模式的对比分析后,基于矢量瓦片技术、空间搜索技术和实时渲染技术等关键技术,提出了对海量专题要素进行服务端与客户端协同处理、实时分级渲染的麻点图技术方案,实现了海量专题要素的实时渲染和即时交互,并应用在"天地图·陕西"电子地图系统中。     

面向目标的栅格矢量一体化三维数据模型

首先对现有的三维空间数据模型进行了讨论 ,分析了栅格、矢量和混合数据模型的特点 ,提出了一种面向目标的栅格矢量一体化数据模型。该模型将栅格数据以矢量方式进行组织 ,从而同时具有矢量和栅格数据模型的优点 ,也克服了目前普遍应用的混合模型所存在的缺点。还提出了一种三维空间的三级栅格划分和行次序编码方法。该方法存储空间小 ,便于快速索引和计算。最后 ,给出了具体的数据结构     

基于Html5的Web Map矢量渲染技术研究

当下主流平台(即桌面PC,Android,IOS等)上Web浏览器都支持Html5标准。Html5的到来让Web应用的性能和易用性明显提升,其中Canvas元素是Html5标准中新增的技术之一,被JavaScript用来进行图形图像的绘制和矢量渲染。针对传统切片式Web Map存在的不足,文中以Web地图矢量渲染为研究切入点,分析一种基于JSON的地理信息数据传输格式,并使用Html5Canvas构建矢量Web Map,即在浏览器中地理数据矢量渲染的设计和实现,兼具自定义渲染风格而无需重新请求加载图层,减少瓦片请求所需的带宽,改善Web Map实时显示的性能,探索进一步直接实现Web Map空间分析能力的可行性。     

Advancements in web‐mapping tools for land use and marine spatial planning

Land use and marine spatial planning processes are increasingly supported by systematic assessment techniques, particularly by multi‐criteria spatial analysis methods. This has been facilitated by the growing release and uptake of web‐mapping tools, which contribute to transparent, consistent, and informed planning processes and decisions. This article reviews the usability, functionality, and applicability of contemporary planning web‐mapping tools to identify the state‐of‐the‐art and future prospects. The review reveals that interfaces are increasingly available and intuitively applicable by non‐specialized users. Basic map navigation and data querying functionality is being expanded to incorporate advanced map‐making and online data geoprocessing capabilities that enable deriving new data and insights. However, the majority of published planning web tools are one‐off solutions, and a disconnect between research and practice is rendering many of these inaccessible or obsolete. Despite the significant progress made in advancing their provision in the last decade, there is a need for developing transferable interfaces that are maintained beyond project end dates, for them to effectively and consistently support planning processes.     

栅格数据矢量化及其存在问题的解决

矢量结构和栅格结构是GIS的两种主要数据结构形式，而栅格数据的矢量化在GIS中具有十分重要的意义。本文在总结前人算法的基础上，以拓扑关系的原理为指导，提出了改进的栅格结构数据矢量化方法，即在提取结点和坐标点过程中同时提取水平和垂直的所有线段信息，以便于快速、有效地实现栅格数据的矢量化。此外，还采用动态打断和粗网格法等方法，解决了在栅格数据矢量化过程中经常出现的诸如多边形自交、岛等问题。     

基于拓扑关系原理的栅格转换矢量方法的研究

从与传统方法不同的角度着手,以拓扑关系为指导,研究了一种新的由栅格数据转换为矢量数据的方法。与传统转换方法相比,该方法不需对栅格数据进行预处理,它在转换过程中即形成拓扑关系,只需对图像数据逐行处理一次,故适合于大图像的处理。该方法转换效率高、速度快,并在试验中取得了很好的效果。     

The Potential of Maps APIs for Internet GIS Applications

Since the launching of Maps Application Programming Interfaces (APIs) in 2005, many web developers, including geographers and non‐geographers, applauded the freely adaptable tools and used them to spawn numerous Internet applications. The success of the Maps APIs is largely attributable to its no‐cost policy, the availability of global data coverage, dynamic navigation, query capability, and ease of implementation. Despite its versatility in dynamic exploration of geographic data online, the existing Maps APIs lack Geographic Information System (GIS) functionalities compared to other Internet Mapping Services. The goal of this research was to review the potential of the Maps APIs for Internet GIS applications. This research employed the Google Maps API and developed a web prototype that disseminates spatial information of urban sprawl in Mundy Township, Michigan. The results revealed that both vector and raster data could be effectively represented by using the Maps API. Moreover, the Geographic Markup Language (GML) approach illustrated great potential for developing Internet GIS solutions around open specifications. This research suggested several potential solutions to expand the spectrum of GIS operations of the Maps APIs by incorporating the XML‐related technology and extending the JavaScript library.     

基于多协议的地理信息服务集成

设计了多协议地理信息服务集成框架,探讨解决了其中的关键问题,实现了从不同地理信息服务获取的影像数据、矢量数据和DEM数据的无缝集成。     

地图切片技术分析与简单实现

地图切片(MapTile)技术是目前大多数电子地图网站、3维地图网站使用的预先生成栅格地图,并由客户端接口呈现出无缝拼接地图的浏览技术。地图以链接图片的方式快速定位,访问速度要快于传统的WebGIS,同时,对地图服务器的负载也相应小一些。本文介绍了地图切片技术的相关步骤并对主流电子地图网站做了分析。笔者利用Flash作为地图客户端开发工具,实现了地图切片的实时加载和不同比例尺的漫游。     

GIS中面状要素矢量栅格化的面积误差分析

在探讨矢量栅格化的几种形式和产生误差原因的基础上,系统分析在面状要素矢量栅格化的误差分析方法研究方面所取得的进展,指出当前分析方法存在的主要问题,并提出利用结构性栅格数据进行面状要素矢量栅格化的误差分析方法,然后以土地利用数据的栅格化为例进行实证研究。研究表明,常规分析方法很大程度上低估了栅格化的误差,因为没有充分考虑栅格化误差存在空间上的"此消彼长"现象。建议采用结构性栅格数据来改善栅格化误差分析,对误差作基于格网的量化计算,并标记在单元格上。它能有效地区分"此消"与"彼长"导致的误差,使面状要素栅格化的误差分析更加全面、客观、准确,且容易进行误差的量化分析与表示。     

遥感分类栅格图的快速矢量化方法

遥感数据成为GIS愈来愈重要的一种数据源.栅格数据与矢量数据之间的快速转换是RS与GIS集成中的关键技术之一.本文通过分析遥感分类图栅格像元之间的关系,快速自动地提取矢量数据点及其连接信息,进而利用连接信息快速生成弧段,由弧段自动组建多边形并建立完整的拓扑关系.实验表明,该方法是一种由遥感分类图自动转换成GIS通用数据的高效方案.     

图形、图像融合利用的集成学习智能化简方法及其在岛屿岸线化简中的应用

为充分利用已有化简成果及其蕴含的化简知识,本文集成几种机器学习算法提出图形、图像融合利用的智能化简方法,实现顶点取舍决策的学习和优化。首先,分别利用全连接神经网络和卷积神经网络设计、构建基于图形的顶点取舍模型和基于图像的顶点取舍模型,通过样本训练各模型拟合从图形特征到顶点取舍和从栅格图像到顶点取舍的映射;然后,基于线性加权、朴素贝叶斯、支持向量机、人工神经网络构建多种融合决策模型,实现基于图形和基于图像的顶点取舍的融合利用;最后,通过试验用例对所有模型进行测试。试验结果表明：基于图形和基于图像的顶点取舍模型在一定程度上学习、掌握了化简算子,融合利用后还能进一步提高化简准确性、实现优势互补。     

一体化空间数据结构及其索引机制研究

本文提出了一种新的栅矢一体化空间数据结构,该结构采用三级划分策略及几何目标元子充填表达技术,使空间数据栅格化的同时,也能满足精度要求。同时引入弧段栅格比特阵和面要素自适应空间索引结构,有效地提高了空间检索效率。试验证明,上述理论及方法是可行的。     

2.5维电子地图渲染成图接边方法探讨

2.5维电子地图与二维、三维矢量地图有着明显区别,其分批渲染成果是栅格数据,最后成果也是图像的形式,所以在地图接边的方式上比矢量图接边的方法要复杂得多。本文探讨了一种方法,使用虚拟相机确定2.5维电子地图俯瞰视角,制作批量渲染成图的接边参考框架,最后分批渲染景观模型与框架进行图像叠合。这种方法在项目实践中初见成效,能最大限度地缩小接边误差,不足之处是人工干预部分较多,必然导致误差累积,有待改进。     

Geographical Linked Data: The Administrative Geography of Great Britain on the Semantic Web

Ordnance Survey, the national mapping agency of Great Britain, is investigating how semantic web technologies assist its role as a geographical information provider. A major part of this work involves the development of prototype products and datasets in RDF. This article discusses the production of an example dataset for the administrative geography of Great Britain, demonstrating the advantages of explicitly encoding topological relations between geographic entities over traditional spatial queries. We also outline how these data can be linked to other datasets on the web of linked data and some of the challenges that this raises.     

An open source,server-side framework for analytical web mapping and its application to health

In this paper, we detail the design and the implementation of an open source, server-side web mapping framework for the analysis of health data. The framework forms part of a larger project, the goal of which is to provide an analytical web geographical information system (GIS) that enables health experts to analyse spatial aspects of health data. The aim of the framework is to provide a method for the dynamic and flexible spatial visualisation of health data to facilitate data exploration and analysis. Consequently, a dynamic thematic web mapping technique, an extension to the Open Geospatial Consortium (OGC) web map service standard, was developed. The technique combines a data query, processing technique and styling methodology on the fly to generate a thematic map. The resulting thematic map represents a virtual map layer that enables a user to rapidly visually summarise properties of a data-set. A test web interface was developed to assess the efficacy of the web mapping technique. As the dynamic web mapping method builds on existing OGC web mapping standards, it can be readily integrated with the existing lightweight slippy map web clients and virtual globes.     

一种顾及符号完整性的矢量瓦片地图改进方案

在矢量瓦片地图中,跨网格的要素被分割成多个部分,常常造成点、线、面要素中非均匀符号在网格边界处的不连续,这样不仅影响视觉效果,还容易引发空间认知错误.在保持矢量瓦片数据和样式独立的基础上,提出使用预处理和实时绘制相结合的方法解决这类问题.通过分析不同要素符号在网格边界不连续的类型和原因,提取了不同类型的绘图辅助信息;将...     

A Hybrid System of Expanding 2D GIS into 3D Space

A hybrid system that integrates two-dimensional (2D) GIS and three-dimensional (3D) visualization has been developed to provide unique solutions to application domains where traditional 2D GIS and 3D visualization cannot alone provide a solution. In this paper, we focus on three key issues in realizing such an integrated system, including large-scale terrain rendering, 2D and 3D combination display (for example, rendering 2D GIS layers in 3D space), expanding traditional 2D GIS analysis functions into a 3D environment, and visualizing 3D geographical data. A generic framework is developed to integrate 3D visualization with various types of 2D GIS, such as commercial GIS software, open source GIS software and spatial databases. A prototype 2D and 3D hybrid system that seamlessly integrates 2D GIS (developed with ArcEngine) and 3D rendering engine (developed with DirectX) is then developed based on the framework. In this hybrid system, 2D and 3D data are viewed within the same scene. Multiple 2D GIS layers are overlaid on the base terrain using a Level of Detail (LOD) model. Advanced query functions, data accessing, data management and spatial analysis, which are executed in the traditional 2D GIS, are provided to users in a 3D environment by continuously transforming information between the 2D GIS subsystem and the 3D subsystem. The 3D data are organized and displayed by Keyhole Markup Language (KML) and textured 3D models in the COLLAborative Design Activity (COLLADA) format. The prototype demonstrates that this hybrid system has effectively addressed the three key issues identified above and that it can seamlessly integrate 2D GIS and 3D visualization. The hybrid system has great potential to be employed in many application domains, such as urban planning, landscape design and environmental decision making, among others, to enhance the 3D design capability and facilitate public participation in the planning, design and decision-making process.