Analyzing Cognitive Conceptualizations Using Interactive Visual Environments

The conceptualization of spatio-temporal information is an interdisciplinary research area. The focus of this article is on human conceptualizations of spatio-temporal geographic phenomena (also referred to as events). Identifying and understanding human conceptualizations is a crucial component in defining the semantics of spatio-temporal information. However, most research focuses primarily on how humans imbue dynamic phenomena with meaning on a general level. In contrast, this article is concerned with contextual factors (specifically: individual differences) that are too often neglected in general theories and in the analysis of behavioral data. In other words, we are interested in individual or group strategies of participants that are not detected by classical analysis methods. Research on individual difference is gaining widespread attention in cognitive and spatial sciences and it is time to consider individual differences in the area of conceptualizing spatio-temporal information. To understand individual differences in behavioral data on how people conceptualize events, we have developed illustrative software and have combined them with established similarity measures. We demonstrate the feasibility of our approach, its usefulness in analyzing behavioral data, and results that can be obtained through this individualized analysis by reanalyzing four sets of experimental data we previously collected.     

基于经验模态分解的GPS基线解算模型

非建模系统误差是影响高精度GPS基线解算精度的一个重要因素,文章给出基于经验模态分解的GPS基线解算模型,有效消弱系统误差对基线解的影响。在现有经验模态分解理论的基础上,定义经验模态分解的多尺度分解与重构结构,并由此给出基于经验模态的系统趋势分离模型,依据累积标准化模量的均值随尺度的变化确定系统误差与噪声分离尺度的选择标准。给出基于经验模态分解的GPS基线解算的技术路线,首先计算GPS相位双差观测方程的浮点解残差序列,分离出系统误差并用于修正GPS双差观测值,重新计算双差浮点解,采用Lambda算法固定整周模糊度,计算固定基线解,从而消弱系统误差对基线解算的影响,提高基线固定解的可靠性。并采用实测GPS数据验证模型,F-ratio指数与W-ratio指数表明系统误差消弱后,基线固定解可靠性得到明显提高,重新计算的残差序列表明系统误差得到很好的消弱。     

GPS连续运行参考站网络的解的精度及其稳定性研究

利用澳大利亚的维多利亚GPS连续运行参考站网络的原始观测数据、GPS精密数据处理软件和统计分析方法,对GPS网络的解的精度(CORS)及其稳定性与所用的数据量之间的关系进行了深入研究。结果表明：(1)解的精度与数据量之间存在密切的相关关系,其关系可以用非线性回归方程来表示;(2)数据量从1h增加到6h,解的精度随着数据量的增加而迅速提高,而在数据量大于6h以后,提高的速率较为缓慢;(3)对于平均基线长度为数百km、最长的基线边超过1000km的GPS连续运行参考站网络,其在6h以内的解的精度和稳定性不高,不宜用于高精度的测量与定位服务,当数据量达到12h以后,解算结果及其精度趋于稳定,24h解(单日解)具有很高的稳定性,其坐标精度优于5mm;(4)GPS网络的解随着数据量的增加而收敛于单日解。     

Gross Error Compensation for Gravity Field Analysis Based on Kinematic Orbit Data

This paper aims at a comparative study of several measures to compensate for gross errors in kinematic orbit data. It starts with a simulation study on the influence of a single outlier in the orbit data on the gravity field solution. It is shown that even a single outlier can degrade the resulting gravity field solution considerably. To compensate for outliers, two different strategies are investigated: wavelet filters, which detect and eliminate gross errors, and robust estimators, which due to an iterative downweighting gradually ignore those observations that lead to large residuals. Both methods are applied in the scope of the analysis of a 2-year kinematic CHAMP (challenging minisatellite payload) orbit data set. In various real data studies, robust estimators outperform wavelet filters in terms of resolution of the derived gravity field solution. This superior performance is at the cost of computational load, as robust estimators are implemented iteratively and require the solution of large sets of linear equations several times.     

THEORETICAL MODELS OF THE ACCURACY OF DIGITAL TERRAIN MODELS: AN EVALUATION AND SOME OBSERVATIONS

This paper is an attempt to evaluate existing theoretical models for the accuracy of digital terrain models (DTM) both through a theoretical analysis and by experimental tests. In order to extend the discussion, some comments on the general form in which a DTM accuracy model should be constructed are also made and a possible solution is offered.     

Analytical dynamic orbit improvement for the evaluation of geodetic-geodynamic satellite data

Summary Given an analytical solution (solution of the equations of motion using analytical integration techniques) an integration of the variational equations is not necessary but simply a differentiation of the analytical solution. Based on a high-precision analytical solution explicit expressions for the coefficients of the observation equations to improve state variables and force model parameters have been derived.The definition of suitable unknowns for a pure dynamic orbital improvement can be based then on an analysis of the information content of the data at hand by using those expressions.Regarding the Fourier series structure of orbital perturbations as well as the special properties of crossover difference data, the proposed technique is particularly favourable for an evaluation of Remote Sensing Data such as altimeter, SST and gradiometer data from satellites in repeating orbits.After a general discussion of the observation equations for crossover data our present results using GEOSAT altimeter data are discussed as one example for applications. Some short remarks about further applications are given.     

树模型的三维可视化研究

树的表达无论是在3DGIS，VRGIS还是在3DCM中，都是一个难点问题。与一般实体对象不同的是，树明显具有分形空间特征，因此用常规简单的建模方法很难表达一颗树。现在分形算法常用来生成树模型，具有逼真的可视效果，但所产生的数据量对于GIS环境来说太大，可视化困难；另外，用树的图像替代树模型也是一种常用的方法，但在近视点视觉效果差，同时也没有表达出树木所固有的空间特征。本文作者提出一种方法，使用LOD技术，将树的分形模型与其图像替代模型两者结合起来，初步解决树模型在GIS中的可视化问题，可达到逼真、高速的可视效果。     

利用残差统计检验评估区域GPS大地测量网解算方案

采用美国喷气推进实验室JPL发展的GIPSY软件解算区域GPS网，比较了固家精密星历和同时固定精密星历及卫星钟参数2种解算方案，残差统计检验表明前者的左中仍保留了部分未解出的信号而后者的残差接近于白噪声高斯分布，解算结果与ITRF96的比较和对重复率的统计表明，残差分布合理的解算较优，简单的线差统计检验的计算可提供重要的解算评估。     

一种附加边界约束和内约束的多中心ERP融合模型

不同技术、不同分析中心得到的地球自转参数（Earth rotation parameters,ERP）往往是不同的,为提供统一的ERP供用户使用,常需对ERP进行融合处理。提出了一种基于多分析中心ERP结果的附加边界约束和内约束融合模型,即先通过参数变换把各分析中心结果转换到相同时刻,考虑到相邻观测时段边界点处ERP应当一致这一特点,施加边界约束,然后对各分析中心的长期解施加转换参数内约束,最后得到多分析中心ERP的融合解。采用从2005—2011年共6 a的7个全球卫星导航系统（Global Navigation Satellite System,GNSS）分析中心的结果进行融合处理,并与IERS C04（International Earth Rotation and Reference Systems ServiceCombined 04）结果进行比较。结果表明,所提出的融合方法计算结果的精度有明显改善。     

GPS Solutions: Closed Forms, Critical and Special Configurations of P4P

P4P is the pseudo-ranging 4-point problem as it appears as the basic configuration of satellite positioning with pseudo-ranges as observables. In order to determine the ground receiver/satellite receiver (LEO networks) position from four positions of satellite transmitters given, a system of four nonlinear (algebraic) equations has to be solved. The solution point is the intersection of four spherical cones if the ground receiver/satellite receiver clock bias is implemented as an unknown. Here we determine the critical configuration manifold (Determinantal Loci, Inverse Function Theorem, Jacobi map) where no solution of P4P exists. Four examples demonstrate the critical linear manifold. The algorithm GS solves in a closed form P4P in a manner similar to Groebner bases: The algebraic nonlinear observational equations are reduced in the forward step to one quadratic equation in the clock bias unknown. In the backward step two solutions of the position unknowns are generated in closed form. Prior information in P4P has to be implemented in order to decide which solution is acceptable. Finally, the main target of our contribution is formulated: Can we identify a special configuration of satellite transmitters and ground receiver/satellite receiver where the two solutions are reduced to one. A special geometric analysis of the discriminant solves this problem. ? 2002 Wiley Periodicals, Inc.     

联合高低卫-卫跟踪和卫星重力梯度数据恢复地球重力场的谱组合法

GOCE采用的高低卫-卫跟踪和卫星重力梯度测量技术在恢复重力场方面各有所长并互为补充,如何有效利用这两类观测数据最优确定地球重力场是GOCE重力场反演的关键问题。本文研究了联合高低卫-卫跟踪和卫星重力梯度数据恢复地球重力场的最小二乘谱组合法,基于球谐分析方法推导并建立了卫星轨道面扰动位T和径向重力梯度Tzz、以及扰动位T和重力梯度分量组合{Tzz-Txx-Tyy}的谱组合计算模型与误差估计公式。数值模拟结果表明,谱组合计算模型可以有效顾及各类数据的精度和频谱特性进行最优联合求解。采用61天GOCE实测数据反演的两个180阶次地球重力场模型WHU_GOCE_SC01S（扰动位和径向重力梯度数据求解）和WHU_GOCE_SC02S（扰动位和重力梯度分量组合数据求解）,结果显示后者精度优于前者,并且它们的整体精度优于GOCE时域解,而与GOCE空域解的精度接近,验证了谱组合法的可行性与有效性。     

Impact of sampling rate of IGS satellite clock on precise point positioning

Both static and kinematic testings are investigated by using IGS 5min, 30s and 5s-interval precise satellite clock products in precise point positioning (PPP) solution. Test results show that the sampling rate of IGS satellite clock has very little effect on the static PPP solution. All the three types of sampling intervals of precise satellite clock can satisfy mm-cm level of positioning accuracy; higher sampling rate has no significant improvement for PPP solution. However, sampling rate of satellite clock has a significant impact on the PPP solution in kinematic PPP. The higher the interval of satellite clock, the better the accuracy achieved. The accuracy of kinematic PPP achieved by using 30s-interval precise satellite clock is improved by nearly 30–50 percent with respect to the solution by using 5min-interval precise satellite clock, but using 5s and 30s-interval satellite clock can almost produce the same accuracy of kinematic solution. Moreover, the use of precise satellite clock products from different analysis centers may also produce more or less effect on the PPP solution.     

Impact of sampling rate of IGS satellite clock on precise point positioning

Both static and kinematic testings are investigated by using IGS 5min, 30s and 5s-interval precise satellite clock products in precise point positioning (PPP) solution. Test results show that the sampling rate of IGS satellite clock has very little effect on the static PPP solution. All the three types of sampling intervals of precise satellite clock can satisfy mm-cm level of positioning accuracy; higher sampling rate has no significant improvement for PPP solution. However, sampling rate of satellite clock has a significant impact on the PPP solution in kinematic PPP. The higher the interval of satellite clock, the better the accuracy achieved. The accuracy of kinematic PPP achieved by using 30s-interval precise satellite clock is improved by nearly 30–50 percent with respect to the solution by using 5min-interval precise satellite clock, but using 5s and 30s-interval satellite clock can almost produce the same accuracy of kinematic solution. Moreover, the use of precise satellite clock products from different analysis centers may also produce more or less effect on the PPP solution.     

利用2006—2015年VLBI数据进行地球定向参数解算与分析

目前正处在下一代甚长基线干涉测量（very long baseline interferometry,VLBI）系统的建设时期。利用维也纳VLBI与卫星软件（Vienna VLBI and satellite software,VieVS）解算了2006—2015年的VLBI数据,得到了10 a的地球定向参数（Earth orientation parameters,EOP）时间序列,并与国际地球自转服务机构的结果进行了对比。利用解算结果得到了10 a的日长变化时间序列,通过傅里叶分析得出了日长变化的短周期、半月周期、月周期、半年周期和周年周期,同时还分析得到了极移序列中的周年项和张德勒周期项以及章动改正序列中的自由核章动项。此次解算工作可为武汉大学卫星台站日后的VLBI数据解析积累一定的经验。     

地球物理反问题中两种正则化方法的比较

通过对最小二乘法的改造引入了两种正则化方法及其解的表达式，从理论上阐述了Tikhonov与TS—VD两种正则化方法效果的差异，特别就病态方程组在三种情况——系数阵良定秩、系数阵劣定秩右端项劣衰减、系数阵劣定秩右端项良衰减下正则化方法的应用效果作了比较．并给出了数值例子。     

伪距单点定位两域联合平差解的等价性分析

针线性观测模型观测值域联合平差解和平差值域联合平差解完全等价,但实际中联合平差的观测模型多为非线性模型,参数估计时常常需要进行线性化处理,存在线性化引起的模型误差,该误差对两域平差解的等价性影响值得探讨.以伪距单点定位(SPP)为例,论文推导了其平差值域联合平差求解公式,分析了两域联合平差不能完全等价的原因,并用实例进行了数值对比.研究表明：在配置相同的情况下,不同全球卫星导航系统(GNSS)组合SPP的两域平差位置解在毫米量级上数值相同,就SPP应用而言,两域平差解可认为相同.论文内容对于一些GNSS其他应用也具有一定的参考意义.     

Apropos laser tracking to GPS satellites

. Laser tracking to GPS satellites (PRN5 and 6) provides an opportunity to compare GPS and laser systems directly and to combine data of both in a single solution. A few examples of this are given in this study. The most important results of the analysis are that (1) daily SLR station coordinate solutions could be generated with a few cm accuracy; (2) coordinates of nine stations were determined in a 2.3-year-long arc solution; (3) the contribution of laser data on the `SLR-GPS' combined orbit, resulting from the simultaneous processing of SLR and GPS data, is significant and (4) laser-only orbits have an accuracy of 10–20 cm, 1-day predictions of SLR orbits differ from IGS orbits by about 20–40 cm, 2-day predictions by 50–60 cm. Received: 1 October 1996 / Accepted: 14 February 1997     

Discovering spatial and temporal patterns from taxi-based Floating Car Data: a case study from Nanjing

Floating Car Data (FCD) refers to the trajectories of vehicles equipped with Global Positioning System-enabled devices that automatically record location-related data within a short time interval. As taxies in Chinese cities continually drive along the streets seeking passengers, FCD can easily traverse the entire street network in a city on a daily basis. Taking advantage of this situation, this study extracted passenger pickup and drop-off locations from FCD sourced from 6445 taxis over a 2-week period in Nanjing, China to discover human behavioral patterns and the dynamics behind them. In this study, road nodes are converted to the points, based on which Thiessen polygons are generated to divide the study area into small areas with the goal of exploring the spatial distribution of pickup and drop-off locations. Moran’s I index is used to calculate the spatial autocorrelation of the spatial distribution of pickup and drop-off locations, and hot spot analysis is used to identify statistically significant spatial clusters of hot and cold spots. The spatial and temporal patterns of FCD in the study area are investigated, and the results show that: (1) the temporal patterns show a strong daily rhythm, (2) the spatial patterns show that the number of pickup and drop-off locations gradually diminish from the downtown areas to the outer suburbs, (3) the spatiotemporal patterns exhibit large differences over time, and (4) the driving forces explored by regression models indicate that population density and transportation density are consistent with the population distribution, but per capita disposable income is not consistent with the population distribution.     

Spatial microsimulation modeling for residential energy demand of England in an uncertain future

High quality infrastructure is crucial to economic success and the sustainability of society. Infrastructures for services, such as transport, energy, and water supply, also have long lead times, and therefore require effective long-term planning. In this paper, we report on work undertaken as part of the UK Infrastructure Transitions Research Consortium to construct long-term models of demographic change which can help to inform infrastructure planning for transport, energy, and water as well as IT and waste. A set of demographic microsimulation models (MSM), which are spatially disaggregate to the geography of UK Local Authorities, provides a high level of detail for understanding the drivers of changing patterns of demand. However, although robust forecasting models are required to support projections based on the notion of ‘predict-and-provide,’ the potential for behavioral adaptation is also an important consideration in this context. In this paper, we therefore establish a framework for linkage of a MSM of household composition, with behavior relating to the consumption of energy. We will investigate variations in household energy consumption within and between different household groups. An appropriate range of household types will be defined through the application of decision trees to consumption data from a detailed survey produced by the UK Department of Energy and Climate Change. From this, analysis conclusions will be drawn about the impact of changing demographics at both household and individual level, and about the potential effect of behavioral adjustments for different household groups.     

A Comparative Analysis of Traveling Salesman Solutions from Geographic Information Systems

The Traveling Salesman Problem is one of the most prominent problems in combinatorial optimization, and is regularly employed in a wide variety of applications. The objective of this article is to demonstrate the extent of sub‐optimality produced by Traveling Salesman solution procedures implemented in the context of Geographic Information Systems and to discuss the consequences that such solutions have for practice. Toward that end, an analysis is made of Traveling Salesman solutions from implementations in four Geographic Information System packages. These implementations are tested against the optimal solution for a range of problem sizes. Computational results are presented in the context of a school bus routing application. This analysis concludes that no Traveling Salesman implementation in GIS is likely to find the optimal solution when problems exceed 10 stops. In contrast, optimal solutions can be generated with desktop linear programming software for up to 25 cities. Moreover, one GIS implementation consistently found solutions that were closer to optimal than its competitors. This research strongly suggests that for applications with fewer than 25 stops, the use of an optimal solution procedure is advised, and that GIS implementations can benefit from the integration of more robust optimization techniques.