论多边形中轴问题和算法

比较了当前国内外GIS中和计算几何中关于多边形中轴的定义,讨论了它们的主要特点,指出多边形中轴应是到两个以上边距离相等点的轨迹,并据此分析了相应的各种算法和实际应用场合,提出了理论上较为严密、能够广泛满足实际应用需要的几何方法———点对序列法和地图代数多边形中轴法。     

Numerical Evaluation of the Robinson Projection

The Robinson projection is one of the most preferred projections for world reference maps in atlas cartography. The projection is constructed from Robinson's look-up table since there are no analytical formulas. This deficiency has led to a number of requests for the plotting formulas to which cartographers have responded by deriving analytical equations using different interpolation algorithms applied to Robinson's table values. The Robinson projection was examined with regard to its deformations calculated by four different algorithms, including the multiquadratic method. The numerical evaluations were then used to compare the algorithms. Solutions have been presented including some criticisms about this projection. The latitudes along which the scale is true and on which the maximum angular distortion equals zero have been determined.     

Interpolation of Point Values From Isoline Maps

A Bidirectional Hermitian Spline (BHS) method for the estimation of point values from isoline maps is presented and compared to three other methods. Hermitian splines are used and first derivatives are estimated by either Akima's method or by a clamped cubic spline, if Akima's method returns a zero first derivative. Every desired point value is interpolated twice, once by each of two orthogonally-directed splines. The two spline estimates are then averaged using the error formula for Hermitian splines. In addition, a periodic Hermitian spline is constructed around the study-area perimeter (representing a cross-sectional profile of the edge) to damp undesirable edge effects. Point values can be estimated from small-scale isoline maps drawn in spherical coordinates or from large-scale isoline maps drawn in Cartesian coordinates.     

道路平面测设计算的通用公式

基于各类道路线型曲率呈线性变化的共同特性,给出了线元上任意点坐标方位角的统一计算公式,进而提出了适用于所有道路线型平面测设计算的中桩坐标、边桩坐标的通用公式。在此基础上,讨论线路外一点对应中桩的计算以及直线与线路交点的计算,给出了相应的计算方案。     

Producing Intermediate Contours from Digitized Contours

Contour lines on existing maps are often the only source of information about the terrain relief. In an effective digital mapping environment, the generation of intermediate contours is one of many essential capabilities. These intermediate contours can be generated in the original units or in some other units. During the digitization process, errors are introduced into the cartographic data, and data manipulation processes may introduce additional errors. A new six-step method is presented here to reduce the data manipulation errors during the process of generating intermediate contours. In our method, the original digitized contours serve not only as a data source, but also as a control on the interpolation process. This process utilizes one- and two-dimensional filters to determine the differences between original and modeled contours. The interpolated contours are adjusted to the original contours thus preserving both general and local shape of the original relief representations. The most frequent application of this method likely will be in the conversion of “foot” contours to “meter” contours.     

航空影像上道路中心线的半自动提取算法研究

提出了一种新的从航空影像上提取道路中心线的半自动方法。该方法利用道路地物的几何特征和辐射特征,根据用户提供的少量道路种子点,利用自适应灰度模板对道路中心线上的每个点进行调整,最后采用最小二乘算法和牛顿迭代法对调整后的道路中心线上的每个点进行拟合,以此获得趋近于道路中心线的最佳折线。试验结果证明,该算法简单易行、效率较高．具有较好的鲁棒性和实用性。     

River centerline extraction using the multiple direction integration algorithm for mixed and pure water pixels

The river centerline is a basic hydrological characteristic. Most prior studies have used remote sensing data to extract the river centerline from the open water region in a pure water pixel region. Extracting this type of river is relatively easy. However, extracting the centerline of a micro-river, which is mainly composed of mixed water pixels, is challenging. This paper presents a novel method, called the Multiple Direction Integration Algorithm (MDIA), to extract the river centerline using an image-enhancing method combined with river morphology. MDIA can be applied to regions mainly composed of pure water pixels, as well as to regions consisting of mixed water pixels in the index image. The method first calculates the normalized difference vegetation index (NDVI) and enhances the river linear structure using a Hessian matrix. Second, a small window is constructed as a circular structural element. In the window region, the local threshold is automatically obtained using water-oriented clustering segmentation and prior river knowledge to judge the pixel type. After completing the river centerline extraction in the current window, the next detecting window is generated to continue judgment. The structural element automatically executes river centerline judgment until the entire river centerline is extracted. The Landsat 8 images of six regions with different geomorphologies were chosen to analyze the method’s performance. The test sites include high mountain region, low mountain region, plains region with farmland and a residential region. The experimental results show that the optimal threshold of the processing results ranged from 0.2 to 0.3. In this range, the user’s accuracy is 0.813 to 0.997, and the producer’s accuracy is 0.981 to 1. The MDIA effectively and correctly extracts the river network in mixed-pixel regions. The presented method provides an effective algorithm for river centerline extraction that can be used to expand and update river datasets and provide reliable river centerline data for relevant hydrology studies.     

基于公路GIS的中线里程值实时显示算法

在公路GIS中,隧道、桥梁、涵洞、排水槽等的具体位置都是通过公路中线里程桩(桩号)来确定的,为将这些目标标定在图上或在图上实时显示出公路里程值,必须将桩号换算成地图坐标或将公路在地图上的坐标换算成桩号。本文结合某一公路地理信息系统的开发实例,探讨了公路中线里程值实时显示功能实现的原理和算法,并利用编程语言VB6.0与MapX控件实现了这一功能。     

A Snake-based Approach for TIGER Road Data Conflation

The TIGER (Topologically Integrated Geographic Encoding and Referencing) system has served the U.S. Census Bureau and other agencies' geographic needs successfully for two decades. Poor positional accuracy has however made it extremely difficult to integrate TIGER with advanced technologies and data sources such as GPS, high resolution imagery, and state/local GIS data. In this paper, a potential solution for conflation of TIGER road centerline data with other geospatial data is presented. The first two steps of the approach (feature matching and map alignment) remain the same as in traditional conflation. Following these steps, a third is added in which active contour models (snakes) are used to automatically move the vertices of TIGER roads to high-accuracy roads, rather than transferring attributes between the two datasets. This approach has benefits over traditional conflation methodology. It overcomes the problem of splitting vector road line segments, and it can be extended for vector imagery conflation as well. Thus, a variety of data sources (GIS, GPS, and Remote Sensing) could be used to improve TIGER data. Preliminary test results indicate that the three-step approach proposed in this paper performs very well. The positional accuracy of TIGER road centerline can be improved from an original 100 plus meters' RMS error to only 3 meters. Such an improvement can make TIGER data more useful for much broader application.     

GB-SAR导轨倾角引起的影像坐标投影变换误差分析

依据GB-SAR传感器运行导轨与成像投影面的空间关系,分别推导了导轨中心线俯仰角和横轴侧倾角所引起的成像投影误差的计算公式。计算结果表明,导轨安装定位时产生的俯仰角通常可以忽略不计,而成像投影误差对导轨横轴的侧倾角更为敏感。在GB-SAR连续变形监测应用中,导轨的横向姿态需做严格控制,确保其水平度。     

基于角度纹理特征及剖面匹配的高分辨率遥感影像带状道路半自动提取

提出了一种基于角度纹理特征及剖面匹配相结合的高分辨率遥感影像带状道路半自动提取方法.该方法由用户输入道路起点、初始方向及宽度,使用角度纹理特征模型预测初始的道路中线点,以抛物线方程参数构建道路中线轨迹参数模型.使用计算曲率变化的方法验证道路轨迹点,对验证失败的中线点位使用剖面匹配算法进行重新预测并确定,最终提取出该道路中线轨迹.本文使用Visual C 构建了原型系统,对QuickBird及IKONOS影像中具有一定宽度的带状道路进行了提取试验,并与经典的基于剖面匹配的半自动道路提取算法和基于Snakes的半自动道路提取算法进行了对比试验.经试验验证,本算法取得了较为理想的结果.     

Cartographic Notes

On a previously-digitized map, a series of 685 points were screen-digitized so as to represent major spatial features of each polygon composing 17 forest types having inherently uncertain boundaries; three forest types having precise boundaries were treated as such. From these points and three exact types, surfaces were generated which provided weights of the certainty of having each of the 20 forest types at a location. These surfaces were “reconstituted” into a thematic map by assigning each location to the type having the highest weight. When compared to the precisely digitized and rasterized map, areal and locational inaccuracy were 5% and 18%, respectively, for the reconstituted thematic map. For certain situations—such as the preparation of long-term forest management plans—these results show promise for adequately representing maps of natural features while reducing digitizing efforts.     

Monitoring of River Center Line and Width—A Study on River Brahmaputra

Monitoring of river width and centerline is one of the most important activities in river engineering. Changes in the width and center line can be attributed to several reasons and monitoring these changes can be conveniently achieved with the aid of remote sensing images. In this study, digital image processing techniques have been implemented using the image processing tool-box available in MATLAB for studying temporal variations of width and centerline of the river Brahmaputra in its 300 Km reach in the state of Assam, India. The current study uses relatively high resolution imageries acquired from the LANDSAT series of satellites. Apart from the LANDSAT imageries, the low resolution imageries acquired by MODIS program is also used in order to see the variation in the obtained results. The evaluation of the results shows that the digital image processing technique is very handy and can be applied to obtain the centerline and width of a river. The evaluation also shows that the low resolution image can also be used for obtaining centerline of a river. However, it may give erroneous result when width of the river is narrow or very large.     

支持突发事件应急反应的建筑物内部交通网络分析

应用基于节点关系的3维拓扑数据模型,建立了建筑物内部通道的几何网络,较详细地讨论了走廊多边形的中轴线求取算法。然后基于图论算法对建筑物内部通道情况进行分析,并给出分析结果的3维表示。该方法对基于GIS的多层建筑物内的突发事件应急处理系统具有参考作用。     

轨道交通中线测设统一数学模型的建立

根据对常用的两种中线测设数学模型的分析，从线路中线曲率半径的特点出发，提出了中线整体积分数学模型，并导出其计算公式。为了实现整体积分模型的计算，对龙贝格积分算法进行了改进，并用于武汉市轨道交通一号线一期工程的中线测设。比较和分析表明，从实用性和精度等方面来说，整体积分模型是目前轨道交通最优的中线测设模型。     

快速提取城市道路中心线

城市道路在空间分布上具有一定的规则。我国的城市道路布局主要有方格式、扇形式等。本文针对这种布局规则的道路网,提出一种快速提取道路中心线的方法。通过对图像进行扫描,将属于一条道路的所有像素点归并到一个容器中,提取中心点并输出成道路线。同时,介绍了几种典型道路的处理方法。实验研究表明该方法可以快速、精准地提取道路中心线,具有实际应用价值。     

Rapid K-Neighbor Identification Algorithm for the Sphere

Spatial searching, such as the identification of k-nearest neighbors to a point, is one of the most time-intensive tasks in vector-based geographic information systems transformational or analytical operations, and as such continues to impede many studies. While a number of computationally efficient k-neighbor searching algorithms have been developed for d-dimensional monotonic coordinate axes, these methods are inappropriate for spherical coordinates necessary in many global studies. This article briefly examines the assumptions and resulting limitations of k-neighbor searching algorithms with spherical coordinates. One of the simplest, yet most efficient k-neighbor searching algorithms is applicable to spherical applications, if constrained. Comparisons between the processing efficiency of the brute-force searching method commonly in use, a constrained heuristic k-neighbor searching algorithm, and a modified k-neighbor algorithm indicate processing times may be decreased by as much as 99% using such rapid searching methods in global geographic applications.     

Evaluation of the quality of an online geocoding resource in the context of a large Brazilian city

Geocoding urban addresses usually requires the use of an underlying address database. Under the influence of the format defined for TIGER files decades ago, most address databases and street geocoding algorithms are organized around street centerlines, associating numbering ranges to thoroughfare segments between two street crossings. While this method has been successfully employed in the USA for a long time, its transposition to other countries may lead to increased errors. This article presents an evaluation of the centerline‐geocoding resources provided by Google Maps, as compared to the point‐geocoding method used in the city of Belo Horizonte, Brazil, which we took as a baseline. We generated a textual address for each point object found in the city's point‐based address database, and submitted it to the Google Maps geocoding API. We then compared the resulting coordinates with the ones recorded in Belo Horizonte's GIS. We demonstrate that the centerline segment interpolation method, employed by the online resources following the American practice, has problems that can considerably influence the quality of the geocoding outcome. Completeness and accuracy have been found to be irregular, especially within lower income areas. Such errors in online services can have a significant impact on geocoding efforts related to social applications, such as public health and education, since the online service can be faulty and error‐prone in the most socially demanding areas of the city. In the conclusion, we point out that a volunteered geographic information (VGI) approach can help with the enrichment and enhancement of current geocoding resources, and can possibly lead to their transformation into more reliable point‐based geocoding services.     

基于Delaunay三角网的河流中线提取方法

鉴于水系自动综合中河系数据模型建立的复杂性,利用ArcObject提供的组件在双线河和狭长湖泊间构建约束的Delaunay三角网,继而提取其骨架线,从而得到双线河和狭长湖泊的中轴线,之后进行拓扑关系的保持,有效地简化了水系数据模型的建立,为后续的空间分析打下基础。     

地理国情水系要素的自动提取

在地表覆盖水系图斑采集的基础上,利用Rosenfeld细化算法实现地理国情水系要素中心线的自动提取。首先兼顾提取质量确定图像由矢量转换为栅格的最佳像素值,然后根据内存访问效率和图像块大小的关系选择图像分块处理技术。此外,采用图像形态学的膨胀与腐蚀算法、线段长度条件约束和曲线节点抽稀等技术确保中心线提取质量。试验结果表明,本文提出的方法准确、高效,在生产实践中具有一定的应用价值。