基于双目视觉的无人机编队相对定位算法

针对无人机编队飞行时双目视觉定位精确性差、计算量大、实时性不高的技术现状,对基于特征点的FAST定位和BRIEF旋转(Oriented fast and rotated brief,ORB)算法进行了改进,提出了一种适用于无人机双目视觉定位的算法。在改进ORB算法中,采用提取目标区域、最近邻约束和随机抽样一致(Random sampling consensus,RANSAC)方法,提高了特征点提取与匹配效率,也提高了特征点匹配质量;对于双目视觉定位,提出了适用条件更加宽泛的双目视觉定位模型,并保证了模型的定位精度;最后使用卡尔曼滤波算法对无人机的定位信息进行估计,进一步提高了无人机的定位精度。实验表明,算法具有较高的精确性和实时性,满足无人机间的相对定位要求。     

嫦娥三号着陆器统计定位精度分析

“嫦娥三号”将在月球放置着陆器,实现月面软着陆,因此,需要对着陆器进行精确定位.本文简述了月球着陆器的统计定位方法与协方差分析理论,分析了影响统计定位精度的主要误差源.基于现有测控条件,从跟踪弧段和测量数据组合2个方面,对“嫦娥三号”着陆器的定位精度进行了分析.针对短弧条件下单站测距数据定位不稳键的问题,提出了结合月面高程约束的定位方法.协方差分析结果表明：高程数据的使用可以实现单站30 min测距优于1 km的定位精度;当观测数据累积至3d时,单站测量与VLBI（Very Long Baseline Interferometry,甚长基线干涉测量）的不同组合可以实现同等量级、优于百m的定位精度;测量系统差是制约定位精度的主要因素,完全标校测量的系统偏差则能实现10 m左右的定位精度.     

天象一号低轨导航增强系统研究与在轨试验验证

如何实现GNSS全球瞬时高精度服务一直是GNSS领域的迫切需求和研究热点.采用低轨导航增强技术体制,利用低轨卫星运动几何变化快的特点,解决GNSS精密单点定位快速收敛问题和性能提升问题,是GNSS高精度定位服务未来发展的重要方向.从全球瞬时高精度服务内涵出发,阐述了天象一号低轨导航增强试验系统的技术体制,包括系统工作模...     

Categorical Bias in Line Angle Judgments: Sex Differences and the Use of Multiple Categories

According to the Category Adjustment (CA) model, spatial estimates (e.g., of location) involve Bayesian combination across multiple, hierarchical pieces information, each weighted by its relative certainty. Recent work, though, has shown that men and women differ in terms of their certainty regarding fine-grained and categorical information in location memory. Here we demonstrate that this reflects a more general sex difference in visuospatial processing by examining bias patterns in a line angle judgment task (JLAP-15). In addition, the data suggest that multiple, hierarchical levels of categorical information influenced spatial judgments. These results imply that the hierarchical combination outlined by the CA model extends beyond two levels, and that men and women apply differential weighting to these representations.     

Stochastic modelling considering ionospheric scintillation effects on GNSS relative and point positioning

Global Navigation Satellite Systems (GNSS), in particular the Global Positioning System (GPS), have been widely used for high accuracy geodetic positioning. The Least Squares functional models related to the GNSS observables have been more extensively studied than the corresponding stochastic models, given that the development of the latter is significantly more complex. As a result, a simplified stochastic model is often used in GNSS positioning, which assumes that all the GNSS observables are statistically independent and of the same quality, i.e. a similar variance is assigned indiscriminately to all of the measurements. However, the definition of the stochastic model may be approached from a more detailed perspective, considering specific effects affecting each observable individually, as for example the effects of ionospheric scintillation. These effects relate to phase and amplitude fluctuations in the satellites signals that occur due to diffraction on electron density irregularities in the ionosphere and are particularly relevant at equatorial and high latitude regions, especially during periods of high solar activity. As a consequence, degraded measurement quality and poorer positioning accuracy may result.     

空间谱估计经典算法性能比较

空间谱估计是阵列信号处理的一个重要研究方向。空间谱估计理论与技术已日趋成熟，近几十年的经典谱估计技术包括：常规波束形成（CBF）、Capon谱估计、多重信号分类（MUSIC）、旋转不变子空间算法（ESPRIT）、最大似然（ML）、子空间拟合（SF），及这些算法的扩展和变形。上述算法在各个分散的文章中均有具体深入的理论分析和研究，亦有类似的2种或3种算法的性能比较，但是针对这些所有算法的性能比较，就笔者所知尚无公开报道，而使工程实现时对算法的选择没有依据。本文对这些经典算法做了简介，列出各个算法的优缺点，并对性能进行仿真比较，能直观地得到各个算法的性能对比，给工程实现算法选择提供理论依据。     

一种GPS定位信息可用性的实时判定方法

基于GPS接收机输出数据,采用3级AR模型来预测下一时刻的GPS输出值,并与实际的输出值相比较,以一定的检测门限,判断当前时刻定位信息的可用性。通过仿真证明该方法的有效性,为GPS的可用性判定提供了一种方法。     

Environmental reference systems for large-scale spaces

Human navigation in well-known environments is guided by stored memory representations of spatial information. In three experiments (N = 43) we investigated the role of different spatial reference systems when accessing information about familiar objects at different locations in the city in which the participants lived. Our results indicate that two independent reference systems underly the retrieval of spatial knowledge. Environmental characteristics, e.g., the streets at an intersection, determine which headings are easier to imagine at a given location and lead to differences in accessibility of spatial information (orientation-specific behavior). In addition, access to spatial information depends on the relative direction of a location with respect to the imagined heading, such that information about locations imagined in front of oneself is easier to access than about locations towards the back. This influence of an egocentric reference system was found for environmental knowledge as well as map-based knowledge. In light of these reference system effects, position-dependent models of spatial memory for large-scale environments are discussed. To account for the simultaneous effect of an environmental and an egocentric reference system, we present a 2-level model of spatial memory access.     

基于北斗接收机的车载卫星导航系统的设计

基于北斗卫星导航系统、北斗地基增强系统、移动通信网络,设计开发了 一款小体积、高精度车载导航系统。主要在接收基站差分信息以及实现高精度定位方面 进行探索。通过单点定位和差分定位的野外跑车对比试验得出,该系统性能稳定、可靠 性高,其差分定位精度能够满足车辆导航的要求。     

基于火箭橇的北斗动态定位精度鉴定方法

介绍了几种现有的以GPS/北斗为主要代表的卫星导航系统的动态定位精度 鉴定方法,分析了这几种方法在模拟实际使用环境、鉴定精度等方面的优缺点,提出了 一种基于火箭橇试验平台的北斗导航定位系统动态定位精度鉴定方法。该方法能够很好 地模拟北斗导航定位系统实际工作环境（速度、加速度、振动和天线角度等）,解决高 动态、高精度北斗导航定位系统动态定位精度鉴定问题,并对该方法的原理和实施方法 作了详细的论述,最后分析了该方法的不确定度及误差,并提出了改进措施。