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971.
We propose a method to automatically register two point clouds acquired with a terrestrial laser scanner without placing any markers in the scene. What makes this task challenging are the strongly varying point densities caused by the line-of-sight measurement principle, and the huge amount of data. The first property leads to low point densities in potential overlap areas with scans taken from different viewpoints while the latter calls for highly efficient methods in terms of runtime and memory requirements.A crucial yet largely unsolved step is the initial coarse alignment of two scans without any simplifying assumptions, that is, point clouds are given in arbitrary local coordinates and no knowledge about their relative orientation is available. Once coarse alignment has been solved, scans can easily be fine-registered with standard methods like least-squares surface or Iterative Closest Point matching. In order to drastically thin out the original point clouds while retaining characteristic features, we resort to extracting 3D keypoints. Such clouds of keypoints, which can be viewed as a sparse but nevertheless discriminative representation of the original scans, are then used as input to a very efficient matching method originally developed in computer graphics, called 4-Points Congruent Sets (4PCS) algorithm. We adapt the 4PCS matching approach to better suit the characteristics of laser scans.The resulting Keypoint-based 4-Points Congruent Sets (K-4PCS) method is extensively evaluated on challenging indoor and outdoor scans. Beyond the evaluation on real terrestrial laser scans, we also perform experiments with simulated indoor scenes, paying particular attention to the sensitivity of the approach with respect to highly symmetric scenes. 相似文献
972.
Philip Claudio Joerg Michael Zemp 《Geografiska Annaler: Series A, Physical Geography》2014,96(2):135-145
Assessments of geodetic volume change are widely used in glaciology and have a long tradition dating back to the nineteenth century. Over time, the geodetic method and corresponding data storage have been developed further, but the resulting methodological heterogeneity can lead to errors that are difficult to separate from other survey uncertainties. In this study we used high‐resolution airborne laser scanning data from the Findelengletscher in the Swiss Alps to evaluate state‐of‐the‐art volumetric glacier change methods. For the first time we have been able to simulate errors arising from different geodetic methods and spatial resolutions. The evaluation showed that, although the digital elevation models were perfectly co‐registered, systematic and random method‐ and scale‐dependent errors still occurred. These errors have an impact on the resulting volume changes at lower spatial resolutions and may lead to exponentially larger uncertainties. Volume changes from contour methods provided reasonably accurate results, while volumetric change assessments from central profile lines were especially prone to biases at any scale. 相似文献
973.
974.
提出一种短弧段ETALON卫星的SLR数据处理策略,仅解算卫星轨道、测站距离偏差、地球自转参数,并利用2018-01~10数据进行验证。结果表明,ETALON-1/2卫星定轨残差RMS分别为1.11 cm、1.08 cm;与IERS-C04 产品相比,短弧段数据解算的Xp、Yp、LOD参数误差RMS分别为2.21 mas、2.26 mas、218.30 μs/d;与ILRS事后最终轨道相比,ETALON-1卫星R、T、N方向轨道精度分别为1.6 cm、8.5 cm、6.8 cm,ETALON-2卫星R、T、N方向轨道精度分别为 2.1 cm、8.9 cm、8.7 cm。 相似文献
975.
Nancy J. McMillan Shannon Rees Kristen Kochelek Catherine McManus 《Geostandards and Geoanalytical Research》2014,38(3):329-343
Laser‐induced breakdown spectroscopy (LIBS) records light emitted from the decay of electrons to lower‐energy orbitals during cooling of laser‐induced ablation plasmas; the resultant spectra can be used in a variety of geoanalytical applications. Four aspects of LIBS analysis distinguish LIBS from traditional laboratory‐based analytical techniques: (i) the lack of necessary sample preparation, allowing rapid analysis of many samples, (ii) the ability to analyse both 20 to 100 μm‐diameter spots and whole rocks, (iii) the detailed chemical signature contained in a LIBS spectrum and (iv) the ability to take LIBS into the field in backpack portable instrumentation. Three case studies illustrate potential applications of LIBS in the geosciences. First, analysis of the Carrizozo basalt flow in New Mexico, USA, illustrated that LIBS spectra could discriminate between samples of similar composition within uncertainties typical of whole‐rock analysis by X‐ray fluorescence spectrometry. Second, spectra from four sets of rubies from Madagascar and Tanzania illustrate the use of LIBS and multivariate analysis to determine provenance with success rates of > 95%. This technique can also be applied to correlation of units. Finally, a chemical map of a copper ore from Butte, MT, USA, illustrates the use of spatially defined LIBS spectra to understand chemical variations within textural context. 相似文献
976.
Barbara A. Cohen J. Scott Miller Zheng‐Hua Li Timothy D. Swindle Renee A. French 《Geostandards and Geoanalytical Research》2014,38(4):421-439
Geochronology is a fundamental measurement for planetary samples, providing global and solar system context for the conditions prevailing on the planet at the time of major geological events. The potassium (K)‐Argon (Ar) laser experiment (KArLE) will make in situ noble gas geochronology measurements aboard planetary robotic missions such as rovers and landers. Laser‐induced breakdown spectroscopy (LIBS) is used to measure the K abundance in a sample and to release its noble gases; the evolved Ar is measured by mass spectrometry, and relative K content is related to absolute Ar abundance by sample mass, determined by optical measurement of the ablated volume. This approach allows K and Ar to be measured on identical volumes multiple times to create an isochron, which improves the age determination and reveals irregularities in the rock if they exist. The KArLE technique measures a whole‐rock K‐Ar age with 10% uncertainty or better for rocks 2 Ga or older, sufficient to resolve the absolute age of many planetary samples. The LIBS–mass spectrometry approach is attractive because the analytical components have been flight‐proven, do not require further technical development and provide essential measurements (complete elemental abundance, evolved volatile analysis, micro‐imaging) as well as in situ geochronology. 相似文献
977.
Klaus Peter Jochum Brigitte Stoll Ulrike Weis Dorrit E. Jacob Regina Mertz‐Kraus Meinrat O. Andreae 《Geostandards and Geoanalytical Research》2014,38(3):265-292
LA‐ICP‐MS is one of the most promising techniques for in situ analysis of geological and environmental samples. However, there are some limitations with respect to measurement accuracy, in particular for volatile and siderophile/chalcophile elements, when using non‐matrix‐matched calibration. We therefore investigated matrix‐related effects with a new 200 nm femtosecond (fs) laser ablation system (NWRFemto200) using reference materials with different matrices and spot sizes from 10 to 55 μm. We also performed similar experiments with two nanosecond (ns) lasers, a 193 nm excimer (ESI NWR 193) and a 213 nm Nd:YAG (NWR UP‐213) laser. The ion intensity of the 200 nm fs laser ablation was much lower than that of the 213 nm Nd:YAG laser, because the ablation rate was a factor of about 30 lower. Our experiments did not show significant matrix dependency with the 200 nm fs laser. Therefore, a non‐matrix‐matched calibration for the multi‐element analysis of quite different matrices could be performed. This is demonstrated with analytical results from twenty‐two international synthetic silicate glass, geological glass, mineral, phosphate and carbonate reference materials. Calibration was performed with the certified NIST SRM 610 glass, exclusively. Within overall analytical uncertainties, the 200 nm fs LA‐ICP‐MS data agreed with available reference values. 相似文献
978.
979.
980.
针对卫星激光测距仪的几个关健设备 ,建立了一套检测系统。介绍了该检测系统的方法、原理以及实际应用情况 相似文献