西藏沙漠化普查的遥感手段及其成图精度估算

简要介绍了西藏自治区沙漠化普查中所采用的遥感手段,通过对各种遥感信息源的使用比较,详细阐述了普查工作中对沙漠化土地及其它土地类型的判读和解译,并且对本次普查结果进行了精度估算。结果表明,利用遥感手段进行沙漠化土地调查不仅具有现实意义,而且为进一步沙漠化的防治和监测工作提供了准确的数据基础。     

空间信息处理技术与农田地理信息系统的研究

为了满足实施精细农业定位作物管理中数据管理与分析的需要,在对空间信息处理技术研究的基础上设计开发了一个农田地理信息系统。系统除了具有农田信息管理与数据处理的功能以外,还提供了处理GPS数据与RS图像的功能,方便了3S(GIS、GPS、RS)技术的集成应用。文章介绍了系统中GPS数据的制图与平滑处理、地图坐标转换、RS图像的几何校正与坐标配准、空间插值分析以及农田信息统计和查询等主要的功能及其实现方法。在北京精准农业示范区的应用表明系统可以作为一种用于精细农业研究的数据分析与信息管理的工具。     

数控机床RTCP精度的分析

RTCP精度是五轴联动数控机床的重要精度指标.本文是基于西门子840D数控系统,结合航空大型结构件加工企业高档五轴数控加工中心的实际情况,分析并总结出一套数控机床RTCP精度的检验与补偿的方法.     

基于粗糙集理论的不完备数据分析方法的混合信息系统填补算法

为了提高基于粗糙集理论的不完备数据分析方法(ROUSTIDA)在实际应用中对包含离散型(如整型、字符串型、枚举型)、连续型(如浮点数表达)、缺失型属性的混合信息系统(HIS)数据的填补能力,提出了一种基于粗糙集理论的混合信息系统缺失值填补方法(RSHISMIA).首先,根据决策属性等价类划分思想并按照决策属性对混合信息...     

基于MATLAB环境的精确空投系统模型分析与仿真

在针对运动体运动规律仿真领域中,MathWorks公司推出的Matlab软件具有强大的功能。本文针对近年来国际上较为热门的"精确空投系统"进行了简化建模,并在Matlab/simulink环境中进行了仿真分析,得到了较为准确可靠的仿真结果。     

基于构件的软件开发方法中的若干经验

基于构件的软件开发方法提出了全新的开发模式,在研究与应用中都体现出多方面的理论及实践价值,能很好地保证软件功能性、开发效率、质量、可靠性和可移植性。然而在突破传统开发方式的过程中,许多软件开发组织也面临采用新方法所带来的观念、组织、技术、过程等方面的挑战。文章针对基于构件的软件开发过程中遇到的问题作了理论分析,提出了一系列指导性经验法则。     

Visual–inertial navigation for pinpoint planetary landing using scale-based landmark matching

Landing an autonomous spacecraft within 100 m of a mapped target is a navigation challenge in planetary exploration. Vision-based approaches attempt to pair 2D features detected in camera images with 3D mapped landmarks to reach the required precision. This paper presents a vision-aided inertial navigation system for pinpoint planetary landing called LION (Landing Inertial and Optical Navigation). It can fly over any type of terrain, whatever the topography. LION uses measurements from a novel image-to-map matcher in order to update through a tight data fusion scheme the state of an extended Kalman filter propagated with inertial data. The image processing uses the state and covariance predictions from the filter to determine the regions and extraction scales in which to search for non-ambiguous landmarks in the image. The image scale management process operates per landmark and greatly improves the repeatability rate between the map and descent images. A lunar-representative optical test bench called Visilab was also designed in order to test LION. The observability of absolute navigation performances in Visilab is evaluated with a model developed specifically for this purpose. Finally, the system performances are evaluated at a number of altitudes along with its robustness to off-nadir camera angle, illumination changes, a different map generation process and non-planar topography. The error converges to a mean of 4 m and a 3-RMS dispersion of 47 m at 3 km of altitude on the test setup at scale.     

A multi-level conceptual data reduction approach based on the Lukasiewicz implication

Starting from fuzzy binary data represented as tables in the fuzzy relational database, in this paper, we use fuzzy formal concept analysis to reduce the tables size to only keep the minimal rows in each table, without losing knowledge (i.e., association rules extracted from reduced databases are identical at given precision level). More specifically, we develop a fuzzy extension of a previously proposed algorithm for crisp data reduction without loss of knowledge. The fuzzy Galois connection based on the Lukasiewicz implication is mainly used in the definition of the closure operator according to a precision level, which makes data reduction sensitive to the variation of this precision level.     

半实物网络测试系统从时钟频率漂移影响分析

针对精确时钟协议(PTP)用于半实物网络仿真测试时难以实现精确系统同步的问题,研究从时钟频率漂移对PTP仿真系统同步性能的影响。建立了半实物网络环境下PTP系统模型和时钟模型,解析性推导出单向传输链路中Slave_n对主时钟的时延误差估计,得出从时钟模型时延误差表达式具有一致的加权结构,且各误差项都将累积并渗透到传输线路中,影响整个网络的同步精度。基于此,设计多种半实物网络仿真场景进行验证、分析和测试。仿真结果表明:单个从时钟频率漂移对系统同步精度影响甚微,但系统内从时钟均存在漂移或主时钟存在时间抖动的情况下,造成的同步误差是单个从时钟频率漂移时的10倍,会对系统同步精度产生严重的影响,研究成果能为半实物网络测试环境时钟部署策略提供重要参考。     

Image retrieval using efficient local-area matching

We present an efficient and accurate method for retrieving images based on color similarity with a given query image or histogram. The method matches the query against parts of the image using histogram intersection. Efficient searching for the best matching subimage is done by pruning the set of subimages using upper bound estimates. The method is fast, has high precision and recall and also allows queries based on the positions of one or more objects in the database image. Experimental results showing the efficiency of the proposed search method, and high precision and recall of retrieval are presented. Received: 20 January 1997 / Accepted: 5 January 1998