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在进行GPS高程拟合时,如果所用函数模型中未知参数个数不恰当,或者随机模型中采用了一个不合理的权阵,都将导致所建数学模型和客观实际存在较大偏差,而影响最终的拟合精度。文中研究了GPS高程拟合时对所建立的数学模型进行参数优化选择和稳健估计,计算数据表明该方法比常规方法在精度上有所提高。 相似文献
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Knowledge graphs are a key technique for linking and integrating cross-domain data, concepts, tools, and knowledge to enable data-driven analytics. As much of the world's data have become massive in size, visualizing graph entities and their interrelationships intuitively and interactively has become a crucial task for ingesting and better utilizing graph content to support semantic reasoning, discovering hidden knowledge discovering, and better scientific understanding of geophysical and social phenomena. Despite the fact that many such phenomena (e.g., disasters) have clear spatial footprints and geographic properties, their location information is considered only as a textual label in existing graph visualization tools, limiting their capability to reveal the geospatial distribution patterns of the graph nodes. In addition, most graph visualization techniques rely on 2D graph visualization, which constrains the dimensions of information that can be presented and lacks support for graph structure examination from multiple angles. To tackle the above challenges, we developed a novel 3D map-based graph visualization algorithm to enable interactive exploration of graph content and patterns in a spatially explicit manner. The algorithm extends a 3D force directed graph by integrating a web map, an additional geolocational force, and a force balancing variable that allows for the dynamic adjustment of the 3D graph structure and layout. This mechanism helps create a balanced graph view between the semantic forces among the graph nodes and the attractive force from a geolocation to a graph node. Our solution offers a new perspective in visualizing and understanding spatial entities and events in a knowledge graph. 相似文献
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为了提高变形监测中地铁隧道断面点截取的效率,文章提出了基于kd-tree和法向量估计的局部点云简化方法,对BaySAC算法的三维激光点云二次参数曲面拟合方法进行改进:利用kd-tree建立点云数据的空间拓扑关系,计算出每个数据点的k邻域;然后使用平面拟合方法获取法矢量;最后根据点云数据法矢量变化程度,采用法矢量自适应得到压缩后的点云数据。实验证明该方法既能较大程度地简化点云,简化结果比较均匀,又具有不破坏细小特征的特点,进一步改进了BaySAC算法的二次参数曲面拟合方法。 相似文献
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Space born systems like Geoscience Laser Altimeter System (GLAS) onboard collect data for ice, cloud and Land. Elevation satellite
(ICESat) collects an unparalleled data set as waveform over terrestrial targets, helps in evaluating the global elevation
data. In this study we compared the Digital Elevation Surface (DES) generated by Cartosat-1 point data and DES generated by
merging the Cartosat-1 data with ICESat data. Outputs in the form of interpolated surfaces were evaluated with the help of
differential global positioning system (DGPS) points collected from study area. The study showed the results that the DES
generated from Cartosat — 1 data had less elevation accuracy when compared with the DGPS data. While merging Cartosat-1 point
height data with ICESat/GLAS data resulted in better accuracy. On the practical side for processing the interpolation, based
on the research the ICESat /GLAS with Cartosat-1 height data can produce better DES compared to the Cartosat-1 stereo data.
The DES was generated using geostatistical interpolation methods in which the global polynomial method proved to be the better
for generating the surface compare to other interpolation techniques studied in this work. For co-kriging method, the accuracy
decreases compare to the kriging interpolation, due to the complexity of parameters that were used for interpolation. On the
theory side, based on this research the statement of which interpolation technique is better than the other cannot be mentioned
easily, because these are based on the data type, parameters and also on method of interpolation. So research experiment should
be more intensely and with more focused. 相似文献
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针对现有三维建筑物变化检测中高度差阈值确定方法存在主观性强、阈值通用性差的问题,本文提出了一种基于正态分布的高度差阈值确定方法。借鉴二维变化检测中变化和未变化像元差值服从正态分布的理论,首先,假设2期DSM高度差服从或近似服从正态分布,并分析了变化和未变化区域高度差的分布;然后,基于拉依达准则提出了利用期望和标准差计算高度差阈值的方法;最后,利用滑动窗口动态计算待检测区域高度差阈值。在2个试验区内,基于本文阈值方法的建筑物变化检测结果较经验阈值方法在完整率、正确率和检测质量上分别平均提高了7.2%、1.5%和7.8%,说明该方法具有较好的通用性。 相似文献
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建筑物高度信息的获取是高分辨率遥感影像信息提取研究中的热点问题之一。该文提出了一套结合面向对象分类方法的建筑物高度反演技术方法。首先,利用建筑物和阴影的形态学指数,通过面向对象分类方法提取建筑物轮廓和阴影信息;然后,采用相交线平均法计算阴影长度;最后,根据阴影长度和建筑物高度的几何关系模型计算建筑物高度。采用西安市的国产资源三号(ZY-3)卫星遥感数据进行提取试验,通过171栋建筑物的实际测量高度对结果进行验证,获得了91.23%的总体精度,显示出该方法在建筑物高度信息提取研究方面具有一定的现实意义。 相似文献
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The paper presents a cycle graph analysis approach to the automatic reconstruction of 3D roof models from airborne laser scanner data. The nature of convergences of topological relations of plane adjacencies, allowing for the reconstruction of roof corner geometries with preserved topology, can be derived from cycles in roof topology graphs. The topology between roof adjacencies is defined in terms of ridge-lines and step-edges. In the proposed method, the input point cloud is first segmented and roof topology is derived while extracting roof planes from identified non-terrain segments. Orientation and placement regularities are applied on weakly defined edges using a piecewise regularization approach prior to the reconstruction, which assists in preserving symmetries in building geometry. Roof corners are geometrically modelled using the shortest closed cycles and the outermost cycle derived from roof topology graph in which external target graphs are no longer required. Based on test results, we show that the proposed approach can handle complexities with nearly 90% of the detected roof faces reconstructed correctly. The approach allows complex height jumps and various types of building roofs to be firmly reconstructed without prior knowledge of primitive building types. 相似文献
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A spatially explicit reinforcement learning model for geographic knowledge graph summarization 总被引:1,自引:0,他引:1
Web‐scale knowledge graphs such as the global Linked Data cloud consist of billions of individual statements about millions of entities. In recent years, this has fueled the interest in knowledge graph summarization techniques that compute representative subgraphs for a given collection of nodes. In addition, many of the most densely connected entities in knowledge graphs are places and regions, often characterized by thousands of incoming and outgoing relationships to other places, actors, events, and objects. In this article, we propose a novel summarization method that incorporates spatially explicit components into a reinforcement learning framework in order to help summarize geographic knowledge graphs, a topic that has not been considered in previous work. Our model considers the intrinsic graph structure as well as the extrinsic information to gain a more comprehensive and holistic view of the summarization task. By collecting a standard data set and evaluating our proposed models, we demonstrate that the spatially explicit model yields better results than non‐spatial models, thereby demonstrating that spatial is indeed special as far as summarization is concerned. 相似文献
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This paper presents a fully automatic framework to extract building footprints from a Digital Surface Model (DSM). The proposed approach may be decomposed in two steps, each of them relying on a global optimization solver. The first step aims to extract rectangular building footprints directly from the DSM using a Marked Point Process (MPP) of rectangles. We introduce an energy that prevents overlapping rectangles and aligns rectangle edges with DSM discontinuities. This energy is then embedded in a RJMCMC sampler coupled with a simulated annealing to find its global optimum. Then, the second step of our framework refines these extracted rectangles into polygonal building footprints. We first create an arrangement of line segments supporting the rectangle edges. The dual graph of this arrangement is then considered in a maximum flow optimization scheme to remove edges in the arrangement which do not correspond to building edges in the DSM. Finally, 3D results illustrate a fully automatic process to build a 3D city model from a DSM only. 相似文献
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Journal of Geodesy - ?The application of Stokes' formula to create geoid undulations requires no masses outside the geoid. However, due to the existence of the topography, terrain... 相似文献
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M. K. Paul 《Journal of Geodesy》1973,47(4):413-425
Neglecting distant zones in the computation of geoidal height using Stokes' formula gives rise to some truncation error. This
truncation error is expressible as a weighted summation of the zonal harmonic components of the gravity anomaly. Making use
of the well-known properties of Legendre polynomials, a compact method of computing these theoretical coefficients has been
developed in this paper. 相似文献
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This research proposed a parallelized approach to scaling up the calculation of inundation height, the minimum sea‐level rise required to inundate a cell on a digital elevation model, which is based on Dijkstra's algorithm for shortest‐path calculations on a graph. Our approach is based on the concepts of spatial decomposition, calculate‐and‐correct, and a master/worker parallelization paradigm. The approach was tested using the U.S. Coastal Relief Model (CRM) dataset from the National Geophysical Data Center on a multicore desktop computer and various supercomputing resources through the U.S. Extreme Science and Engineering Discovery Environment (XSEDE) program. Our parallel implementation not only enables computations that were larger than previously possible, but also significantly outperforms serial implementations with respect to running time and memory footprint as the number of processing cores increases. The efficiency of the scalability seemed to be tied to tile size and flattened out at a certain number of workers. 相似文献
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采用RTK/水准确定两套坐标转换模型时,RTK测量的精度限制会降低模型精度.本文经推导论证,通过高程异常模型定位粗差,隔离粗差后可有效提高转换精度.最后通过工程算例验证了该方法的实用性.该技术可应用于不同坐标系坐标转换工作. 相似文献
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Christopher Jekeli 《Journal of Geodesy》1983,57(1-4):10-28
The problem of the divergence of the geopotential spherical harmonic series at the earth's surface is investigated from a numerical, rather than a theoretical, approach. A representative model of the earth's potential is devised on the basis of a density layer, which, in the spherical approximation, generates a gravity field whose harmonic constituents decay according to an accepted degree variance model. This field, expanded to degree 300, and a topographic surface specified to a corresponding resolution of 67 km are used to compute the differences between truncated inner and outer series of the gravity and height anomalies at the surface of the earth model. Up to degree 300, these differences attain RMS values from 0.33 μgal to 86 μgal for the gravity anomaly and from 0.32 μm to 410 μm for the height anomaly, in areas ranging respectively from near the equator to the vicinity of the pole. In addition to these values, there is an expected truncation effect, caused by the neglect of higher degree components of the inner series, of about 30 mgal and 36 cm, respectively. The field is then subjected to a Gaussian filter which effectively cuts off information at degree 300 (at the 5% level). The RMS error to degree 300 is thereby reduced by factors of 10 to 20, with a concomitant reduction in the truncation effect to about 0.3 mgal and 0.7 cm. 相似文献