共查询到20条相似文献,搜索用时 375 毫秒
1.
M. E. O’Kelly 《Journal of Geographical Systems》2009,11(3):227-241
The minimax hub location problem sites a facility to minimize the maximum weighted interaction cost between pairs of fixed nodes. In this paper, distances are represented by a rectilinear norm and may be suited to factory layout or street
network problems. The problem is already well known (in 2-D) as the round trip location problem and is extended to 3-D in
this paper. One rationale for the solution method is based on an extension of the geometric arguments used to solve the minimax
single facility location problem. Suppose a budget is provided for interactions, and that each interaction must be accomplished
for no more than this cost. The algorithm uses a bi-section search for the feasible budget until it finds the expenditure
needed to provide for these flows. The extension in the present paper is that the nodes are permitted to be on different layers
(levels). This 3-D version of the problem appears to be a new variant of the hub model. The models and solution techniques
developed in the paper are illustrated using a small 55 node problem. Because of a relatively efficient implementation of
the bi-section search, the algorithm in 2-D and 3-D is also applied successfully to a 550 node problem.
相似文献
M. E. O’KellyEmail: |
2.
Siting service facilities in order to maximize regional coverage is important when budget resources are limited. Various approaches exist for addressing this particular planning problem for discrete or continuous representations of potential facility sites and demand to be served. In cases where both candidate facility sites and service demand are continuous, approaches for maximizing regional coverage have only examined the siting of a single facility. In this article, a geocomputational approach is proposed for addressing multiple facility siting when demand is continuously distributed and facilities may be located anywhere in the region. Emergency warning siren location is used to highlight the developed approach. 相似文献
3.
Show me the code: spatial analysis and open source 总被引:3,自引:1,他引:2
Sergio J. Rey 《Journal of Geographical Systems》2009,11(2):191-207
This paper considers the intersection of academic spatial analysis with the open source revolution. Its basic premise is that
the potential for cross-fertilization between the two is rich, yet some misperceptions about these two communities pose challenges
to realizing these opportunities. The paper provides a primer on the open source movement for academicians with an eye towards
correcting these misperceptions. It identifies a number of ways in which increased adoption of open source practices in spatial
analysis can enhance the development of the next generation of tools and the wider practice of scientific research and education.
相似文献
Sergio J. ReyEmail: |
4.
A constrained LAMBDA method for GPS attitude determination 总被引:4,自引:0,他引:4
An improved method to obtain fixed integer ambiguity in GPS attitude determination is presented. Known conditions are utilized
as constraints to acquire attitude information when the float solution and its variance–covariance matrix are not accurate
enough. The searching ellipsoidal region is first expanded to compensate for errors caused by the inaccurate float solution.
Then the constraints are used to shrink the region to a proper size, which maintains the true integer ambiguity. Experimental
results demonstrate that this scheme gives a fast search time and a higher success rate in determining the fixed integer ambiguity
than the unconstrained method. The accuracy of attitude angles is also improved.
相似文献
Bo WangEmail: |
5.
In this paper a MATLAB toolbox for determining the attitude of a rigid platform by means of multiple non-dedicated antennas
using global positioning system is presented. The programs embedded in this toolbox cover the RINEX data analysis, single
point positioning, differential positioning, coordinate conversion, attitude determination, and other auxiliary functions.
After forming the baselines through double-differenced (carrier phase smoothed) code observables, the attitude parameters
are obtained by applying the direct attitude computation and the least squares attitude estimation. The theoretical background
is summarized, and some hints regarding the software implementation are given in the paper. Moreover, improvements yielding
an expanded functionality are proposed.
相似文献
Zhen DaiEmail: |
6.
Separate space- or time-lags have been considered regularly in data analyses; as space–time models are more recently being
studied extensively in data analytic fashion, joint estimation of both lags has to be considered explicitly. This paper addresses
this issue, taking into special consideration parametric parsimony together with specification richness; use of the bivariate
Poisson frequency distribution is advocated and applied to an empirical case. The relation of this approach to random effects
specifications is investigated. Data for Belgian regional products constitute the empirical case study.
相似文献
Daniel A. GriffithEmail: |
7.
In this article, an algorithm for clock offset estimation of the GPS satellites is presented. The algorithm is based on a
Kalman-filter and processes undifferenced code and carrier-phase measurements of a global tracking network. The clock offset
and drift of the satellite clocks are estimated along with tracking station clock offsets, tropospheric zenith path delay
and carrier-phase ambiguities. The article provides a brief overview of already existing near-real-time and real-time clock
products. The filter algorithm and data processing scheme is presented. Finally, the accuracy of the orbit and clock product
is assessed with a precise orbit determination of the MetOp satellite and compared to results gained with other real-time
products.
相似文献
André HauschildEmail: |
8.
The architecture of the ultra-tight GPS/INS/PL integration is the key to its successful performance; the main feature of this
architecture is the Doppler feedback to the GPS receiver tracking loops. This Doppler derived from INS, when integrated with
the carrier tracking loops, removes the Doppler due to vehicle dynamics from the GPS/PL signal thereby achieving a significant
reduction in the carrier tracking loop bandwidth. The bandwidth reduction provides several advantages such as: improvement
in anti-jamming performance, and increase in post correlated signal strength which in turn increases the dynamic range and
accuracy of measurements. Therefore, any degradation in the derived Doppler estimates will directly affect the tracking loop
bandwidth and hence its performance. The quadrature signals from the receiver correlator, I (in-phase) and Q (quadrature),
form the measurements, whereas the inertial sensor errors, position, velocity and attitude errors form the states of the complementary
Kalman filter. To specify a reliable measurement model of the filter for this type of integrated system, a good understanding
of GPS/PL signal characteristics is essential. It is shown in this paper that phase and frequency errors are the variables
that relate the measurements and the states in the Kalman filter. The main focus of this paper is to establish the fundamental
mathematical relationships that form the measurement model, and to show explicitly how the system error states are related
to the GPS/PL signals. The derived mathematical relationships encapsulated in a Kalman filter, are tested by simulation and
shown to be valid.
相似文献
Ravindra Babu (Corresponding author)Email: |
Jinling WangEmail: |
9.
Lambert Wanninger 《GPS Solutions》2009,13(2):133-139
Antenna changes at GNSS reference stations frequently produce discontinuities in the coordinate time series. These apparent
position shifts are mainly caused by changes of carrier-phase multipath effects and different errors in the antenna phase
center corrections. A monitoring method was developed and successfully tested, which requires additional GNSS observations
from a local, temporary reference station. Changes of carrier-phase measurement errors due to the antenna change are determined
and stored in L1 and L2 phase maps. These phase maps provide corrections to be applied either to the observation data obtained
before the antenna change or to the observation data obtained after the antenna change. The observation corrections are able
to remove coordinate discontinuities independent of the selected coordinate estimation algorithm.
相似文献
Lambert WanningerEmail: |
10.
Since the assumption of all stations tracking the same satellites with identical weights was previously employed by Shen and
Xu (GPS Solut 12:99–108, 2008) to derive the simplified GNSS single- and double-differenced equivalent equations, this supplementary paper expands these
simplified equations in the case of each station tracking different satellites with elevation-dependent weights. Numerical
experiments are performed to demonstrate the computational efficiency of the simplified equivalent algorithm relative to the
traditional method in various scenarios of multi-baseline solutions with tracking different satellites. The fast computational
speed of the simplified equivalent algorithm will potentially benefit the local, regional and even global GNSS multi-baseline
solutions as well as the combined GNSS application.
相似文献
Guochang XuEmail: |
11.
Identifying barriers of species and characterize their effects on spatial distribution provide essential information to research
in landscape genetics. We propose a weighted difference barrier (WDB) method as an alternative to maximum difference barriers
(MDB), and to initiate and integrate more spatial modeling and methods into the problem solving process. Overall, WDB provides
quick and straightforward improvements to the drawbacks of MDB. WDB integrates more sample location relationships into the
barrier construction and reveals potential barriers that would otherwise go undetected. WDB incorporates both within group
and between group genetic information, and delineates the barriers as a more complex pattern.
相似文献
John RadkeEmail: |
12.
Digital mobile mapping, the method that integrates digital imaging with direct geo-referencing, has developed rapidly over
the past 15 years. The Kalman filter (KF) is considered an optimal estimation tool for real-time INS/GPS integrated kinematic
positioning and orientation determination. However, the accuracy requirements of general mobile mapping applications cannot
be easily achieved even when using the KF scheme. Therefore, this study proposes an intelligent scheme combining ANN and RTS
backward smoother to overcome the limitations of KF and to enhance the overall accuracy of attitude determination for tactical
grade and MEMS INS/GPS integrated systems.
相似文献
Yun-Wen Huang (Corresponding author)Email: |
13.
A sampling approach to estimate the log determinant used in spatial likelihood problems 总被引:2,自引:1,他引:1
Likelihood-based methods for modeling multivariate Gaussian spatial data have desirable statistical characteristics, but the
practicality of these methods for massive georeferenced data sets is often questioned. A sampling algorithm is proposed that
exploits a relationship involving log-pivots arising from matrix decompositions used to compute the log determinant term that
appears in the model likelihood. We demonstrate that the method can be used to successfully estimate log-determinants for
large numbers of observations. Specifically, we produce an log-determinant estimate for a 3,954,400 by 3,954,400 matrix in
less than two minutes on a desktop computer. The proposed method involves computations that are independent, making it amenable
to out-of-core computation as well as to coarse-grained parallel or distributed processing. The proposed technique yields
an estimated log-determinant and associated confidence interval.
相似文献
James P. LeSage (Corresponding author)Email: |
14.
Ionospheric delay corrections for single-frequency GPS receivers over Europe using tomographic mapping 总被引:3,自引:2,他引:1
The majority of navigation satellites receivers operate on a single frequency and experience a positioning error due to the
ionospheric delay. This can be compensated for using a variety of approaches that are compared in this paper. The study focuses
on the last solar maximum. A 4D tomographic imaging technique is used to map the ionospheric electron density over the European
region during 2002 and 2003. The electron density maps are then used to calculate the excess propagation delay on the L1 frequency
experienced by GPS receivers at selected locations across Europe. The excess delay is applied to correct the pseudo-range
single frequency observations at each location and the improvements to the resulting positioning are calculated. The real-time
tomographic technique is shown to give navigation solutions that are better than empirical modelling methods and approach
the accuracy of the full dual-frequency solution. The improvements in positioning accuracy vary from day to day depending
on ionospheric conditions but can be up to 25 m during mid-day during these solar maximum conditions at European mid-latitudes.
相似文献
Damien J. AllainEmail: |
15.
A data archive of GPS navigation messages 总被引:2,自引:1,他引:1
Since 18 June 2007 navigation data messages transmitted by the GPS constellation are recorded by five receivers within GeoForschungsZentrum’s
global groundstation network. We describe the recording, processing, validation, analysis and archiving of the navigation
data. During the 197 days between 18 June 2007 and 31 December 2007 a total of 125,723,666 subframes were collected. By taking
into consideration that the same data set frequently is observed by two or more receivers concurrently, 65,153,955 unique
subframes could be extracted from the observations. With an estimated 88,099,200 subframes transmitted by the constellation
during this time period a data yield of about 74% was achieved. Simulation studies suggest that with two additional GPS receivers,
which are scheduled for addition to the network in 2008, about 95% of the transmitted subframes will be retrieved. The message
data archive is open to the scientific community for non-commercial purposes and may be accessed through GFZ’s Information
System and Data Center ().
相似文献
G. BeyerleEmail: |
16.
Modeling spatial autocorrelation in spatial interaction data: empirical evidence from 2002 Germany journey-to-work flows 总被引:3,自引:3,他引:0
Daniel A. Griffith 《Journal of Geographical Systems》2009,11(2):117-140
Since before the inception of work by Okabe, the intermingling of spatial autocorrelation (i.e., local distance and configuration)
and distance decay (i.e., global distance) effects has been suspected in spatial interaction data. This convolution was first
treated conceptually because technology and methodology did not exist at the time to easily or fully address spatial autocorrelation
effects within spatial interaction model specifications. Today, however, sufficient computer power coupled with eigenfunction-based
spatial filtering offers a means for accommodating spatial autocorrelation effects within a spatial interaction model for
modest-sized problems. In keeping with Okabe’s more recent efforts to dissemination spatial analysis tools, this paper summarizes
how to implement the methodology utilized to analyze a particular empirical flows dataset.
相似文献
Daniel A. GriffithEmail: |
17.
This study adopts the Chiu-fen-erh-shan landslide as a case study for incorporating comprehensive accelerograph and global
positioning system (GPS) data to determine the best-fit acceleration data for analyzing a rock avalanche. Previous investigations
indicate that the distance from an accelerograph to a landslide site is crucial to determining the best-fit acceleration data
to use in conducting a seismic analysis. Unfortunately, the Chiu-fen-erh-shan landslide and its nearest accelerograph station
are located in different geological zones. Thus, GPS data were compared to the displacements derived from the accelerograms
of nearby monitoring stations to help select the best accelerograph data. This emphasizes that a high density distribution
of accelerographs and GPS installations are essential to acquire the best data for the seismic analysis, especially in complex
geological zones. After applying the best-fit accelerogram to Newmark’s sliding model and an empirical displacement attenuation
formula to back-calculate the shear strength parameters of the sliding surface, a cohesion of 0 kPa and friction angle of
the sliding surface of 24.8° were found for this landslide.
相似文献
Jian-Hong WuEmail: Email: |
18.
Troposphere zenith path delays derived from the Global Data Assimilation System (GDAS) numerical weather model (NWM) are compared
with those of the International GNSS Service (IGS) solutions over a 1.5-year period at 18 globally distributed IGS stations.
Meteorological parameters can be interpolated from the NWM model at any location and at any time after December 2004. The
meteorological parameters extracted from the NWM model agree with in situ direct measurements at some IGS stations within
1 mbar for pressure, 3° for temperature and 13% for relative humidity. The hydrostatic and wet components of the zenith path
delay (ZPD) are computed using the meteorological parameters extracted from the NWM model. The total ZPDs derived from the
GDAS NWM agree with the IGS ZPD solutions at 3.0 cm RMS level with biases of up to 4.5 cm, which can be attributed to the
wet ZPDs estimates from the NWM model, considering the less accurate interpolated relative humidity parameter. Based on this
study, it is suggested that the availability and the precision of the GDAS NWM ZPD should be sufficient for nearly all GPS
navigation solutions.
相似文献
Constantin-Octavian AndreiEmail: |
19.
Pitch and roll attitude estimation of a small-scaled helicopter using single antenna GPS with gyroscopes 总被引:2,自引:2,他引:0
A method is presented for estimating the roll and pitch attitude of a small-scaled unmanned helicopter based on the velocity
measurements of the global positioning system (GPS). The small-scaled helicopter is a radio controlled (RC) model which is
readily available and affordable for academic laboratories as a research platform. Only one single antenna GPS receiver is
equipped on the RC helicopter to acquire the velocity measurements needed for the attitude estimation. The velocity information
is recorded by the onboard computer for post-processing. An attitude and heading reference system (AHRS) is used to provide
the reference attitudes. The required angular rates and heading for this study are also given by the gyroscopes and compass
of the AHRS for the sake of system’s simplification. The Kalman filter is applied to estimate the helicopter’s accelerations
by using the GPS velocity measurements. The estimated accelerations form the fundamental elements of synthesizing the pseudo-roll
and the pseudo-pitch. With some legitimate simplifications and assumptions, the relation between the helicopter’s attitudes
and the accelerations estimated from the GPS velocity measurements can be developed. Furthermore, to enhance the accuracy
of the pseudo-attitudes, the angular rates acquired from the gyroscopes are incorporated into the estimation algorithm of
pseudo-attitudes by using a complementary filter.
相似文献
Fei-Bin HsiaoEmail: |
20.
Incorporating spatial variation in housing attribute prices: a comparison of geographically weighted regression and the spatial expansion method 总被引:10,自引:3,他引:7
Christopher Bitter Gordon F. Mulligan Sandy Dall’erba 《Journal of Geographical Systems》2007,9(1):7-27
Hedonic house price models typically impose a constant price structure on housing characteristics throughout an entire market
area. However, there is increasing evidence that the marginal prices of many important attributes vary over space, especially
within large markets. In this paper, we compare two approaches to examine spatial heterogeneity in housing attribute prices
within the Tucson, Arizona housing market: the spatial expansion method and geographically weighted regression (GWR). Our
results provide strong evidence that the marginal price of key housing characteristics varies over space. GWR outperforms
the spatial expansion method in terms of explanatory power and predictive accuracy.
相似文献
Christopher BitterEmail: |