北斗／GPS双模定位中快速选星算法研究

采用双系统组合定位模式,导航接收机能在同一时刻接收到超过20颗可见星,大大增加了可见星的数量,能提供十分精准的定位。但可见星数量大幅度增加带来定位精度提升的同时也带来了大量的计算量,加上实际作业中的一些问题,都大大增加了选星时间。本文从GDOP与星座几何布局的关系出发,结合实际应用场景,提出了基于仰角和方位角排序的选星算法。该方法以满足定位要求为前提,根据可见星仰角排序初筛卫星,对不同仰角卫星进行合理的顶星选择,以卫星均匀分布为原则,将在理想情况和实际情况下寻找有效定位平衡点,以规避无效选星并减少计算量,从而大大减少选星时间,有效实现了在北斗和GPS双模定位中的快速选星。      

一种改进的组合导航系统选星算法

针对GPS,GLONASS,BDS组合导航系统定位中卫星的选择作了相关分析。首先用STK软件进行仿真,分析几何精度因子与卫星数的关系,得出组合导航系统最佳选星数;再根据卫星星座的空间几何分布,基于次优选星算法的成本函数模型,结合各导航系统卫星测量精度的差异性以及次优选星算法的峰值、不稳定特点,构建一种以卫星高度角和载噪比确定的加权成本函数模型,提出一种依据加权成本函数选星的分步次优加权选星算法。实验结果表明,该选星算法能近似到达最优选星算法的效果,计算负荷也相对较小,可满足导航定位解算精度和实时性要求。     

多星座实时导航中一种快速次优的选星方法

随着各国卫星导航系统的建设与完善,同一历元的可见卫星数目逐渐增加,如何对众多卫星进行选择以优化利用现有资源便显得迫切而重要。本文以获得满足设计要求的GDOP为前提,根据各时刻可见卫星数量的大小,选择适合的遮蔽仰角,以卫星空间构型的体积与GDOP关系为依据,引入计算几何学中解决三维点集的凸壳问题的增量算法,并结合导航卫星星座的自身特点,提出了对卫星位置坐标直接进行选择的一种快速次优的选星算法。实验结果表明,在GDOP满足要求且选星数较少的情况下,相对传统GDOP选星法大大减小了计算量,该方法简洁快速,能有效满足选星求解的实时性和精度要求。     

一种多系统组合导航快速选星方法

采用多卫星导航系统组合导航,定位精度和系统可靠性会大幅提升,但导航定位运算量也会成倍增长。为解决多系统组合导航定位精度与实时性之间的矛盾,提出一种新的选星方法。新方法不追求最小GDOP值,而是以满足导航定位精度的GDOP值为前提,结合模糊理论中隶属函数的思想,按卫星在星座中均匀分布为原则进行选星。推导伪距测量的误差模型,分析了GDOP与测量误差之间的关系。北斗、GPS和GLONASS三系统组合导航选星实验结果表明,在不超过3次求解GDOP值的情况下,新方法能以不小于98%的概率得到GDOP≤4。     

基于GDOP贡献值递推的自动天文选星算法

传统天文测量依赖人工选星,自动化程度不高,难以快速选出具有最优几何分布的恒星观测组合,因而存在测量效率低、定位精度易受作业员影响等突出问题.为此,提出一种基于GDOP贡献值递推的自动天文选星算法.首先,构建GDOP贡献值的数学模型,确定递推选星策略,实现自动化选星;其次,利用GDOP值定量评估恒星观测组合的几何分布特性...     

利用特征星进行快速天文定向

提出了利用特征星进行快速天文定向。借助星空模拟软件Stellarium构建了特征星星库,并结合天文定向中的主要误差源,研究了选星策略,提高了定向精度。实际观测实验表明,利用特征星快速定向的内符合精度可优于0.4",外符合精度可优于1.0"。     

北斗系统时差定位报告选星方法研究

北斗卫星导航系统提供的无线电测定服务解决了"何人、何时、何处"的相关问题,实现了定位报告和态势共享,是北斗系统与其他全球卫星导航系统竞争的一个优势。利用北斗系统的无线电导航服务,可以使无线电测定服务摆脱对高程库的依赖,提高定位精度。研究了北斗系统时差定位报告的原理及形成时差的中圆地球轨道卫星的选星方法。模拟分析了北斗系统时差定位报告位置精度衰减因子随用户及北斗系统中圆地球轨道卫星位置变化的情况,得出如下结论:位置精度衰减因子主要受中圆地球轨道卫星纬度影响,中圆地球轨道卫星位于70°~80°N时,位置精度衰减因子最小;北斗系统时差定位报告选星时,在符合观测条件下,应选择纬度较大的中圆地球轨道卫星。为实现快速选星,推导了粗略估计卫星纬度的方法,仅利用5个卫星轨道参数实现快速计算卫星的粗略纬度。     

北斗/GPS组合定位方法

随着北斗卫星导航系统的逐渐完善,有关北斗系统定位的研究越来越深入,为了对比分析北斗系统和全球定位导航系统(GPS)定位的差异性,充分利用北斗地球静止轨道卫星(GEO)和倾斜地球同步轨道卫星(IGSO)高轨道卫星的特殊性,本文提出一种新的组合选星方法,选取卫星数较少且Position Dilution of Precision(PDOP)最小的北斗/GPS组合,分别对比分析北斗系统、GPS系统及其组合系统在楼顶开放环境和楼间恶劣环境下的定位效果。实验结果表明:北斗比GPS有更加稳定的定位效果,依据本文组合选星方法,利用少量卫星即可获得较好的定位精度。     

实时等角距星图仿真技术

本文提出并研究了实时等角距星图仿真的万法,推导了相关公式,改进了圆视场搜索法应用于星图视场选星;编写了相应的实时等角距星图仿真程序,实现了任意时刻、任意观测地点的动态星图显示;并通过对实测数据的分析,给出了实时等角距星图的显示精度.     

GNSS多系统融合相对定位选星方案设计及精度分析

针对全球导航卫星系统(Global Navigation Satellite System,GNSS)多系统融合定位精度及解算效率的平衡问题,提出一种基于相对定位模型下的分区域快速选星算法.该方法首先基于相对定位原理,构建伪距双差观测模型,其次利用卫星的方位角进行区域划分,在不同系统和高度角的条件下选取空间分布均匀的卫...     

THE VARIATION OF THE ATMOSPHERIC COEFFICIENT OF REFRACTION WITH THE NATURE OF THE SOURCE OF LIGHT

Abstract

In working out vertical heights on the Akuse-Kete Krachi chain of triangulation in the Gold Coast a fairly considerable difference was found between values of the coefficient of refraction obtained from observations taken during the day and those taken at night, the mean values being 0.069 for daylight observations to heliographs and 0.087 for night observations to lamps. This difference no doubt is due mainly to the condition of the atmosphere during the day differing from its condition during the night rather than to any effect due to different sources of light. A new chain has recently been observed in Western Ashanti, and the index of refraction for the daylight observations again gave a lower value than that obtained from the night observations, the figures being 0.073 and 0.099 respectively. For the night work three different sources of light were used, hurricane lamps for short lines, Tilley vapour-pressure lamps for lines of intermediate length, and McCaw acetylene signalling lamps by Watts for long lines. It occurred, therefore, to the writer to examine the results to see if the mean values of the index of refraction showed any variations for the different light sources, since it seemed reasonable to suppose that the constitution of the light emitted from each source would be different and hence that the coefficient of refraction might vary.     

ON THE ESSENCE OF THE LANGUAGE OF THE MAP

The author continues development of his concept of cartography as the “language of the map,” an earlier paper of this subject appearing in translation in M.S.R.S., 1985, No. 1. Although the term language has been widely used to describe cartographic communication, current theory fails to incorporate aspects of the language which provide for a comprehensive understanding of its structure and function. In particular, the language of the map and its symbolic elements cannot be explained reflexively by methods and rules of symbol and map design, since these elements were developed not before but after the existence of the language. The language of the map thus is proposed as the mechanism which provides for replicability or duplication in the way a system of mapmaking-map use functions (under diverse conditions, purposes, historical periods, and levels of training of users) through its different methods, models, and norms. Translated from: Geografiya i prirodnyye resursy, 1985, No. 3, pp. 142-151.     

THE THEORY OF THE ANALYTICAL SOLUTION OF THE STEREOGRAM

The theory of the solution of the stereogram is developed from the condition that the vector triangle, formed by the base-line and the two rays from the perspective centre to a common model point, shall be in equilibrium. Using this approach the unique definition of a point in the model follows naturally from the solution of the relative orientation problem.     

试论地图形式美的规律

本文从六个方面阐述了地图形式美的规律性,最后进一步说明了其规律性与增强地图美感的关系。     

THE CALCULATION OF THE HEIGHT OF KILIMANJARO

Abstract

The observations to height Kilimanjaro were made from two ground stations, Domberg (5,081·6 ft.) and Lelatema (5,323.1 ft.) and from a point called Kibo near Kaiser Wilhelm Spitze which is regarded as the highest point on the crater rim. It was originally intended to include a third ground station, Kifaru, but it was discovered that the ice cap obstructed observations between this point and the top.     

利用卫星测高资料推求西北太平洋海域的海洋大地水准面

本文根据卫星测高数据和海面动力地形资料，绘制了不相上下北太平洋海域局部大地水准面的精细结构图，对解决卫星测高技术中大地水准面积和海面地形的可分性问题作了初步尝试。     

THE ADJUSTMENT OF TRIGONOMETRICAL LEVELS AND THE EVALUATION OF THE COEFFICIENT OF TERRESTRIAL REFRACTION

Abstract

This paper is written primarily with the object of ascertaining how other Colonies and Dominions deal. with the adjustment of their trigonometricallevels; further, since the greater part of Nigeria is now covered by a framework of levels of primary accuracy it is of interest to examine the results. Moreover, the evaluation of the coefficient of refraction, and from it the temperature lapse-rate, is of some importance in view of the recent publication of the War Office Aneroid Tables. These tables are based on a standard lapse-rate of temperature.     

THE WORK OF THE ORDNANCE SURVEY OF THE IRISH FREE STATE

Abstract

Up to 31st March 1922, the work in Ireland with regard to the revision and supply of Ordnance Survey Maps was governed by similar rules to those existing at the Ordnance Survey of Great Britain. No changes were made in the Irish Free State until the revision of Co. Waterford was completed on the 25-inch scale in 1923. It was then decided to depart from the usual procedure of taking up the work of the revision of Counties according to a cycle of years, and to revise those particular portions of the country in which extensive alterations had been carried out by reason of the division of properties by the Congested Districts Board and the Irish Land Commission. Accordingly, those portions of Counties Galway, Mayo and Roscommon which had undergone the greatest development were taken up for revision. In all eighty-nine sheets were specially revised and completed by 1928.     

THE APPLICATION OF THE GAUSS METHOD OF COLLIMATION TO THE ADJUSTMENT OF SURVEY INSTRUMENTS

Abstract

Gauss's method of collimation is usually given scant attention in survey text-books. The following notes are based on experiments carried out at Accra in making a collimation base, the collimator being a Watts 2I-inch self-adjusting level fitted with a parallelplate micrometer.     

THE NAMING OF THE STARS

Abstract

The order of the constellations in the following catalogue is that of the list in Ptolemy's “Almagest, except that the modern groups in the northern hemisphere are inserted after Ptolemy's northern and before his zodiacal constellations, while the modern groups in the southern hemisphere follow the last of his list. The constellation-name in italic capitals is the Latin form in general use. It is followed by the English translation where necessary and by the French and German versions. The Greek and Arabic names, with their authorities, are then given and translated where they differ in meaning from the Latin.