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11.
12.
OpenStreetMap (OSM) is one of the most popular examples of a Volunteered Geographic Information (VGI) project. In the past years it has become a serious alternative source for geodata. Since the quality of OSM data can vary strongly, different aspects have been investigated in several scientific studies. In most cases the data is compared with commercial or administrative datasets which, however, are not always accessible due to the lack of availability, contradictory licensing restrictions or high procurement costs. In this investigation a framework containing more than 25 methods and indicators is presented, allowing OSM quality assessments based solely on the data's history. Without the usage of a reference data set, approximate statements on OSM data quality are possible. For this purpose existing methods are taken up, developed further, and integrated into an extensible open source framework. This enables arbitrarily repeatable intrinsic OSM quality analyses for any part of the world. 相似文献
13.
Ben K. H. Soon Steve Scheding Hyung-Kuen Lee Hung-Kyu Lee Hugh Durrant-Whyte 《GPS Solutions》2008,12(4):261-271
This paper presents a simple and effective approach that incorporates single-frequency, L1 time-differenced GPS carrier phase
(TDCP) measurements without the need of ambiguity resolution techniques and the complexity to accommodate the delayed-state
terms. Static trial results are included to illustrate the stochastic characteristics and effectiveness of the TDCP measurements
in controlling position error growth. The formulation of the TDCP observation model is also described in a 17-state tightly-coupled
GPS/INS iterative, extended Kalman filter (IEKF) approach. Preliminary land vehicle trial results are also presented to illustrate
the effectiveness of the TDCP which provides sub-meter positional accuracies when operating for more than 10 min. 相似文献
14.
There is a common belief that the presence of residual spatial autocorrelation in ordinary least squares (OLS) regression
leads to inflated significance levels in beta coefficients and, in particular, inflated levels relative to the more efficient
spatial error model (SEM). However, our simulations show that this is not always the case. Hence, the purpose of this paper
is to examine this question from a geometric viewpoint. The key idea is to characterize the OLS test statistic in terms of
angle cosines and examine the geometric implications of this characterization. Our first result is to show that if the explanatory
variables in the regression exhibit no spatial autocorrelation, then the distribution of test statistics for individual beta
coefficients in OLS is independent of any spatial autocorrelation in the error term. Hence, inferences about betas exhibit all the optimality properties of
the classic uncorrelated error case. However, a second more important series of results show that if spatial autocorrelation
is present in both the dependent and explanatory variables, then the conventional wisdom is correct. In particular, even when
an explanatory variable is statistically independent of the dependent variable, such joint spatial dependencies tend to produce
“spurious correlation” that results in over-rejection of the null hypothesis. The underlying geometric nature of this problem
is clarified by illustrative examples. The paper concludes with a brief discussion of some possible remedies for this problem. 相似文献
15.
The assessment of OpenStreetMap (OSM) data quality has become an interdisciplinary research area over the recent years. The question of whether the OSM road network should be updated through periodic data imports from public domain data, or whether the currency of OSM data should rather rely on more traditional data collection efforts by active contributors, has led to perpetual debates within the OSM community. A US Census TIGER/Line 2005 import into OSM was accomplished in early 2008, which generated a road network foundation for the active community members in the US. In this study we perform a longitudinal analysis of road data for the US by comparing the development of OSM and TIGER/Line data since the initial TIGER/Line import. The analysis is performed for the 50 US states and the District of Columbia, and 70 Urbanized Areas. In almost all tested states and Urbanized Areas, OSM misses roads for motorized traffic when compared with TIGER/Line street data, while significant contributions could be observed in pedestrian related network data in OSM compared with corresponding TIGER/Line data. We conclude that the quality of OSM road data could be improved through new OSM editor tools allowing contributors to trace current TIGER/Line data. 相似文献
16.
Accurate upward continuation of gravity anomalies supports future precision, free-inertial navigation systems, since the latter
cannot by themselves sense the gravitational field and thus require appropriate gravity compensation. This compensation is
in the form of horizontal gravity components. An analysis of the model errors in upward continuation using derivatives of
the standard Pizzetti integral solution (spherical approximation) shows that discretization of the data and truncation of
the integral are the major sources of error in the predicted horizontal components of the gravity disturbance. The irregular
shape of the data boundary, even the relatively rough topography of a simulated mountainous region, has only secondary effect,
except when the data resolution is very high (small discretization error). Other errors due to spherical approximation are
even less important. The analysis excluded all measurement errors in the gravity anomaly data in order to quantify just the
model errors. Based on a consistent gravity field/topographic surface simulation, upward continuation errors in the derivatives
of the Pizzetti integral to mean altitudes of about 3,000 and 1,500 m above the mean surface ranged from less than 1 mGal
(standard deviation) to less than 2 mGal (standard deviation), respectively, in the case of 2 arcmin data resolution. Least-squares
collocation performs better than this, but may require significantly greater computational resources. 相似文献
17.
Pierre Bosser Olivier Bock Christian Thom Jacques Pelon Pascal Willis 《Journal of Geodesy》2010,84(4):251-265
This paper investigates the impact of rapid small-scale water vapor fluctuations on GPS height determination. Water vapor
measurements from a Raman lidar are used for documenting the water vapor heterogeneities and correcting GPS signal propagation
delays in clear sky conditions. We use data from four short observing sessions (6 h) during the VAPIC experiment (15 May–15
June 2004). The retrieval of wet delays from our Raman lidar is shown to agree well with radiosonde retrievals (bias and standard
deviation (SD) were smaller than 1 and 2.8 mm, respectively) and microwave radiometers (from two different instruments, bias
was 6.0/−6.6 mm and SD 1.3/3.8 mm). A standard GPS data analysis is shown to fail in accurately reproducing fast zenith wet
delay (ZWD) variations. The ZWD estimates could be improved when mean post-fit phase residuals were removed. Several methodologies
for integrating zenith lidar observations into the GPS data processing are also presented. The final method consists in using
lidar wet delays for correcting a priori the GPS phase observations and estimating a scale factor for the lidar wet delays
jointly with the GPS station position. The estimation of this scale factor allows correcting for a mis-calibration in the
lidar data and provides in the same way an estimate of the Raman lidar instrument constant. The agreement of this constant
with an independent determination using radiosonde data is at the level of 1–4%. The lidar wet delays were derived by ray-tracing
from zenith pointing measurements: further improvement in GPS positioning is expected from slant path lidar measurements that
would properly account for water vapor anisotropy. 相似文献
18.
19.
Croft William Lee Shi Wei Sack Jörg-Rüdiger Corriveau Jean-Pierre 《Journal of Geographical Systems》2017,19(3):221-248
Journal of Geographical Systems - Given the large volumes of detailed data now being collected, there is a high demand for the release of this data for research purposes. In particular,... 相似文献
20.
The alignments of the strapdown inertial navigation system (SDINS) utilizing GPS carrier phase rate measurements is introduced. In this paper, a measurement model of GPS carrier phase rate under two antenna configurations is derived in order to be used for the SDINS alignment process. For in-flight alignment, the performance of the proposed SDINS/GPS integration method is analyzed using the covariance analysis and the overall performance is briefly confirmed by the navigation result of a van test. Furthermore, we find that during in-flight alignment the proposed SDINS/GPS integrated system using GPS carrier phase rate measurements can be implemented in real time because the integer ambiguity problem resulting from carrier phase measurements is avoided. 相似文献