共查询到20条相似文献，搜索用时 62 毫秒
1.
Sun Haiyan Ph.D 《地球空间信息科学学报》2001,4(3):1-5
［1］Liu D J,Shi W Z,Tong X H,et al.Precision analysis and quality cont rol of GIS spatial data.Shanghai:Shanghai Publishing House of Scientific Documen ts,1999
［2］Chen X R,Fang Z B,Li G Y,et al.Non_parameter statistics.S hanghai:Shanghai Publishing House of Science and Technology,1989
［3］Li Q H,Tao B Z.Application of probability statistical theory in survey ing.Beijing:Beijing Publishing House of Surveying and Mapping,1982
［4］Sun H Y.p_norm distribution theory and its application in surveyin g data processing:[Ph.D Thesis].Wuhan:Wuhan Technical University of Surveying and Mapping,1995 相似文献
2.
J. Marshall 《Journal of Geodesy》2002,76(6-7):334-344
Several pre-analysis measures which help to expose the behavior of L
1 -norm minimization solutions are described. The pre-analysis measures are primarily based on familiar elements of the linear
programming solution to L
1-norm minimization, such as slack variables and the reduced-cost vector. By examining certain elements of the linear programming
solution in a probabilistic light, it is possible to derive the cumulative distribution function (CDF) associated with univariate
L
1-norm residuals. Unlike traditional least squares (LS) residual CDFs, it is found that L
1-norm residual CDFs fail to follow the normal distribution in general, and instead are characterized by both discrete and
continuous (i.e. piecewise) segments. It is also found that an L
1 equivalent to LS redundancy numbers exists and that these L
1 equivalents are a byproduct of the univariate L
1 univariate residual CDF. Probing deeper into the linear programming solution, it is found that certain combinations of observations
which are capable of tolerating large-magnitude gross errors can be predicted by comprehensively tabulating the signs of slack
variables associated with the L
1 residuals. The developed techniques are illustrated on a two-dimensional trilateration network.
Received: 6 July 2001 / Accepted: 21 February 2002 相似文献
3.
Distances between demand points and potential sites for implementing facilities are essential inputs to location-allocation
models. Computing actual road distances for a given problem can be quite burdensome since it involves digitalizing a network,
while approximating these distances by l
p
-norms, using for instance a geographical information system, is much easier. We may then wonder how sensitive the solutions
of a location-allocation model are to the choice of a particular metric. In this paper, simulations are performed on a lattice
of 225 points using the k-median problem. Systematic changes in p and in the orientation of the orthogonal reference axes are used. Results suggest that the solutions of the k-median are rather insensitive to the specification of the l
p
-norm.
Received: 12 October 1998/Accepted: 17 September 1999 相似文献
4.
Let there be given a twodimensional symmetric rank two tensor of random type (examples:strain, stress) which is either directly observed or indirectly estimated from observations by an adjustment procedure. Under the assumption of normalityof tensor components we compute the joint probability density functionas well as the marginal probability density functionsof its eigenspectra (eigenvalues) and eigendirections (orientation parameters). Due to the nonlinearity of the relation between eigenspectra-eigendirections and the random tensor components, via the inverse nonlinear error propagationbiases and aliases of their first and centralized second moments (mean value, variance-covariance) are expressed in terms of Jacobianand Hessianmatrices. The joint probability density function and the first and second moments thus form the fundamental of hypothesis testing and qualify control of eigenspectra (eigenvalues, principal components) and eigendirections (orientation parameters, eigenvectors, principial direction) of a twodimensional, symmetric rank two random tensor. 相似文献
5.
测量数据服从正态分布情况下,最小二乘估计具有最优统计性质,如果测量数据受到粗差干扰而偏离正态分布,就会使最小二乘估计的最优性受到严重冲击,而且估计失实。然而,若采用一次范数最小估计,则所得结果比较好。介绍一次范数最小估计(L1估计)的两种算法——选权迭代法和线性规划法,并通过Matlab模拟实验比较这两种方法的优缺点,证明L1估计的良好抗差性。 相似文献
6.
Georges Blaha 《Journal of Geodesy》1980,54(1):119-135
Second-order derivatives of a general scalar function of position (F) with respect to the length elements along a family of local Cartesian axes are developed in the spheroidal and spherical
coordinate systems. A link between the two kinds of formulations is established when the results in spherical coordinates
are confirmed also indirectly, through a transformation from spheroidal coordinates. IfF becomesW (earth's potential) the six distinct second-order derivatives—which include one vertical and two horizontal gradients of
gravity—relate the symmetric Marussi tensor to the curvature parameters of the field.
The general formulas for the second-order derivatives ofF are specialized to yield the second-order derivatives ofU (standard potential) and ofT (disturbing potential), which allows the latter to be modeled by a suitable set of parameters. The second-order derivatives
ofT in which the property ΔT=0 is explicitly incorporated are also given. According to the required precision, the spherical approximation may or may not
be desirable; both kinds of results are presented. The derived formulas can be used for modeling of the second-order derivatives
ofW orT at the ground level as well as at higher altitudes. They can be further applied in a rotating or a nonrotating field. The
development in this paper is based on the tensor approach to theoretical geodesy, introduced by Marussi [1951] and further
elaborated by Hotine [1969], which can lead to significantly shorter demonstrations when compared to conventional approaches. 相似文献
7.
The cause of the formal difference ofp-norm distribution density functions is analyzed, two problems in the deduction ofp-norm formulating are improved, and it is proved that two different forms ofp-norm distribution density functions are equivalent. This work is useful for popularization and application of thep-norm theory to surveying and mapping. 相似文献
8.
Z. Wiśniewski 《Journal of Geodesy》2009,83(2):105-120
The paper presents a method of estimating parameters in two competitive functional models. The models considered here are
concerned with the same observation set and are based on the assumption that an observation may result from a realization
of either of two different random variables. These variables differ from one another at least in the main characteristic (for
example, outliers can be realizations of one variable). A quantity that describes the opportunity of identifying a single
observation with one random variable is assumed to be known. That quantity, called the elementary split potential, is strictly
referred to the amount of information that an observation can provide about two competitive assumptions concerning the observation
distribution. Parameter assessments that maximize the global elementary split potential (concerning all observations), are
called M
split estimators. A generalization of M
split estimation presented in the paper refers to the theoretical foundation of M-estimation.
An erratum to this article can be found at 相似文献
9.
The observations of theIRIS network are used to study the stability of the determination ofERP fromVLBI. It is concluded that the uncertainties in the initial values ofERP, the errors of other parameters and analyst noise are at the same level as the formal errors in the determination ofERP. The geometric effect on the determination ofERP is important and gives rise to systematic errors. The geometric effect on polar motion is greate than onUT1, and much greater for the continental network. The stability of the determination ofERP fromVLBI can be improved either by creating new stations at reasonable locations in a network or by creating new networks.
At last a comparison is provided between the determinations ofERP from theIRIS andTEMPO networks. 相似文献
10.
LIU Zhengcai ZHU Jianjun WANG Huaiyu 《地球空间信息科学学报》2006,9(3):171-174,186
IntroductionEarlyin 1965 ,a researcher fromFormer SovietUnion put forwardp-norm distribution densityfunction of one variable[1].In 1980 ,an Ameri-can researcher also gave an analogous conclu-sion[2]. In 1993 , a Chinese researcher , SunHaiyan also deduced… 相似文献
11.
在已有的极化合成孔径雷达(PolSAR)图像恒虚警(CFAR)检测方法中,存在着高分辨下杂波模型适用性差的难题。为解决此问题,提出了一种G_0分布下虚警概率具有闭合解析表达形式的CFAR检测方法,并定义虚警损失率(CFAR Loss, C_L)参数用以量化评估CFAR检测方法的恒虚警保持效果。首先,在乘积模型框架下,引入了逆Gamma纹理变量假设,推导出了多视极化白化滤波(MPWF)检测量的概率密度函数(PDF)。然后,对MPWF检测量的概率密度函数积分得到了虚警概率关于CFAR检测阈值的解析表达式,并设计了相应的CFAR检测流程。最后,采用仿真数据和AIRSAR实测数据对已有方法和新方法进行了算法运行时间、检测量拟合性能及目标检测性能对比。实验结果表明,方法运行时间比已有方法缩短3至30倍,具有良好的实时性;日本玉野地区的AIRSAR实测数据结果表明G_0分布对高分辨不均匀海区具有良好的拟合性能,且新方法在G_0分布和非G_0分布海区均能有效检测出目标,鲁棒性较强,相比其他检测方法品质因数(FoM)平均高出15.78%;C_L分析结果表明新方法具有良好的恒虚警保持性能,同时指出杂波对数累积量散点距离G_0分布曲线越近,新方法的恒虚警保持效果越好。 相似文献
12.
DifferentialGPS land kinematic positioning tests conducted at velocities of20 to100 km/h over a baseline of1,000 km using a combination of pseudo-range and phase measurements are described. An algorithm designed for high reliability and
accuracy of1 to2 m in real time field operational mode was utilized. The relatively long baseline used for the tests provided valuable information
on the effects of broadcast ephemeris errors on the differential results. The tests were conducted with two Texas InstrumentsTI4100 receivers using both theP andC/A codes to assess the effect of both code measurement noise, and ionospheric irregularities on differential positioning over
such a baseline. The use of cesium clocks to constrain time was also tested. Accuracies (in terms of repeatabilities) of the
order of1 to3 ppm, i.e.,1 to3 m, were obtained. 相似文献
13.
A unified scheme for processing GPS dual-band phase observations 总被引：3，自引：4，他引：3
A unified computational scheme is presented for sequential least-squares processing ofGPS dual-band carrier-beat-phase observations in network-mode positioning with orbit relaxation, and in orbit determination applications.
This scheme is applicable to any spatial and temporal distribution of stations and satellites during a particularGPS experiment. Full covariance matrices can be specified for carrier-beat-phases and for weighted constraints on the ionosphere
in order to improve phase ambiguity resolution. Physically meaningful choices for these covariance matrices are developed. 相似文献
14.
Sign-constrained robust least squares, subjective breakdown point and the effect of weights of observations on robustness 总被引：3，自引：1，他引：3
Peiliang Xu 《Journal of Geodesy》2005,79(1-3):146-159
The findings of this paper are summarized as follows: (1) We propose a sign-constrained robust estimation method, which can
tolerate 50% of data contamination and meanwhile achieve high, least-squares-comparable efficiency. Since the objective function
is identical with least squares, the method may also be called sign-constrained robust least squares. An iterative version
of the method has been implemented and shown to be capable of resisting against more than 50% of contamination. As a by-product,
a robust estimate of scale parameter can also be obtained. Unlike the least median of squares method and repeated medians,
which use a least possible number of data to derive the solution, the sign-constrained robust least squares method attempts
to employ a maximum possible number of good data to derive the robust solution, and thus will not be affected by partial near
multi-collinearity among part of the data or if some of the data are clustered together; (2) although M-estimates have been
reported to have a breakdown point of 1/(t+1), we have shown that the weights of observations can readily deteriorate such results and bring the breakdown point of
M-estimates of Huber’s type to zero. The same zero breakdown point of the L
1-norm method is also derived, again due to the weights of observations; (3) by assuming a prior distribution for the signs
of outliers, we have developed the concept of subjective breakdown point, which may be thought of as an extension of stochastic
breakdown by Donoho and Huber but can be important in explaining real-life problems in Earth Sciences and image reconstruction;
and finally, (4) We have shown that the least median of squares method can still break down with a single outlier, even if
no highly concentrated good data nor highly concentrated outliers exist.
An erratum to this article is available at . 相似文献
15.
Differential tracking of theGPS satellites in high-earth orbit provides a powerful relative positioning capability, even when a relatively small continental
U.S. fiducial tracking network is used with less than one-third of the fullGPS constellation. To demonstrate this capability, we have determined baselines of up to2000 km in North America by estimating high-accuracyGPS orbits and ground receiver positions simultaneously. The2000 km baselines agree with very long baseline interferometry(VLBI) solutions at the level of1.5 parts in10
8 and showrms daily repeatability of0.3–2 parts in10
8. The orbits determined for the most thoroughly trackedGPS satellites are accurate to better than1 m. GPS orbit accuracy was assessed from orbit predictions, comparisons with independent data sets, and the accuracy of the continental
baselines determined along with the orbits. The bestGPS orbit strategies included data arcs of at least one week, process noise models for tropospheric fluctuations, estimation
ofGPS solar pressure coefficients, and combined processing ofGPS carrier phase and pseudorange data. For data arcs of two weeks, constrained process noise models forGPS dynamic parameters significantly improved the solutions. 相似文献
16.
Analysis on the global morphology of stratospheric gravity wave activity deduced from the COSMIC GPS occultation profiles 总被引：5，自引：0，他引：5
Monthly mean global morphologies of potential energy density E
p
from stratospheric gravity waves are revealed by observations of COSMIC GPS radio occultation. The E
p
is obtained from vertical wavelengths ranging from 2 to 10 km over cells of 1° × 2° in latitude and longitude. The computed
values confirm previous results and obtain new ones. The large gravity wave E
p
values found in the tropics between 25°N and 25°S could be mainly due to the strong tropical cumulus convection; July values
are larger than those for January (2007). In mid and high latitudes, the most prominent features of the northern winter hemisphere
are the enhanced densities above the Eurasian continent and the North Atlantic and the depressed E
p
values above the North Pacific and North America for which topography, wind sources and wind filtering may be responsible.
In southern winter hemisphere, large E
p
values are found around 180° and 300° longitudes that are likely due to the topography of the Antarctic plateau, the Antarctic
Peninsula and South America. Enhanced E
p
values are found over Scandinavia. However, there is no clear evidence to show that gravity waves are localized over the
Rocky Mountains, the Himalayas and the Andes. Topography and planetary wave modulations are proposed to interpret the large-scale
longitudinal variations and inter-hemisphere asymmetry of the GW activity. 相似文献
17.
The positional error in spatial data is defined as a vector by comparing the coordinates between the true position and the measured position. The standard tests to assess the positional accuracy use only the magnitude of the vector and omit the azimuth. This article suggests that the use of both values allows a much more complete analysis of the positional error. A set of tests is proposed that are relevant for this purpose and demonstrate that some important features are not identified by the common procedures. The test samples come from two datasets. The first is obtained from the comparison of 100 homologous points in two conventional maps, and the second one comes from the geometric calibration of a photogrammetric scanner. The results are analyzed and discussed, showing that important issues such as error anisotropy are detected only by means of the circular statistics tests and density maps of distribution. Therefore, tests that assess the goodness of fit for uniform distribution in azimuths, such as Rayleigh and Rao tests, give low probabilities (P = 0 and P > 0.01). Moreover, density maps working with both magnitude and angle can locate the outlier candidate and offer more information about the spatial distribution of error. 相似文献
18.
First and second moments of non-linear least-squares estimators 总被引：1，自引：1，他引：1
Peter J. G. Teunissen 《Journal of Geodesy》1989,63(3):253-262
The first two moments of non-linear and least-squares estimators are studied. Approximate expressions for the moments are
derived and discussed. The results are compared with those ofJeudy [1988]. 相似文献
19.
Richard A. Snay 《Journal of Geodesy》1986,60(1):37-50
Strategies applicable to the design ofGPS surveys involving deployment of either three or four compatible receivers are presented. During aGPS observing session, the receivers operate simultaneously, producing three-dimensional cartesian coordinate differences for
the lines interconnecting the receivers. Different strategies provide the network designer with several options for planning
the survey. The designer may opt for a survey in which each mark is occupied three times, that is, during three separate observing
sessions, or he may elect a more economical survey in which each mark is occupied only twice. The designer may also choose
between two fundamentally different network geometries (a loop geometry or an areal geometry) to design a survey compatible
with the spatial distribution of network marks. The strategies can be extended to other geometries. The strategies produce
efficient networks in that no two marks are jointly occupied for more than one observing session. This feature produces the
maximum number of distinct, directly observed lines for the given number of receivers and observing sessions. The strategies
also favor observations over those lines connecting marks near one another. This feature helps survey logistics by reducing
travel time between observing sessions. 相似文献
20.
Traditionally Inertial Surveying Systems (ISS) are used for missions of30 km to 100 km length. Today, a new type ofISS application is emanating from an increased need for survey control densification in urban areas often in connection with
land information systems or cadastral surveys.
The accuracy requirements of urban surveys are usually high. The loss in accuracy caused by the coordinate transfer betweenIMU and ground marks is investigated and an offsetting system based on electronic tacheometers is proposed.
An offsetting system based on a Hewlett-PackardHP 3820A electronic tacheometer has been tested in Sydney (Australia) in connection with a vehicle mountedLITTON Auto-Surveyor SystemII. On missions over750 m (8 stations,25 minutes duration,3.5 minuteZUPT intervals, mean offset distances 9 metres) accuracies of37 mm (one sigma) in position and8 mm in elevation were achieved. Some improvements to theLITTON Auto-Surveyor SystemII are suggested which would improve the accuracies even further. 相似文献