Cycle graph analysis for 3D roof structure modelling: Concepts and performance

The paper presents a cycle graph analysis approach to the automatic reconstruction of 3D roof models from airborne laser scanner data. The nature of convergences of topological relations of plane adjacencies, allowing for the reconstruction of roof corner geometries with preserved topology, can be derived from cycles in roof topology graphs. The topology between roof adjacencies is defined in terms of ridge-lines and step-edges. In the proposed method, the input point cloud is first segmented and roof topology is derived while extracting roof planes from identified non-terrain segments. Orientation and placement regularities are applied on weakly defined edges using a piecewise regularization approach prior to the reconstruction, which assists in preserving symmetries in building geometry. Roof corners are geometrically modelled using the shortest closed cycles and the outermost cycle derived from roof topology graph in which external target graphs are no longer required. Based on test results, we show that the proposed approach can handle complexities with nearly 90% of the detected roof faces reconstructed correctly. The approach allows complex height jumps and various types of building roofs to be firmly reconstructed without prior knowledge of primitive building types.     

基于机载 Lidar 的地貌数据快速更新方案研究

空间地理信息作为国家信息资源的重要组成部分之一,承担着越来越重要的作用,地貌数据作为空间数据的组成部分,其数据采集及更新十分重要。机载 Lidar 问世以来受到测绘行业广泛重视,其应用不断扩展。该文以地貌数据的快速更新为研究目的,深入分析了地貌更新流程以及机载 Lidar 数据成果,并在此之上提出基于机载 Lidar 数据的地貌快速更新方案,研究其具体步骤以及核心技术,同时采用 CAD 二次开发实现地貌更新数据预处理,大幅提高地貌更新效率。     

Precise and Accurate In Situ Determination of Lead Isotope Ratios in NIST,USGS, MPI‐DING and CGSG Glass Reference Materials using Femtosecond Laser Ablation MC‐ICP‐MS

Lead isotope ratio data were obtained with good precision and accuracy using a 266 nm femtosecond laser ablation (fLA) system connected to a multi‐collector ICP‐MS (MC‐ICP‐MS) and through careful control of analytical procedures. The mass fractionation coefficient induced by 266 nm femtosecond laser ablation was approximately 28% lower than that by 193 nm excimer laser ablation (eLA) with helium carrier gas. The exponential law correction method for Tl normalisation with optimum adjusted Tl ratio was utilised to obtain Pb isotopic data with good precision and accuracy. The Pb isotopic ratios of the glass reference materials NIST SRM 610, 612, 614; USGS BHVO‐2G, BCR‐2G, GSD‐1G, BIR‐1G; and MPI‐DING GOR132‐G, KL2‐G, T1‐G, StHs60/80‐G, ATHO‐G and ML3B‐G were determined using fLA‐MC‐ICP‐MS. The measured Pb isotopic ratios were in good agreement with the reference or published values within 2s measurement uncertainties. We also present the first high‐precision Pb isotopic data for GSE‐1G, GSC‐1G, GSA‐1G and CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5 glass reference materials obtained using the femtosecond laser ablation MC‐ICP‐MS analysis technique.     

基于试验的模拟月壤表层取样理论修正及其应用

月球探测对于我国各方面综合实力的提升均具有巨大的推动作用。当前我国各研发机构对月球采样的研发重点集中于采样机具的设计制造上,对采样机具和月壤之间相互作用却研究较少。与地球土壤相比,月壤的形成环境与条件完全不同,从而造就了其较为特殊的物理力学性质。在利用与真实月壤类似的模拟月壤进行的薄壁圆筒贯入试验中,发现存在月壤滞留和月壤附壁现象,从而分析得出在采样机具表面与月壤相互作用的理论分析中,除了传统的摩擦力理论外,还可通过最大抗剪强度进行分析。通过对试验现象和数据对比摩擦力理论和最大抗剪强度理论发现,最大抗剪强度理论更加符合实际情况。故将最大抗剪强度理论引入已有的月球螺旋钻进采样的理论模型中,通过计算得出基于最大抗剪强度理论计算的螺旋临界转速低于基于摩擦力理论计算的临界转速,在一定程度上能够降低采样机具的能耗。     

Correlation analysis and partial least square modeling to quantify typical minerals with Chang＇E-3 visible and near-infrared imaging spectrometer＇s ground validation data

In 2013, Chang＇E-3 program will develop lunar mineral resources in-situ detection. A Visible and Near-infrared Imaging Spectrometer （VNIS） has been selected as one payload of CE-3 lunar rover to achieve this goal. It is critical and urgent to evaluate VNIS＇ spectrum data quality and validate quantification methods for mineral composition before its launch. Ground validation experiment of VNIS was carried out to complete the two goals, by simulating CE-3 lunar rover＇s detection environment on lunar surface in the laboratory. Based on the hyperspectral reflectance data derived, Correlation Analysis and Partial Least Square （CA-PLS） algorithm is applied to predict abundance of four lunar typical minerals （pyroxene, plagioclase, ilmenite and olivine） in their mixture. We firstly selected a set of VNIS＇ spectral parameters which highly correlated with minerals＇ abundance by correlation analysis （CA）, and then stepwise regression method was used to find out spectral parameters which make the largest contri- butions to the mineral contents. At last, functions were derived to link minerals＇ abundance and spectral parameters by partial least square （PLS） algorithm. Not considering the effect of maturity, agglutinate and Fe~, we found that there are wonderful correlations between these four minerals and VNIS＇ spectral parameters, e.g. the abundance of pyroxene correlates positively with the mixture＇s absorption depth, the value of absorption depth added as the in- creasing of pyroxene＇s abundance. But the abundance of plagioclase correlates negatively with the spectral parame- ters of band ratio, the value of band ratio would decrease when the abundance of plagioclase increased. Similar to plagioclase, the abundance of ilmenite and olivine has a negative correlation with the mixture＇s reflectance data, if the abundance of ilmenite or olivine increase, the reflectance values of the mixture will decrease. Through model validation, better estimates of pyroxene, plagioclase and ilmenite＇s abundances are given. It is concluded that VNIS has the capability to be applied on lunar minerals＇ identification, and CA-PLS algorithm has the potential to be used on lunar surface＇s in-situ detection for minerals＇ abundance prediction.     

三维激光扫描仪在复杂环境中的应用

随着扫描仪性能的不断提升和对环境适应性的增强,在许多常规测量无法完成的情况下,借助其非接触、远距离测量的特点,可以在特殊环境下完成许多常规测量无法完成的任务。     

地面三维激光扫描点云数据精度影响因素及控制措施

地面三维激光扫描技术虽然具有分辨率高、准确度高、效率高等特点,但在应用过程中存在一系列影响三维激光扫描精度的因素。文中详细分析扫描距离、物体表面材质、控制网、标靶测量精度、光斑大小、扫描点间距、点云拼接精度、全反射物质和外界环境等因素对三维激光扫描精度的影响,并提出对以上影响因素的控制方法。     

机载激光雷达系统定位精度分析

从机载激光雷达系统误差的产生机制出发,分别对姿态角误差、DGPS误差、瞬时扫描角误差、激光测距误差对激光脚点定位精度的影响进行定量的分析,从理论上分析了机载激光雷达系统的定位精度。本文的结果对实际应用具有重要的参考价值。     

基于EPS平台的地面三维激光扫描点云数据处理方法探讨

三维激光扫描技术是通过大量密集的扫描点,以模拟形式体现目标实体对象表面丰富的形体信息,不能获取的点云数据直接读取目标对象的矢量化信息,并进行点云数据处理。笔者在工作中,以EPS2008软件平台为基础,利用VBScript脚本进行二次开发,实现了点云数据分层提取、点云线状地物提取、点云特征轮廓提取、点云数据断面提取和点云高程提取等功能。本文针对已经实现的功能进行探讨,指出每种方法的特点和应用范围。     

Weak stability boundary trajectories for the deployment of lunar spacecraft constellations

Suitable lunar constellation coverage can be obtained by separating the satellites in inclinations and node angles. It is shown in the paper that a relevant saving of velocity variation ΔV can be achieved using weak stability boundary trajectories. The weakly stable dynamics of such transfers allows the separation of the satellites from the nominal orbit to the required orbit planes with a small amount of ΔV. This paper also shows that only one different set of orbital parameters at Moon can be reached with the same ΔV manoeuvre starting from a nominal trajectory and ending at a fixed periselenium altitude. In fact, such a feature is proved to be common to other simpler dynamical systems, such as the two- and three-body problems.