Rigorous mathematical models for the densification and integration of geodetic networks

Existing position information in a network can be integrated with the densification solution in two ways: One way is to obtain a solution of the densification network followed by a merger of this and all other solutions or vice versa. Alternatively, the existing solutions (not used as weighted constraints) can be taken to be pseudo-observations in a simultaneous adjustment with the “new” observations. In both cases, all existing solutions must first be transformed to the coordinate system of the densified network and be statistically compatible with it. Simultaneous densification and integration is discussed through mathematical adjustment models in which the geometrical strength of networks is underscored. The rationale behind densifying and integrating networks either in two different steps or simultaneously is analyzed. It is concluded that the simultaneous approach should be avoided unless the various solutions turn out to be statistically compatible.     

GPS动态测量连续周跳检验

本文针对ＧＰＳ动态测量中经常出现的连续周跳,提出了一种新的连续周跳的检验方法。该方法在理论上是最优的,与Ｋａｌｍａｎ滤波平行操作,能够实行处理周跳引起的偏差;而且,在偏差估计的同时,兼顾后续偏差检验,因而可利用尽可能多的观测历元信息来获取精度较高的偏差估值。实例计算表明,该方法在应用中是很有效的。     

ROAD-SURVEYING IN THE EAST

Abstract

The title of this article is wide and generous, covering the art of road-surveying under every condition of climate from snow to tropical heat and in all types of country from moist forest to arid desert, from wooded mountains to barren rocks. But there is one feature that is common to all these conditions. Skilled supervision is at a minimum, and semi-skilled subordinates do the work. This has naturally had an influence on the quality and extent of the surveying carried out as a preliminary to the making of new roads. Some junior official, frequently from a subordinate service, is detailed for a survey, and he is expected to locate the final centre-line of the road on the ground and to produce plans, sections and a complete construction estimate. How then does he set about it? He probably has a small-scale map—in India, if he is lucky, a good, contoured, one-inch-to-the-mile map; and there are almost certain to be village tracks, either cart-tracks or man-tracks. Further, there will be certain obligatory points on the route, a pass to be crossed, a river to be bridged in a particular neighbourhood where it has well-defined banks, a town or village to be served, and so on.     

基于空间统计学的空间数据窗口大小的确定

提出基于空间统计学的方法来确定空间数据窗口大小,实例证明是可行的。同时提出了对海底照片成像不均匀光照进行纠正的思路和方法，该方法简单有效，效果较理想。     

基于FFT的快速SAR分布目标回波模拟算法

大面积分布目标的合成孔径雷达 (SAR)回波模拟需要大量的运算 ,文中提出了一种合成孔径雷达回波模拟的快速算法 ,算法利用时域插值和FFT来缩减运算量 ,对于大面积目标回波模拟时 ,该算法有很高的效率。文中详细分析sinc函数插值所带来的误差以及补偿方法 ,并在次基础上提出了一种利用增采样插值方法 ,该方法以增加少量运算为代价 ,使得模拟精度的大幅度提高。文中比较了传统方法和基于FFT的快速SAR分布目标回波模拟算法的模拟结果 ,证明了这种快速算法确实行之有效     

测量平差中不适定问题解的统一表达与选权拟合法

将测量平差中常见的几种数学模型分析比较,发现它们的解可以统一表达,形式上,都可以由吉洪诺夫正则化原理导出.在拟稳平差思想的启迪下,作者提出选权拟合法解不适定问题的思路.作者强调,解不适定问题应根据具体问题对参数作具体分析,找出合理的权阵或参数约束矩阵,利用统一的解式,可以得到符合客观实际的结果.最后介绍两个新解法算例.     

TESTING A THEODOLITE FOR ACCURACY

Abstract

When a theodolite is used to measure an angle, the result will be subjected to certain instrumental and personal errors which affect the measurement. Such errors may be accidental or systematic. Those of the former type, which follow no law and which may with equal probability occur at any graduation, are more easily eliminated, since, if a very large number of readings is taken, it is probable that the errors will cancel out and that the mean will approximate very closely to the correct figure. Systematic errors are usually due to instrumental defects and rnay be expressed as a function of the reading itself; it is the object of the manufacturer to eliminate these as far as possible, since cancellation by reiteration or by repetition is not to be expected wholly.     

略论我国国土资源面临的 主要问题和对策

我国国土资源现状面临严峻局面,耕地面积迅速减少,土地沙漠化迅速发展,森林资源蓄积量日益减少,国土资源污染日益严重,淡水资源贫乏,因此,必须对国土资源加强管理,成立综合管理部门,健全完善国土资源法规、管理办法和实施细则,制定并认真实施国土资源利用开发规划。为此,需建立国土资源遥感动态监测体系和建立自然灾害遥感实时监测系统,加快国土资源数据库的建设,以保证宏观决策的科学性和合理性。我国疆域辽阔,国土资源的空间分布、类型、结构和特征存在着明显的差别。由于地理位置和历史因素的影响,各地区国土资源开发利用的程度各不相同。随着生产活动的扩展和深化,加上自然灾害的影响,致使国土资源状况面临着日益严重的局面。     

Star and polyline glyphs in a grid plot and on a map display: which perform better?

Glyphs are small geometric shapes that in geovisualization are often used to represent multidimensional spatial data. The aim of this study is to investigate the effectiveness of their two types – star and polyline glyphs, as they can encode the same message and can provide similar functionality. Thus, if the two glyph types are similar and can be used for the same data, the question arises as to which of them better facilitates various user tasks. To address this question, an empirical study of 26 individual users is conducted to investigate differences in user performance for polyline and star glyphs shown either in a grid plot or on a map display. In this study, a task-based approach with eye-tracking is applied, as well as a subjective questionnaire and a psychological test of cognitive style. The finding is that polyline glyphs better facilitate tasks when datapoint values in glyphs are to be read, whereas star glyphs are better when a visual search among glyphs is to be done. Moreover, the results reveal that the map display works better than the grid plot. If star glyphs are to be used, the key (legend) needs to be better incorporated into a visual interface.     

The analytical continuation bias in geoid determination using potential coefficients and terrestrial gravity data

One important application of an Earth Gravity Model (EGM) is to determine the geoid. Since an EGM is represented by an external-type series of spherical harmonics, a biased geoid model is obtained when the EGM is applied inside the masses in continental regions. In order to convert the downward-continued height anomaly to the corresponding geoid undulation, a correction has to be applied for the analytical continuation bias of the geoid height. This technique is here called the geoid bias method. A correction for the geoid bias can also be utilised when an EGM is combined with terrestrial gravity data, using the combined approach to topographic corrections. The geoid bias can be computed either by a strict integral formula, or by means of one or more terms in a binomial expansion. The accuracy of the lowest binomial terms is studied numerically. It is concluded that the first term (of power H²) can be used with high accuracy up to degree 360 everywhere on Earth. If very high mountains are disregarded, then the use of the H² term can be extended up to maximum degrees as high as 1800. It is also shown that the geoid bias method is practically equal to the technique applied by Rapp, which utilises the quasigeoid-to-geoid separation. Another objective is to carefully consider how the combined approach to topographic corrections should be interpreted. This includes investigations of how the above-mentioned H² term should be computed, as well as how it can be improved by a correction for the residual geoid bias. It is concluded that the computation of the combined topographic effect is efficient in the case that the residual geoid bias can be neglected, since the computation of the latter is very time consuming. It is nevertheless important to be able to compute the residual bias for individual stations. For reasonable maximum degrees, this can be used to check the quality of the H² approximation in different situations.Acknowledgement The author would like to thank Prof. L.E. Sjöberg for several ideas and for reading two draft versions of the paper. His support and constructive remarks have improved its quality considerably. The valuable suggestions from three unknown reviewers are also appreciated.     

利用卫星轨道资料获取降水云团尺度的新方案

提出一种新的统计方案,以目标面积比为核心度量指标,并参照连续圆形目标定义目标面积比意义上的等效半径,实现对目标宏观尺度大小的量化估计。此方法能有效减轻轨道截断效应所造成的目标尺度低估,可对通过计数类方法得到的目标空间尺度做出有效修正。     

无验潮模式水下地形测量技术的研究

传统的水下地形测量模式定型于利用GPS测定水底点的平面位置,利用测深仪测定水底点的深度,附之以瞬时潮位资料,获得点位的高程.这种模式在上述条件具备的情况下,可取得完满的结果.但当验潮条件不具备时,该模式将不能获得测点的高程.为了弥补这一缺陷,简化工作流程,提高水下地形测量的精度,本文提出了一种无验潮模式下的水下地形测量思想,该思想不用专门测定潮位,而直接利用GPS的RTK测量技术,辅之以姿态测量和补偿,从而获得高精度的水底点高程.该方法被验证是正确的,希望进一步的推广应用.     

Eye on the Ionosphere: The Spatial Variability of Ionospheric Range Delay

The ionospheric range delay is highly variable both in space and in time. The ionospheric correlation distance is defined as the distance over which a measurement of the difference from monthly mean ionospheric range delay at one location can be used to determine the difference from mean conditions at a second location. The percentage improvement required is dependent upon the actual correlation coefficient, which must be relatively large to produce a significant improvement over differences from average conditions at two stations. Results of studies of the correlation distance show that, in order to obtain even a 28% improvement over monthly median conditions, the measurement location must be within approximately 3,000 km in longitude or 1,800 km in latitude from the location where the update from monthly mean conditions is required, at least in the mid-latitude region. Another study showed that, in order to be able to determine an improvement of 1 m in ionospheric range delay from average ionospheric conditions at a location remote from where the actual measurement of range delay is made, the measurement must be within approximately 500 km of that location. ? 2000 John Wiley & Sons, Inc.     

Efficiency of carrier-phase integer ambiguity resolution for precise GPS positioning in noisy environments

Precise GPS positioning relies on tracking the carrier-phase. The fractional part of carrier-phase can be measured directly using a standard phase-locked loop, but the integer part is ambiguous and the ambiguity must be resolved based on sequential carrier-phase measurements to ensure the required positioning precision. In the presence of large phase-measurement noise, as can be expected in a jamming environment for example, the amount of data required to resolve the integer ambiguity can be large, which requires a long time for any generic integer parameter estimation algorithm to converge. A key question of interest in significant applications of GPS where fast and accurate positioning is desired is then how the convergence time depends on the noise amplitude. Here we address this question by investigating integer least-sqaures estimation algorithms. Our theoretical derivation and numerical experiments indicate that the convergence time increases linearly with the noise variance, suggesting a less stringent requirement for the convergence time than intuitively expected, even in a jamming environment where the phase noise amplitude is large. This finding can be useful for practical design of GPS-based systems in a jamming environment, for which the ambiguity resolution time for precise positioning may be critical.     

基于SVG的矢量WebGIS实现技术研究

SVG是一种基于XML的用来描述二维矢量图形和矢量/栅格混合图形的标记语言,虽然SVG不是为了面向地理空间数据发布而制定的标准,但它的许多特性都能被广泛地应用到WebGIS中,从而实现矢量WebGIS。由于SVG通过简单的文本语句描述矢量图像,所以SVG通常数据量很小,并且SVG支持GZIP压缩,所以基于SVG构建WebGIS能减轻网络传输负载,加快地图显示速度。SVG内置了对JavaScript的支持,且SVG可通过DOM解析映像成内存中的树型结构,所以客户层可通过JavaScript对DOM的操作实现对地图的缩放、漫游、查询、图层控制等交互操作。     

变形信号与噪声的分离方法及其应用

在对变形体进行监测的时候会得到一系列不同时间的观测结果,比如对滑坡的位移监测,得到一系列的坐标,通过与首期观测数据的比较可获得变形量,然而测量中不可避免的含有误差,如何将变形信息和观测噪声分离是一个需要解决的问题。本文在变形是一个连续过程的假设下,以给定的验前方差为约束条件,通过三次连续逼近样条函数建立变形曲线,达到变形信号与噪声分离的目的,文中通过对某滑坡多年监测数据的分析验证了该方法的可行性。     

Monitoring Isostatic Rebound in Antarctica with the Use of Continuous Remote GPS Observations

A solar-powered GPS receiver has been installed near Beaver Lake, Antarctica, to monitor postglacial isostatic rebound that may be occurring as a result of ice thinning near the Lambert Glacier since the last glacial maximum. The equipment is 400 km from the nearest Australian Antarctic base and is completely automated. It is expected that there will be sufficient solar power to operate the equipment from January 1998 to May 1998, but the data will not be recovered until the following summer season. The scatter in height computed from the first 25 days of data is ± 7.5 mm. If such precision is representative of the accuracy of the height estimates, isostatic rebound of < 1 mm/yr will be able to be detected after a few years of observations at the site. ? 1999 John Wiley & Sons, Inc.     

DETERMINATION OF AZIMUTH AND LATITUDE FROM OBSERVATIONS OF A SINGLE UNKNOWN STAR BY A NEW METHOD

Abstract

The purpose of this paper is to describe a new and easy method of determining the (astronomical) latitude and azimuth at any place and to explain the line of approach and the formulae. It will be seen that the method should be useful to a wide circle of land surveyors. One of its principal advantages is that identification of the star is not necesssary and it can be used when no star chart or star catalogue is available.     

Photogrammetry and geographic information systems for quick assessment, documentation and analysis of earthquakes

After a catastrophe like an earthquake, one on the most important problems is to provide shelter and housing for the homeless. To this end, it is necessary to decide if a building is still habitable, or if it is has to be renovated or even torn down. A prerequisite for such decisions is the detailed knowledge about the status of the building. Earlier earthquakes revealed problems in the processes of documenting and analysing the building damage, as they demanded much effort in terms of time and manpower. The main difficulties appeared to be because of the analogue damage assessments which created a great variety of unstructured information that had to be put in a line to allow further analysis. Apart from that, documentation of damage effects was not detailed and could only be carried out on the spot of a disaster. The aim of this study is to make an improvement, using combination of Geographic Information Systems (GIS) as a management and data analysis tool and photogrammetry as a documentation method. Photogrammetric data acquisition is achieved using a CCD camera and the digital photogrammetric software package PICTRAN by Technet. The information system part is the GIS package ArcView by ESRI. The combination of rapid data acquisition and GIS offers a quick assessment of the situation and the possibility of its objective and holistic analysis. This is the prerequisite for a quick initiation of appropriate measures to help people.     

Efficient Directional Gaussian Smoothers

Linear and nonlinear filters, including morphological operators, play a significant role in the processing of remote sensing imagery. In particular, smoothing filters have been extensively used for noise removal and image restoration. In applications where linear and shift-invariant filters can be effectively employed, filtering is computationally efficient if implemented in transform domains. Nevertheless, in remote sensing applications, it is essential that smoothing filters be capable of handling missing and erroneous data without loss of information. In such cases, filtering requires the involvement of logical operations in order to determine which pixels should be used for processing, and thus takes the form of a nonlinear operator. Hence, transform-based methods cannot be used. Still, in applications where large volumes of data need to be processed, it is greatly desired that fast filtering algorithms are used. This letter introduces a computationally efficient spatial-domain-based implementation which is partially separable and steerable. The technique is general, and its efficiency has been demonstrated on weather radar data. It is shown that the proposed filtering approach is significantly faster compared to a recently introduced separable filter implementation.