A general-purpose framework for parallel processing of large-scale LiDAR data

ABSTRACT

Light detection and ranging (LiDAR) data are essential for scientific discoveries such as Earth and ecological sciences, environmental applications, and responding to natural disasters. While collecting LiDAR data over large areas is quite possible the subsequent processing steps typically involve large computational demands. Efficiently storing, managing, and processing LiDAR data are the prerequisite steps for enabling these LiDAR-based applications. However, handling LiDAR data poses grand geoprocessing challenges due to data and computational intensity. To tackle such challenges, we developed a general-purpose scalable framework coupled with a sophisticated data decomposition and parallelization strategy to efficiently handle ‘big’ LiDAR data collections. The contributions of this research were (1) a tile-based spatial index to manage big LiDAR data in the scalable and fault-tolerable Hadoop distributed file system, (2) two spatial decomposition techniques to enable efficient parallelization of different types of LiDAR processing tasks, and (3) by coupling existing LiDAR processing tools with Hadoop, a variety of LiDAR data processing tasks can be conducted in parallel in a highly scalable distributed computing environment using an online geoprocessing application. A proof-of-concept prototype is presented here to demonstrate the feasibility, performance, and scalability of the proposed framework.     

Assemblage characteristics of clay minerals and its implications to evolution of eolian dust input to the Parece Vela Basin since 1.95 Ma

To understand the provenance and evolution of eolian input in the last 1.95 Ma in the Parece Vela Basin in the eastern Philippine Sea, the clay mineral assemblage of a gravity core PV090510 from the basin was investigated using paleogeomagnetic dating and X-ray diffraction. The assemblage of the core mainly consisted of smectite （-46%） and illite （-40%）, with some chlorite （-10%） and kaolinite （-4%）. Analysis of the provenance of these minerals suggested that smectite was mainly derived from volcanic rocks of the Mariana Arc, while illite, chlorite, and kaolinite were mainly transported as eolian dust by the East Asian monsoon from central Asia. We used the ratio of （illite＋chlorite＋kaolinite）/smectite as a proxy for Asian eolian input to the Parece Vela Basin since 1.95 Ma. This ratio followed glacial and interglacial cycles and was consistent with the intensity of the East Asian monsoon and aridity of central Asia since 1.95 Ma. The changes of the ratio reflected three different stages of the East Asian monsoon and provenance climate.     

山体效应对台湾常绿阔叶林分布上限的影响

山体效应使山体内部的垂直植被带相对升高,影响山地的立体生态格局.台湾岛中央山脉在3500m以上,山地植被的分布高度不仅受到纬度和季风的影响,也必然受到山体效应的影响.采用台湾生物多样性信息中心发布的数据,利用多元线性回归模型分析纬度、山体效应(以山体基面高度为简单量化指标)以及季风(以冬雨量占全年降水量百分比为简明代表)对台湾常绿阔叶林分布上限的影响.结果表明,纬度、山体效应和季风为自变量的线性回归模型R2为0.562,回归方程显著,具有统计学意义,三个变量的贡献率分别为26.32％、64.12％与9.56％.这表明山体效应对台湾山地垂直带的影响非常显著,远远超过了纬度与季风的作用.同时还发现,冬雨量与垂直带分布高度的相关性以24.13°N为界,南北完全相反.该纬度以南,冬雨量与垂直带分布高度呈现较强的正相关性;而在以北,正相关性显著下降甚至出现了一定的负相关.后者应该与冬雨量过多有密切关系.     

An active crawler for discovering geospatial Web services and their distribution pattern – A case study of OGC Web Map Service

The increased popularity of standards for geospatial interoperability has led to an increasing number of geospatial Web services (GWSs), such as Web Map Services (WMSs), becoming publicly available on the Internet. However, finding the services in a quick and precise fashion is still a challenge. Traditional methods collect the services through centralized registries, where services can be manually registered. But the metadata of the registered services cannot be updated timely. This paper addresses the above challenges by developing an effective crawler to discover and update the services in (1) proposing an accumulated term frequency (ATF)–based conditional probability model for prioritized crawling, (2) utilizing concurrent multi-threading technique, and (3) adopting an automatic mechanism to update the metadata of identified services. Experiments show that the proposed crawler achieves good performance in both crawling efficiency and results' coverage/liveliness. In addition, an interesting finding regarding the distribution pattern of WMSs is discussed. We expect this research to contribute to automatic GWS discovery over the large-scale and dynamic World Wide Web and the promotion of operational interoperable distributed geospatial services.     

基于公众咨询的深圳公共气象服务需求特点分析

以2010—2013年深圳市气象局门户网站"业务咨询"板块公众咨询信息和深圳国家基本气象站观测资料为基础,从咨询量的时间变化规律、与多种气象因素的关联性等角度,对公共气象服务需求的特点进行分析,以揭示公众的公共气象服务需求在时间和要素上存在的规律和特征。结果表明:1)汛期是一年中市民最为关注天气的时段,周三和周五是一周内公众气象信息需求最大的时段;汛期市民最关注的天气是台风,秋、冬季节市民更为关注气候预测信息。2)市民高度关注降水,其精细化和个性化预报仍有很大提升空间;对相对湿度的关注,主要源于对"回南天"等潮湿天气的关注;日照时数与公众咨询密切相关,但主要通过降水间接影响;市民较少咨询气温,但在炎热、寒冷天气下,气温与市民咨询量表现出明显的相关性。     

Precise orbit determination of the Fengyun-3C satellite using onboard GPS and BDS observations

The GNSS Occultation Sounder instrument onboard the Chinese meteorological satellite Fengyun-3C (FY-3C) tracks both GPS and BDS signals for orbit determination. One month’s worth of the onboard dual-frequency GPS and BDS data during March 2015 from the FY-3C satellite is analyzed in this study. The onboard BDS and GPS measurement quality is evaluated in terms of data quantity as well as code multipath error. Severe multipath errors for BDS code ranges are observed especially for high elevations for BDS medium earth orbit satellites (MEOs). The code multipath errors are estimated as piecewise linear model in \(2{^{\circ }}\times 2{^{\circ }}\) grid and applied in precise orbit determination (POD) calculations. POD of FY-3C is firstly performed with GPS data, which shows orbit consistency of approximate 2.7 cm in 3D RMS (root mean square) by overlap comparisons; the estimated orbits are then used as reference orbits for evaluating the orbit precision of GPS and BDS combined POD as well as BDS-based POD. It is indicated that inclusion of BDS geosynchronous orbit satellites (GEOs) could degrade POD precision seriously. The precisions of orbit estimates by combined POD and BDS-based POD are 3.4 and 30.1 cm in 3D RMS when GEOs are involved, respectively. However, if BDS GEOs are excluded, the combined POD can reach similar precision with respect to GPS POD, showing orbit differences about 0.8 cm, while the orbit precision of BDS-based POD can be improved to 8.4 cm. These results indicate that the POD performance with onboard BDS data alone can reach precision better than 10 cm with only five BDS inclined geosynchronous satellite orbit satellites and three MEOs. As the GNOS receiver can only track six BDS satellites for orbit positioning at its maximum channel, it can be expected that the performance of POD with onboard BDS data can be further improved if more observations are generated without such restrictions.     

GIS平台软件自动化测试框架

针对GIS平台软件规模不断增大导致的软件测试工作量加重,手工测试无法保证GIS平台软件高质量运行的问题,该文提出了一套适用于地理信息领域的软件自动化测试与监控管理体系。在分析GIS软件测试流程和需求的基础上,结合TeamCity、Sonar、WhiteBox等20多个管理软件,研发了适用于GIS软件的自动化测试和持续集成系统,构成了软件测试与监控的管理体系。这一自动化测试框架在GIS软件生产流程的应用表明,该框架可保障GIS平台软件的高效运行。     

动态CTM对腰椎管狭窄症的诊断意义

本文对２０例有姿势依赖性平状的腰椎管狭窄症病人进行腰椎屈、伸直位动态ＣＴＭ观察表明，当腰椎处在伸直位时中央锥管和侧隐窝的容积均减少，表现为硬膜囊矢状径、硬膜囊最大径、韧带关节间径和黄韧带夹角均有显著减少，关节突向间盘方向突出使得椎管的前外角狭窄、神经袖周围的游离间隙消失，神经根受到挤压、作者从ＣＴ解剖学的角度分析了椎管内各种组织结构的动态变化及其对硬膜囊和神经根的影响，提出脊柱伸展时黄韧短缩性增厚     

A scalable cyberinfrastructure solution to support big data management and multivariate visualization of time-series sensor observation data

This paper reports our research in developing a cyberinfrastructure platform to support multivariate visualization of data collected from distributed sensor network. Three new techniques were introduced in this platform: (1) a hybrid data caching strategy that takes advantages of a scalable and distributed time series database, OpenTSDB, to realize efficient data retrieval; (2) a hyper-dimensional data cube is established to map and translate multivariate and heterogeneous sensor data into a common data structure to support location-aware visual analysis; and (3) a data-driven visualization module is implemented to support interactive and dynamic visualization on a simulated virtual globe. A series of experiments were conducted to demonstrate the good runtime performance of the proposed system. We expect this work to make a major contribution to both the visualization building block development in cyberinfrastructure research and the advancement of visual presentation and analysis of sensor data in domain sciences.