共查询到20条相似文献，搜索用时 46 毫秒
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在水下定位过程中,对于任意给定的浮标数目n(n≥4),嵌套圆锥构型可给出一类最小GDOP定位图形。但由于定位浮标均需布设于同一水平面而导致共面约束,在由定位浮标和水下目标点构成的定位图形中,其GDOP达不到理论最小值, 在该约束条件下水下定位浮标阵列GDOP最小化问题有待研究。本文通过介绍GDOP密度来衡量浮标阵列的定位能力。为降低嵌套圆锥构型GDOP最优问题的可行域,把定位浮标数n整数分解,基于最小PDOP定位图形的极值条件,寻找每组浮标组合圆锥构型GDOP密度的局域最优解,然后从候选的所有浮标组合构型中寻找GDOP密度最小的全局最优解。最后分别以6~8枚浮标为例,给出了它们水下定位浮标阵列的最佳嵌套圆锥构型。 相似文献
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由正交三角函数导出了一类最小GDOP测距单点定位构型集。导出了测距单点定位构型的GDOP极小值条件,并由此引入了最小GDOP测距单点定位构型解集的概念,揭示了最小GDOP测距单点定位构型的性质——旋转不变性和叠加不变性。对于任意给定的控制点数目n,由正交三角函数导出了最小GDOP构型的正多边形解。最后在最小GDOP二维测距单点定位构型的基础上,导出了三种三维最小GDOP测距单点定位构型:圆锥构型(锥角108.48°)、笛卡尔构型、Walker构型(轨道倾角54.74°),这些构型的几何条件为讨论GNSS星座设计提供了参考。 相似文献
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基于STK的全球卫星导航定位系统DOP值仿真 总被引：1，自引：0，他引：1
通过STK卫星数据库建立了GPS卫星星座；根据GALILEO卫星设计参数，利用轨道向导建立GALILEO卫星星座。比较了武汉地区GPS、GALILEO、GPS和GALILEO组合的卫星可见数和GDOP值，以及全球GDOP值的分布。 相似文献
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在圆锥构型的基础上,定义了一种嵌套圆锥构型,并导出了最小PDOP嵌套圆锥构型所应满足的条件。讨论了构造最小GDOP(几何精度衰减因子)构型的方法。在最小PDOP嵌套圆锥构型的基础上给出了最小GDOP嵌套圆锥构型。在此基础上,由最小GDOP嵌套圆锥构型导出了数学上仅有的5种正多面体构型,证明了5种正多面体均满足GDOP极值条件。 相似文献
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采用多卫星导航系统组合导航,定位精度和系统可靠性会大幅提升,但导航定位运算量也会成倍增长。为解决多系统组合导航定位精度与实时性之间的矛盾,提出一种新的选星方法。新方法不追求最小GDOP值,而是以满足导航定位精度的GDOP值为前提,结合模糊理论中隶属函数的思想,按卫星在星座中均匀分布为原则进行选星。推导伪距测量的误差模型,分析了GDOP与测量误差之间的关系。北斗、GPS和GLONASS三系统组合导航选星实验结果表明,在不超过3次求解GDOP值的情况下,新方法能以不小于98%的概率得到GDOP≤4。 相似文献
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全球导航卫星系统（global navigation satellite system，GNSS）/声纳水下定位精度主要取决于GNSS浮标阵列构型和声学测距精度。优化水面浮标阵列是提高水下定位精度的重要途径。探讨了GNSS浮标阵列解析优化方法，算例以5枚和6枚浮标布设为例，应用所提方法给出了最优浮标阵列解。基于几何精度因子（geometric dilution of precision，GDOP）最小构型解析方法，通过考虑水下定位GNSS浮标位于水面和存在高度角限制这一约束条件，对水下定位浮标阵列进行了解析优化。由于浮标进行水下定位时是范围性的，还基于区域GDOP均值和方差两个指标对GNSS浮标阵优化问题进行了探讨，并采用数值方法设计了区域GDOP均值最小构型搜索算法。研究表明，虽然存在高度角约束条件，最优浮标阵列几何结构并不唯一，若在此基础上进一步考虑区域GDOP均值和方差最小的目标，则最终可获得唯一的区域均值浮标阵列结构。 相似文献
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《武汉大学学报(信息科学版)》2016,(3)
几何精度衰减因子(GDOP)是衡量定位构型优劣的重要指标,探讨最小GDOP定位构型的几何结构在单GNSS星座设计和多系统组合优化方面具有现实意义。在GNSS普遍采用的Walker构型的基础上,导出了最小GDOP组合Walker构型所应满足的条件方程。讨论了单一和组合Walker构型的GDOP地表覆盖性质。最后,通过仿真分析验证了主要结论。 相似文献
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随着各国卫星导航系统的建设与完善,同一历元的可见卫星数目逐渐增加,如何对众多卫星进行选择以优化利用现有资源便显得迫切而重要。本文以获得满足设计要求的GDOP为前提,根据各时刻可见卫星数量的大小,选择适合的遮蔽仰角,以卫星空间构型的体积与GDOP关系为依据,引入计算几何学中解决三维点集的凸壳问题的增量算法,并结合导航卫星星座的自身特点,提出了对卫星位置坐标直接进行选择的一种快速次优的选星算法。实验结果表明,在GDOP满足要求且选星数较少的情况下,相对传统GDOP选星法大大减小了计算量,该方法简洁快速,能有效满足选星求解的实时性和精度要求。 相似文献
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Monitoring drought dynamics in the Aravalli region (India) using different indices based on ground and remote sensing data 总被引：5，自引：0，他引：5
C. Bhuiyan R.P. Singh F.N. Kogan 《International Journal of Applied Earth Observation and Geoinformation》2006,8(4):289-302
The hard-rock hilly Aravalli terrain of Rajasthan province of India suffers with frequent drought due to poor and delayed monsoon, abnormally high summer-temperature and insufficient water resources. In the present study, detailed analysis of meteorological and hydrological data of the Aravalli region has been carried out for the years 1984–2003. Standardised Precipitation Index (SPI) has been used to quantify the precipitation deficit. Standardised Water-Level Index (SWI) has been developed to assess ground-water recharge-deficit. Vegetative drought indices like Vegetation Condition Index (VCI) and Temperature Condition Index (TCI) and Vegetation Health Index (VHI) have been computed using NDVI values obtained from Global Vegetation Index (GVI) and thermal channel data of NOAA AVHRR satellite. Detailed analyses of spatial and temporal drought dynamics during monsoon and non-monsoon seasons have been carried out through drought index maps generated in Geographic Information Systems (GIS) environment. Analysis and interpretation of these maps reveal that negative SPI anomalies not always correspond to drought. In the Aravalli region, aquifer-stress shifts its position time to time, and in certain pockets it is more frequent. In comparison to hydrological stress, vegetative stress in the Aravalli region is found to be slower to begin but quicker to withdraw. 相似文献
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SVG是一种基于XML的用来描述二维矢量图形和矢量/栅格混合图形的标记语言,虽然SVG不是为了面向地理空间数据发布而制定的标准,但它的许多特性都能被广泛地应用到WebGIS中,从而实现矢量WebGIS。由于SVG通过简单的文本语句描述矢量图像,所以SVG通常数据量很小,并且SVG支持GZIP压缩,所以基于SVG构建WebGIS能减轻网络传输负载,加快地图显示速度。SVG内置了对JavaScript的支持,且SVG可通过DOM解析映像成内存中的树型结构,所以客户层可通过JavaScript对DOM的操作实现对地图的缩放、漫游、查询、图层控制等交互操作。 相似文献
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本文在讨论DDE技术的基础上，对MapInfo的DDE机制的实现作了探讨和分析。根据技园区域GIS的实际开发工作，介绍了利用DDE技术在MapInfo中成功地集成Foxpro和Autocad. 相似文献
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遥感技术在土地利用动态监测中的应用 总被引：8，自引：0，他引：8
金时华 《测绘与空间地理信息》2006,29(1):98-101
主要论述遥感技术在土地监测中的应用,以某地区土地利用动态遥感监测研究项目的运作过程为例进行阐述。首先介绍了土地利用动态监测的具体内容和技术路线。其次,对数据预处理与信息采集的方法与手段进行了探讨。最后,对作业的内、外业主要过程以及应提交的成果作了介绍。 相似文献
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地理数据库的关系模型及其实现 总被引：1，自引：0，他引：1
本文从以图论观点分析地理实体入手,系统阐述了地理数据库关系模型的设计法和过程。作者于1984年4～9月间在微型机上设计建立了关系型地理数据库的实方验系统(RGDB)。该系统采用了本文提出的关系模型,采用了可动态扩库的子库组合结构,这种结构具有灵活性和提高空间利用率的优点。RGDB含有多种功能的数据操作命令,除了具有一般检索功能外,还能进行“开窗”选取和十分“自由”的映象选取。本文对RGDB系统的主要性能和实现途径作了扼要介绍。 相似文献
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Automatic 3D extraction of building roofs from remotely sensed data is important for many applications including city modelling. This paper proposes a new method for automatic 3D roof extraction through an effective integration of LIDAR (Light Detection And Ranging) data and multispectral orthoimagery. Using the ground height from a DEM (Digital Elevation Model), the raw LIDAR points are separated into two groups. The first group contains the ground points that are exploited to constitute a ‘ground mask’. The second group contains the non-ground points which are segmented using an innovative image line guided segmentation technique to extract the roof planes. The image lines are extracted from the grey-scale version of the orthoimage and then classified into several classes such as ‘ground’, ‘tree’, ‘roof edge’ and ‘roof ridge’ using the ground mask and colour and texture information from the orthoimagery. During segmentation of the non-ground LIDAR points, the lines from the latter two classes are used as baselines to locate the nearby LIDAR points of the neighbouring planes. For each plane a robust seed region is thereby defined using the nearby non-ground LIDAR points of a baseline and this region is iteratively grown to extract the complete roof plane. Finally, a newly proposed rule-based procedure is applied to remove planes constructed on trees. Experimental results show that the proposed method can successfully remove vegetation and so offers high extraction rates. 相似文献
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遥感和GIS技术应用于伊拉克南部Basrah省土地利用/覆盖变化及城市扩张研究(英文) 总被引：2，自引：0，他引：2
In recent years, land use/cover dynamic change has become a key subject that needs to be dealt with in the study of global
environmental change. In this paper, remote sensing and geographic information systems (GIS) are integrated to monitor, map,
and quantify the land use/cover change in the southern part of Iraq (Basrah Province was taken as a case) by using a 1:250
000 mapping scale. Remote sensing and GIS software were used to classify Landsat TM in 1990 and Landsat ETM+ in 2003 imagery
into five land use and land cover (LULC) classes: vegetation, sand, urban area, unused land, and water bodies. Supervised
classification and normalized difference build-up index (NDBI) were used respectively to retrieve its urban boundary. An accuracy
assessment was performed on the 2003 LULC map to determine the reliability of the map. Finally, GIS software was used to quantify
and illustrate the various LULC conversions that took place over the 13-year span of time. Results showed that the urban area
had increased by the rate of 1.2% per year, with area expansion from 3 299.1 km2 in 1990 to 3 794.9 km2 in 2003. Large vegetation area in the north and southeast were converted into urban construction land. The land use/cover
changes of Basrah Province were mainly caused by rapid development of the urban economy and population immigration from the
countryside. In addition, the former government policy of “returning farmland to transportation and huge expansion in military
camps” was the major driving force for vegetation land change. The paper concludes that remote sensing and GIS can be used
to create LULC maps. It also notes that the maps generated can be used to delineate the changes that take place over time.
Supported by the Al-Basrah University, Iraq, the Geo-information Science and Technology Program (No. IRT 0438)China). 相似文献
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随着城市面貌日新月异,地下管网的建设也在持续推进,作为城市的地下“神经网络”,全天24 h保障城市的正常运转和发展。本文以实现城市管网管理系统的高可用、无插件、智能化为目标,采用“地上地下一体”“二三维一体”的设计理念,研究基于WebGL的三维智慧管网系统的关键技术,实现了管线设施管理的信息数字化、空间化与图形化。 相似文献
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We aim a better understanding of the effect of spring-time snow melt on the remotely sensed scene reflectance by using an extensive amount of optical spectral data obtained from an airborne hyperspectral campaign in Northern Finland. We investigate the behaviour of thin snow reflectance for different land cover types, such as open areas, boreal forests and treeless fells. Our results not only confirm the generally known fact that the reflectance of a melting thin snow layer is considerably lower than that of a thick snow layer, but we also present analyses of the reflectance variation over different land covers and in boreal forests as a function of canopy coverage. According to common knowledge, the highly variating reflectance spectra of partially transparent, most likely also contaminated thin snow pack weakens the performance of snow detection algorithms, in particular in the mapping of Fractional Snow Cover (FSC) during the end of the melting period. The obtained results directly support further development of the SCAmod algorithm for FSC retrieval, and can be likewise applied to develop other algorithms for optical satellite data (e.g. spectral unmixing methods), and to perform accuracy assessments for snow detection algorithms.A useful part of this work is the investigation of the competence of Normalized Difference Snow Index (NDSI) in snow detection in late spring, since it is widely used in snow mapping. We conclude, based on the spectral data analysis, that the NDSI -based snow mapping is more accurate in open areas than in forests. However, at the very end of the snow melting period the behavior of the NDSI becomes more unstable and unpredictable in non-forests with shallow snow, increasing the inaccuracy also in non-forested areas. For instance in peatbogs covered by melting snow layer (snow depth < 30 cm) the mean NDSI -0.6 was observed, having coefficient of variation as high as 70%, whereas for deeper snow packs the mean NDSI shows positive values. 相似文献