Analysis of the EUREF-89 GPS data from the SLR/VLBI sites

In May 1989, the IAG Subcommission for the European Reference Frame organized a GPS measurement campaign, called EUREF-89, to establish a common European Reference Frame. During a 2-week period various types of GPS receivers were deployed at about 100 different locations in Europe, which included many national geodetic first order points and most of the well-known SLR and VLBI sites. In this study, the measurements from those SLR and VLBI sites, and three additional points in The Netherlands, have been analyzed adopting a fiducial network approach. In the first place, the study provided valuable experience in the use of the GIPSY software for the analysis of GPS data from large networks equipped with a mixture of receiver types. Furthermore, this analysis represents an independent check of the SLR/VLBI network, used as the reference frame for the official EUREF solution. Daily solutions of baselines up to 2500 km in length have been obtained with a repeatability of 0.5–2.0 parts in 10⁸, while the agreement with SLR results is at about the same level. The accuracy of the estimated coordinates is at a level of about 4.0 cm in the horizontal and 6.0 cm in the vertical direction. Of particular interest are the results for some baselines in Greece, which have also been measured by mobile SLR in the framework of the WEGENER/MEDLAS project. The GPS results seem to confirm the trends in the baseline length changes emerging from those SLR studies.     

车载LiDAR数据的道路裂缝信息自动提取

针对传统道路裂缝检测工作中存在的问题,该文提出了一种利用车载LiDAR数据的道路裂缝信息自动提取方法。车载LiDAR系统能够在正常车速条件下直接获取道路及其两侧各种地物的高精度、高密度表面三维数据。为了提高数据处理效率,将三维LiDAR数据转换成二维强度特征影像数据。张量投票算法根据平滑度、邻近度及连续性约束原则,通过结构特征的张量表示和非线性投票能够从稀疏的、噪声的数据中推断显著性结构。通过实验分析,该方法不仅适用于激光点云生成的强度特征影像数据的裂缝提取,还适用于光学影像数据的裂缝提取,且提取精度在90%左右。     

Using VLBI fringe-phase information from geodetic experiments for short-period ionospheric studies

The usage of Very Long Baseline Interferometry (VLBI) fringe-phase information in geodetic VLBI is a new field of research, which can be used for the detection of short-period (i.e., several minutes) variations (scintillations) of the ionosphere. This paper presents a method for the extraction of such disturbances and discusses how dispersive influences can be separated from intra-scan delay variations. A proper functional and stochastic model for the separation of the different effects is presented and the algorithms are applied to real measurements. In an example, it is shown that a traveling ionospheric disturbance in Antarctica can be detected very precisely. A possible physical origin and the propagation properties of the disturbance are presented and the results are compared with GPS measurements. The benefit of this method for other applications is also discussed.     

面向移动设备的地理信息可视化表达

随着Mobile GIS研究的深入和Mobile Computing技术的发展,这两个研究领域间出现一种相互融合的发展趋势,由于应用范围和环境的复杂性,使得移动设备中地理信息的有效利用和表达问题显得越来越突出.总结面向移动设备地理信息可视化表达的特殊性,在此基础上对面向移动设备的地理信息表达方法和手段进行研究.     

MINQUE for block diagonal bordered systems such as those encountered in VLBI data analysis

A sparse matrix method is developed for computing variance factors for block-diagonal, bordered systems of equations using MINQUE (Minimum Norm Quadratic Unbiased Estimation). This method greatly reduces the computational effort required to apply MINQUE, thus making it practical to compute variance factors for some very large systems of equations. The computer implementation of the method is described and applied to the computation of variance factors for a combination of 1609 VLBI (Very Long Baseline Interferometry) observing sessions. The purpose of this test was to compute a variance factor for each of the data sets and, perhaps, to obtain more realistic variance estimates to replace those in common use for the analysis of VLBI data. It was found that the method is satisfactory for use with such large problems, and the test served to verify that the variances in current use in VLBI data adjustments are adequate. Received: 26 November 1996 / Accepted: 12 December 1997     

Aerial remote sensing as a useful technique to obtain data on urban population

The aerial remote sensing data can be reliable source to obtain an estimate of urban population. A study was carried out in the city of Coimbatore (municipal area) using aerial photoghraphs of scale 1:4000 taken by a metric camera of 300 mm. focal length in the year 1979. The findings obtained by photo-interpretation compared very favourably with the interpolated population census figures for the year 1979, for the municipal area of the city Coimbatore. Dwelling units counted on the aerial photograph for different types of residential areas classified on the basis of size, shape and pattern are the physical indicators of population. Occupancy rate of dwelling units was determined by sampling survey carried out during field visit itself in this particular study.     

地形自适应车载LiDAR点云滤波

针对车载LiDAR点云进行地面点滤波时,基于常规TIN、坡度等滤波算法不能根据局部地形变化自动调整阈值的问题,该文结合城市点云特征和地形起伏度,提出地形自适应的车载LiDAR点云滤波方法。该方法通过引入地形自适应参数进行区域增长阈值的动态调整,实现地面点、非地面点的自动精确滤波。通过实测数据试验,结果表明该方法可适用于车载LiDAR城市点云中地面点和非地面点的较精确分类,解决低矮浅丘、低矮灌木等地物点不容易正确分类的问题。     

Reference data enhancement for geographic information retrieval using linked data

Gazetteers are instrumental in recognizing place names in documents such as Web pages, news, and social media messages. However, creating and maintaining gazetteers is still a complex task. Even though some online gazetteers provide rich sets of geographic names in planetary scale (e.g. GeoNames), other sources must be used to recognize references to urban locations, such as street names, neighborhood names or landmarks. We propose integrating Linked Data sources to create a gazetteer that combines a broad coverage of places with urban detail, including content on geographic and semantic relationships involving places, their multiple names and related non‐geographic entities. Our final goal is to expand the possibilities for recognizing, disambiguating and filtering references to places in texts for geographic information retrieval (GIR) and related applications. The resulting ontological gazetteer, named LoG (Linked OntoGazetteer), is accessible through Web services by applications and research initiatives on GIR, text processing, named entity recognition and others. The gazetteer currently contains over 13 million places, 140 million attributes and relationships, and 4.5 million non‐geographic entities. Data sources include GeoNames, Freebase, DBPedia and LinkedGeoData, which is based on OpenStreetMap data. An analysis on how these datasets overlap and complement one another is also presented.     

Graph theory for analyzing pair-wise data: application to geophysical model parameters estimated from interferometric synthetic aperture radar data at Okmok volcano,Alaska

Graph theory is useful for analyzing time-dependent model parameters estimated from interferometric synthetic aperture radar (InSAR) data in the temporal domain. Plotting acquisition dates (epochs) as vertices and pair-wise interferometric combinations as edges defines an incidence graph. The edge-vertex incidence matrix and the normalized edge Laplacian matrix are factors in the covariance matrix for the pair-wise data. Using empirical measures of residual scatter in the pair-wise observations, we estimate the relative variance at each epoch by inverting the covariance of the pair-wise data. We evaluate the rank deficiency of the corresponding least-squares problem via the edge-vertex incidence matrix. We implement our method in a MATLAB software package called GraphTreeTA available on GitHub (https://github.com/feigl/gipht). We apply temporal adjustment to the data set described in Lu et al. (Geophys Res Solid Earth 110, 2005) at Okmok volcano, Alaska, which erupted most recently in 1997 and 2008. The data set contains 44 differential volumetric changes and uncertainties estimated from interferograms between 1997 and 2004. Estimates show that approximately half of the magma volume lost during the 1997 eruption was recovered by the summer of 2003. Between June 2002 and September 2003, the estimated rate of volumetric increase is \((6.2 \, \pm \, 0.6) \times 10^6~\mathrm{m}^3/\mathrm{year} \). Our preferred model provides a reasonable fit that is compatible with viscoelastic relaxation in the five years following the 1997 eruption. Although we demonstrate the approach using volumetric rates of change, our formulation in terms of incidence graphs applies to any quantity derived from pair-wise differences, such as range change, range gradient, or atmospheric delay.     

信息隐藏技术在地理空间数据安全中的应用

地理空间数据安全是目前测绘领域急需解决的问题,信息隐藏技术为该问题的解决提供了一条新的思路。阐述信息隐藏的基本概念,讨论它在空间数据安全中两个重要的应用——空间数据水印技术及空间数据隐写技术,研究空间数据隐写技术的实现方法,并对这两种技术的异同进行比较。     

Using mobile laser scanning data for automated extraction of road markings

A mobile laser scanning (MLS) system allows direct collection of accurate 3D point information in unprecedented detail at highway speeds and at less than traditional survey costs, which serves the fast growing demands of transportation-related road surveying including road surface geometry and road environment. As one type of road feature in traffic management systems, road markings on paved roadways have important functions in providing guidance and information to drivers and pedestrians. This paper presents a stepwise procedure to recognize road markings from MLS point clouds. To improve computational efficiency, we first propose a curb-based method for road surface extraction. This method first partitions the raw MLS data into a set of profiles according to vehicle trajectory data, and then extracts small height jumps caused by curbs in the profiles via slope and elevation-difference thresholds. Next, points belonging to the extracted road surface are interpolated into a geo-referenced intensity image using an extended inverse-distance-weighted (IDW) approach. Finally, we dynamically segment the geo-referenced intensity image into road-marking candidates with multiple thresholds that correspond to different ranges determined by point-density appropriate normality. A morphological closing operation with a linear structuring element is finally used to refine the road-marking candidates by removing noise and improving completeness. This road-marking extraction algorithm is comprehensively discussed in the analysis of parameter sensitivity and overall performance. An experimental study performed on a set of road markings with ground-truth shows that the proposed algorithm provides a promising solution to the road-marking extraction from MLS data.     

地理空间数据结合手机信令等多源数据刻画城市居民出行特征

本文提出了以地理空间数据为支撑,结合手机信令、POI等多源数据刻画城市居民出行特征的方法。首先将信令数据与地理信息区块绑定,根据时间特征和地理区块的社会属性,识别居民的基本职住娱信息;然后综合民生POI点、出行特征拓展关键词、图谱等多源数据,运用工作日通勤分析模型和节假日出行特征提取模型,识别用户的通勤距离、通勤方式、日均通勤频次、周均工作时长、节假日出行场景、出行频次、驻留时长等内容,并形成涵盖职住娱信息的出行特征类标签集。以成都市为例,采集连续1个月的手机信令数据和同时期的POI等数据,验证了该方法的可行性,该成果作为反映城市实际人口规模数量和空间分布特征的城市人口地图大数据产品的重要内容,为政府部门、商企用户开展相关分析业务提供数据支撑。     

国家基础地理信息矢量数据的对象关系建模

本文总结了GIS空间数据模型的发展历程,通过对比分析当前主流的GIS数据模型的优缺点,指出对象关系型数据模型能够更好地组织和管理地理数据。并探索将对象关系型数据模型应用到国家基础地理信息数据管理和利用中,提出全国1∶100万数据库模型,并以政区为例证明该模型可以对空间数据进行有效地组织管理。     

空间信息可视化挖掘研究

空间信息的可视化挖掘是数据挖掘领域的热点 ,具有很强的应用前景。本文从数据挖掘的基本概念入手 ,详细介绍了可视化数据挖掘的两种分类体系 :Keim分类体系和Card分类体系 ,同时分析了这两种分类体系中各种可视化数据挖掘方法的基本思路 ,探讨了可视化数据挖掘技术与空间信息领域应用相结合的各种途径 ,并给出了空间信息可视化挖掘的常用方法     

An automated algorithm for extracting road edges from terrestrial mobile LiDAR data

Terrestrial mobile laser scanning systems provide rapid and cost effective 3D point cloud data which can be used for extracting features such as the road edge along a route corridor. This information can assist road authorities in carrying out safety risk assessment studies along road networks. The knowledge of the road edge is also a prerequisite for the automatic estimation of most other road features. In this paper, we present an algorithm which has been developed for extracting left and right road edges from terrestrial mobile LiDAR data. The algorithm is based on a novel combination of two modified versions of the parametric active contour or snake model. The parameters involved in the algorithm are selected empirically and are fixed for all the road sections. We have developed a novel way of initialising the snake model based on the navigation information obtained from the mobile mapping vehicle. We tested our algorithm on different types of road sections representing rural, urban and national primary road sections. The successful extraction of road edges from these multiple road section environments validates our algorithm. These findings and knowledge provide valuable insights as well as a prototype road edge extraction tool-set, for both national road authorities and survey companies.     

Indirect approach to invariant point determination for SLR and VLBI systems: an assessment

We assess the accuracy of some indirect approaches to invariant point (IVP), or system reference point, determination of satellite laser ranging (SLR) and very long baseline interferometry (VLBI) systems using both observed and simulated survey data sets. Indirect IVP determination involves the observation of targets located on these systems during specific rotational sequences and by application of geometrical models that describe the target motion during these sequences. Of concern is that most SLR and VLBI systems have limited rotational freedom thereby placing constraint on the reliability of parameter estimation, including the IVP position. We assess two current approaches to IVP analysis using survey data observed at the Yarragadee (Australia) SLR and the Medicina (Italy) VLBI sites and also simulated data of a large rotationally constrained (azimuth-elevation) VLBI system. To improve reliability we introduce and assess some new geometric conditions, including inter-axis, inter-circle and inter-target conditions, to existing IVP analysis strategies. The error component of a local tie specifically associated with the indirect determination of SLR and VLBI IVP is less than 0.5 mm. For systems with significant rotational limits we find that the inter-axis and inter-circle conditions are critical to the computation of unbiased IVP coordinates at the sub-millimetre level. When the inter-axis and inter-circle geometric conditions are not imposed, we retrieve biased vertical coordinates of the IVP (in our simulated VLBI system) in the range of 1.2–3.4 mm. Using the new geometric conditions we also find that the axis-offset estimates can be recovered at the sub- millimetre accuracy (0.5 mm).     

面向林地信息提取的 Pleiades-1影像融合算法评价分析

以Pleiades-1影像为对象,以探究其面向林地信息提取的融合算法选择为视角,通过基于目视和定量特征分析、辅助面向对象分类分析的方法,为林业部门遥感影像大规模融合应用提供参考。研究认为Pansharp和GramSchmidt算法融合结果目视效果良好,各波段与原多光谱相关系数均高达0.8以上,清晰度与纹理增强明显。两种融合算法影像在不同林地层次信息提取能力各有优势,Pansharp融合结果在林地层次分类总精度可达86.55%,Gram-Schmidt融合结果则在森林类型层次具有最高的分类总精度78.76%。具体融合算法的选取需根据其应用的信息提取层次而定。     

Synergetic use of remote sensing and geophysical data for exploration of porphyry copper deposits, using GIS

Darrehzar porphyry copper deposit is situated in the Urumieh-Dokhtar magmatic assemblage of central Iran. In this paper, the integration of multiple geodata sets has been carried out using geographic information system for mapping lithology or hydrothermally altered rocks and also in selecting the best discriminating data elements for exploration of porphyry copper deposits located in areas with similar geological setting and climatic conditions. Principal component analysis is found useful for reducing large data sets into a few principal components. The integration of various geophysical data with SPOT image data through GIS has shown that the hydrothermal alteration and lithology can be mapped with more efficiency.