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11.
The application of low-cost L1 GPS receivers integrated with micro-electro-mechanical system (MEMS) inertial measurement units
(IMU) allows the continuous observation of position, velocity and orientation which opens new possibilities for comparison
of athletes’ performance throughout a racecourse. In this paper, we compare loosely and closely coupled integration strategies
under realistic racing scenarios when GPS is partially or completely masked. The study reveals that both integration approaches
have a similar performance when the satellite constellation is completed or the outages are short. However, for less than
four satellites, the closely coupled strategy clearly outperforms the loosely coupled approach. The second part of the paper
is devoted to the important problem of system initialization, because the conventional GPS/IMU alignment methods are no longer
applicable when using MEMS-IMU. We introduce a modified coarse alignment method and a quaternion estimation method for the
computation of the initial orientation. Simulations and practical experiments reveal that both methods are numerically stable
for any initial orientation of the sensors with the error characteristics of MEMS-IMUs. Throughout the paper, our findings
are supported by racing experiments with references provided in both, the measurement and the navigation domains. 相似文献
12.
Jochem Verrelst Gertjan W. Geerling Karle V. Sykora Jan G.P.W. Clevers 《International Journal of Applied Earth Observation and Geoinformation》2009
Combined optical and laser altimeter data offer the potential to map and monitor plant communities based on their spectral and structural characteristics. A problem unresolved is, however, that narrowly defined plant communities, i.e. plant communities at a low hierarchical level of classification in the Braun-Blanquet system, often cannot be linked directly to remote sensing data for vegetation mapping. We studied whether and how a floristic dataset can be aggregated into a few major discrete, mappable classes without substantial loss of ecological meaning. Multi-source airborne data (CASI and LiDAR) and floristic field data were collected for a floodplain along the river Waal in the Netherlands. Mapping results based on floristic similarity alone did not achieve highest levels of accuracy. Ordination of floristic data showed that terrain elevation and soil moisture were the main underlying environmental drivers shaping the floodplain vegetation, but grouping of plant communities based on their position in the ordination space is not always obvious. Combined ordination-based grouping with floristic similarity clustering led to syntaxonomically relevant aggregated plant assemblages and yielded highest mapping accuracies. 相似文献
13.
针对一些测绘工作者对RTK测量精度的疑虑,本文设计了一套检验RTK在几种常见作业环境下测量精度的实验方案,分别进行了内符合精度和外符合精度分析。结论表明:在几种常见工作环境下,RTK测量给出的测量精度可靠,高程与平面精度均能小于5cm。 相似文献
14.
Jan Kouba 《GPS Solutions》2002,5(3):88-90
The GPS Toolbox is dedicated to highlighting algorithms and source code utilized by GPS engineers and scientists. If you have
an interesting subroutine or program you would like to share with our readers, please pass it along so that we might continue
to bring you this column; e-mail it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here,
or to leave a request for a piece of source code you may be looking for, visit our web site at http:/www.ngs.noaa.gov/gps-toolbox.
This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic
Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada. ? 2002 Wiley Periodicals, Inc. 相似文献
15.
Attitude estimation based on fusion of gyroscopes and single antenna GPS for small UAVs under the influence of vibration 总被引:2,自引:2,他引:2
An attitude estimation method is presented for small unmanned aerial vehicles (UAVs) powered by a piston engine which is the
major source of vibration. Vibration of the engine significantly degrades the accuracy of the inertial measurement unit, especially
for low-cost sensors that are based on micro electro-mechanical system. Therefore, a vibration model for a small UAV is proposed
in order to examine the influence of vibration on attitude estimation with different sensors. The model is derived based on
spectrum analysis with short-time Fourier transform. The vibration is compared with the drift of the gyroscope in order to
examine the impact on attitude estimation. An attitude estimation method that fuses the gyroscopes and single antenna global
positioning system (GPS) is proposed to mitigate the influence of engine vibration and gyroscope drift. The quaternion-based
extended Kalman filter is implemented to fuse the sensors. This filter fuses the angular rates measured by the gyroscopes
and the pseudo-attitude derived from the GPS velocity to estimate the attitude of the UAV. Simulations and experiment results
indicate that the proposed method performs well both in short-term and long-term accuracy even though the gyroscopes are affected
by drift and vibration noise, while the pseudo-attitude contains severe noise. 相似文献
16.
Acquisition and registration of terrestrial 3D laser scans is a fundamental task in mapping and modeling of cities in three dimensions. To automate this task marker-free registration methods are required. Based on the existence of skyline features, this paper proposes a novel method. The skyline features are extracted from panoramic 3D scans and encoded as strings enabling the use of string matching for merging the scans. Initial results of the proposed method in the old city center of Bremen are pre-sented. 相似文献
17.
Gerard W. Hazeu Arnold K. Bregt Allard J.W. de Wit Jan G.P.W. Clevers 《International Journal of Applied Earth Observation and Geoinformation》2011
Land cover and land use are important information sources for environmental issues. One of the most important changes at the Earth's surface concerns land cover and land use. Knowledge about the location and type of these changes is essential for environmental modeling and management. Remote sensing data in combination with additional spatial data are recognized as an important source of information to detect these land cover and land use changes. 相似文献
18.
Remotely sensed estimation of forest canopy density: A comparison of the performance of four methods
Chudamani Joshi Jan De Leeuw Andrew K. Skidmore Iris C. van Duren Henk van Oosten 《International Journal of Applied Earth Observation and Geoinformation》2006
In recent years, a number of alternative methods have been proposed to predict forest canopy density from remotely sensed data. To date, however, it remains difficult to decide which method to use, since their relative performance has never been evaluated. In this study the performance of: (1) an artificial neural network, (2) a multiple linear regression, (3) the forest canopy density mapper and (4) a maximum likelihood classification method was compared for prediction of forest canopy density using a Landsat ETM+ image. Comparison of confusion matrices revealed that the regression model performed significantly worse than the three other methods. These results were based on a z-test for comparison of weighted kappa statistics, which is an appropriate statistic for analysis of ranked categories. About 89% of the variance of the observed canopy density was explained by the artificial neural networks, which outperformed the other three methods in this respect. Moreover, the artificial neural networks gave an unbiased prediction, while other methods systematically under or over predicted forest canopy density. The choice of biased method could have a high impact on canopy density inventories. 相似文献
19.
Jan Pisek Jing M. Chen Roselyne Lacaze Oliver Sonnentag Krista Alikas 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(4):341-346
The clumping index measures the spatial aggregation (clumped, random and regular) of foliage elements. The global mapping of the clumping index with a limited eight-month multi-angular POLDER 1 dataset is expanded by integrating new, complete year-round observations from POLDER 3. We show that terrain-induced shadows can enhance bi-directional reflectance distribution function variation and negatively bias the clumping index (i.e. indicating more vegetation clumping) in rugged terrain. Using a global high-resolution digital elevation model, a topographic compensation function is devised to correct for this terrain effect. The clumping index reductions can reach up to 30% from the topographically non-compensated values, depending on terrain complexity and land cover type. The new global clumping index map is compared with an assembled set of field measurements from 32 different sites, covering four continents and diverse biomes. 相似文献
20.