复杂多边形中轴构建方法!

多边形中轴是指与多边形不同边(或边的延长线)上的两个或两个以上点等距离的点轨迹。多边形中轴的图形结构表明,在多边形凸顶点处存在中轴线,而在凹顶点处不存在中轴线(中轴线在多边形外)。采用左右点法实现对多边形顶点凹凸性的判断,进而定义和标注多边形不同边界线段。借助ArcGIS软件,提出了构建任意复杂多边形中轴的两种逼近方法:一种是基于Voronoi图的矢量方法;另一种是基于欧氏距离区域分配的栅格方法。实验表明这两种方法都是有效的、可行的。     

一种构建复杂平面图形中轴的方法

提出了中轴矢量逼近构建任意复杂平面中轴的方法。以一种简单、有效、稳定的构建任意平面图形中轴的方法为例,采用不同密度的点逼近原始图形边界,构建这些点集的约束Delaunay三角网,然后构建Delaunay三角网的三角形外接圆圆心,圆心的轨迹即是原始图形的中轴。数值实验表明,约束Delaunay三角网方法可以实现对各种复杂平面图形中轴的良好逼近,并且随着目标图形边界上的点密度增加,得到的中轴越来越逼近精确中轴。     

基于CNN-DW的遥感图像分类检索方法

针对传统图像检索方法存在的检索范围过大、检索效率低下的问题,提出了一种基于卷积神经网络和距离权重的图像检索方法(CNN-DW),该方法可以从海量遥感图像中检索出与查询图像具有相似或相同特征的检索图像,图像检索试验表明:CNN-DW检索法较传统卷积神经网络(Convolutional Neural Networks,CNN)检索法的分类检索效果有显著提升,仅需要更少数量的训练集就能达到良好的检索效果,可在遥感图像分类检索工作中予以合理运用.     

曲边多边形中轴提取的新方法

针对现有多边形中轴提取方法在处理复杂图形和特殊图形上有较大困难的不足以及中轴连通性和位置准确性难以保证等问题,提出了一种曲边多边形中轴提取的新方法。首先在简单多边形的基础上进行拓展,提出曲边多边形的概念,并相应地定义了曲边多边形的中轴,然后在栅格距离变换的基础上引申出最近边缘点集距离均值变换,最后结合曲边多边形中轴点的特征和距离变换的原理制定出高效中轴点判定规则,利用种子点生长判别法提取曲边多边形的中轴,并给出具体实现步骤和流程。通过多组不同类型多边形及道路网与河网的实例验证,新方法不仅能适用于各类多边形,且能较好地抑制图形边界噪声的干扰,提取出具有良好的光滑性、准确性和连通性的多边形中轴,弥补了传统方法的不足。     

点云数据在兰州地铁中的应用

针对提取隧道点云中轴线3种不同算法,选择更加适合海量点云中轴线提取的算法。首先对隧道点云进行坐标转换,按里程对隧道点云进行连续正交断面的提取,将得到的断面通过椭圆模型进行粗差剔除;其次采用RGB颜色变化值表示断面的收敛扩张情况,通过柱状图、折线图表示断面形变特征;最后对隧道曲线段点云数据进行中轴线的提取,并进行平曲线要素的自动提取,为隧道平曲线主点位置识别、平曲线要素提取提供一种新途径。     

基于结点逼近提取的平面点集Voronoi图构建算法

提出一种基于结点空间逼近、精确提取以及面向拓扑关系生成的2维平面点集的构建方法。主要给出了搜索矩形域及其剖分概念、Voronoi图的基本性质、矩形域与Voronoi图结点关系的定理及其证明、基于链队的矩形域剖分和结点逼近机制及结点提取策略、基于条带有序表的最近邻近发生元快速检索算法、矢量Voronoi图的拓扑关系建立算法等。经过算法分析和程序试验验证本文算法的时间复杂度为0（n log2 n）,本方法可以扩展到平面任意发生元Voronoi图的构建,具有简洁、高精度、鲁棒性、高效、适合于海量数据等特点,并且具有较好的实用价值和应用前景。     

矢量GIS中随机折线定位不确定性的可视化模型

折线是ＧＩＳ中表达线形空间实体的基本制图要素。本文针对由随机折线点构成的折线要素建立了一种可视化误差模型。首先引入了随机折线要素误差带的基本概念,并导了误差带的边界线数学方程;然后针对开折线和闭折线两种情况绘出了误差带的可视化图形,并分析了形状特征,从而将单一随机折线元的误差带理论进一步扩展到一整条随机折线的一般情况。     

折线光滑处理的三点算法研究

在地理信息系统（GIS）中,为了使地图线状要素数据的可视化有较高的质量,就需要对线状要素进行光滑处理。如何使得折线光滑后,让原始点更多地保留下来,是衡量该类地图数据精度的重要依据。本文提出了一种折线光滑处理的三点算法,该方法拟合精度高且算法简单,具有较强的实用性,可用于自动化制图、GIS等地图线状要素的绘制中。     

基于约束性Delauney三角网确定多边形中轴线的研究

建立在多边形约束性Dolaunoy三角网的基础上，针对确定多边形中轴线的特点，提出了表层三度单元、内核三度单元、单入口路径表层三度单元、双入口路径表层三度单元、三入口路径表层三度单元等概念体系，最后提出了确定多边形中轴线的算法模型，并进行了实验性验证。理论与实验表明该模型逻辑严密，结论正确，研究成果对多边形的形态分析、地图上面状要素的注记定位等问题具有基础支持作用。     

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。     

阿克苏河-塔里木河水系水质污染遥感监测与评价

 采用Landsat TM数据分析了阿克苏河—塔里木河断面水质污染状况,通过波段的DN值和常规监测数据建立能反映水质状况的 污染物监测模型。结果发现,将2000年常规监测数据代入模型后,与遥感数据的结果基本吻合| 重建阿克苏河—塔里木河的连续水体 污染变化曲线,得出污染物浓度随着远离上游而增加。     

Monitoring drought dynamics in the Aravalli region (India) using different indices based on ground and remote sensing data

The hard-rock hilly Aravalli terrain of Rajasthan province of India suffers with frequent drought due to poor and delayed monsoon, abnormally high summer-temperature and insufficient water resources. In the present study, detailed analysis of meteorological and hydrological data of the Aravalli region has been carried out for the years 1984–2003. Standardised Precipitation Index (SPI) has been used to quantify the precipitation deficit. Standardised Water-Level Index (SWI) has been developed to assess ground-water recharge-deficit. Vegetative drought indices like Vegetation Condition Index (VCI) and Temperature Condition Index (TCI) and Vegetation Health Index (VHI) have been computed using NDVI values obtained from Global Vegetation Index (GVI) and thermal channel data of NOAA AVHRR satellite. Detailed analyses of spatial and temporal drought dynamics during monsoon and non-monsoon seasons have been carried out through drought index maps generated in Geographic Information Systems (GIS) environment. Analysis and interpretation of these maps reveal that negative SPI anomalies not always correspond to drought. In the Aravalli region, aquifer-stress shifts its position time to time, and in certain pockets it is more frequent. In comparison to hydrological stress, vegetative stress in the Aravalli region is found to be slower to begin but quicker to withdraw.     

使用FME与VBA提取机场方格网高程数据

因受机场工程设计软件的测量数据容量限制,基于LiDAR采集、点云分类后得到的地面点云数据LAS不能完整应用于目前设计软件进行设计计算。本文通过对拟选技术方案的筛选,提出了利用FME Workbench数据处理功能,结合VBA编程获取外部方格网平面数据的方法。该方法在FME Workbench中实现了地面点云数据构建TIN、采用逐点内插方法从TIN中提取方格网高程数据、等高线生成及相应图形处理与成果输出。最终通过实际算例证明了该方法的有效性。     

Landslide risk analysis between Giri and Tons Rivers in Himachal Himalaya (India)

The area around Sataun in the Sirmur district of Himachal Pradesh, India (falling between the rivers Giri and Tons; both tributaries of the Yamuna River) was studied for landslide vulnerability on behalf of the inhabitants. The study was made using extensive remote sensing data (satellite and airborne). It is well supported by field evidence, demographic and infrastructural details and aided by Geographic Information System (GIS) based techniques. Field observations testify that slope, aspect, geology, tectonic planes, drainage, and land use all influence landslides in the region. These parameters were taken into consideration using the statistical approach of landslide hazard zonation. Using the census data of 1991, vulnerability of the populace to the landslide hazard was accessed. As most of the infrastructure in the region is concentrated around population centres, population data alone was used for vulnerability studies.     

Gravity Changes Before Large Earthquakes in China: 1998-2005

Although it is well known that coseismic gravity changes take place during an earthquake, previous research has not yielded convincing evidence demonstrating that significant gravity changes occur before large earthquakes. Furthermore, even if we suspect that gravity changes occur before large earthquakes, we have yet to demonstrate how to consistently observe these changes for useful earthquake forecast that would bring benefits to society. We analyzed ground gravity survey data obtained in 1998, 2000, 200...     

GNSS系统及其技术的发展研究

阐述了国际上卫星导航系统的总体发展,对美、俄、欧、中的四大全球系统,以及相关的区域系统和增强系统进行了简单的介绍,研究分析了GNSS系统及其技术的发展趋势,同时分析了我国Compass全球系统面临的机遇和挑战,并提出了我国未来工作的建议.     

自动车辆定位导航系统中传感器的误差分析

对国界定位导航系统中几种常见的辅助传感器所产生的误差进行了分析，导出了不同传感器的误差模型。这些误差模型是估计车辆位置的扩展卡尔曼滤波器的基础，同时也为选择适当的传感器提供了理论根据。     

“4D”技术及其应用

介绍“４Ｄ”（即数字地面模型、数字正射影像、数字栅格地图和数字线划地图）系列产品的生产流程、关键技术、及其在耕地保护、防灾减灾救灾和城市规划等方面的应用方法。     

Virtual Australia: its key elements – know,think, communicate

Abstract

Virtual Australia is not a well-defined or agreed concept. This discussion paper conceptualises Virtual Australia as a ‘virtual [digital] model containing and representing all non-trivial objects and their contextual environment – from blue sky to bedrock – in real world Australia’. It describes a scenario for Virtual Australia, one or two decades from now, in which the locations and conditions of non-trivial objects and their environment are updated automatically through a combination of remote sensing and wireless communication technologies in support of a ‘Supranet’. It then examines the concept of the ‘Supranet’ – a pervasive information network based largely on wireless technology linking the physical world to a virtual model in real time – and develops and discusses three principal characteristics of the Supranet: the ability to have or collect specific information (know); the ability to process information (think); and the ability to communicate that information. If, in the near future, any or all non-trivial devices are to some extent able to know, think and communicate, the potential for object autonomy will be realised.