共查询到20条相似文献，搜索用时 46 毫秒
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广义球谐函数及其在梯度边值问题的应用 总被引：1，自引：0，他引：1
本文首先指出球谐函数不是球面上唯一的正交函数系,接着证明了体谐函烽的一阶,二阶水平导数也是球面上的正交函数系,最后利用球面上的正交函数系研究了物理大地测量中的二阶,二阶梯度边值问题。 相似文献
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根据经典的球谐函数方法,为满足正交化要求,观测数据需要覆盖整个球面,而对于地表局部测量数据,则无法应用球谐方法解算重力场模型。针对此问题,采用Slepian局部谱分析方法解算中国大陆范围内的实测重力场变化数据,并以GOCE卫星球谐函数解作为已知模型,评估由于实际陆地重力测点的非均匀分布对球谐函数解的误差影响。通过计算多个阶次中国大陆局部范围的Slepian基函数分布;采用GOCE卫星获得重力场模型的前72阶球谐系数作为已知结果,评价实际测点非均匀分布的解算有效性,并针对中国大陆地区采用Slepian基函数进行解算,通过模型对比选择最优截段项数;针对2005—2008年中国大陆地区流动重力测量获得的重力场变化信号进行解算,获得了72阶重力场变化模型。 相似文献
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球冠谐分析中非整阶Legendre函数的性质及其计算 总被引：9，自引：4，他引：5
局部重力场的谱方法是当前重力学的研究方向,该方法的核心问题是如何构造合适的谱函数以及如何对谱函数实施快速、有效的计算。当所研究的区域近似一个球冠时,迂冠谐函数是该区域对应的谱函数,它由非整阶勒让德（Ｌｅｇｅｎｄｒｅ）函数和三角函数组成,显然非整阶勒让德函数的构造和计算是研究球冠谐函数的关键。本文研究了非高小阶勒让德函数的性质和实用计算方法,包括如何对非整阶勒让德函数实施规格化处理。 相似文献
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张瑞华 《解放军测绘研究所学报》2000,20(2):7-14
本文详细推导了地球引力加速度及其偏导数的计算公式,给出了一组用来计算正规化球谐函数的递推关系。这组递推关系优于一般文献上所给出的用来计算非正规化球谐函数的递推关系,它避免了由于不同阶、级非正规化球谐函数数值相差过大而引起的计算精度的损失。在卫星精密轨道确定中已经证明这种算法是非常有效的。 相似文献
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扰动重力梯度的非奇异表示 总被引：5，自引：0，他引：5
在局部指北坐标系中用地心球坐标来表示扰动重力梯度张量，当计算点趋近于两极时，由于Legendre函数的一阶和二阶导数以及分母上所含余纬的正弦函数，将导致扰动重力梯度张量的计算出现无穷大。因此，本文引入了Legendre函数的一阶和二阶导数以及 无奇异性的计算公式，并且进一步推导了 无奇异性的计算公式。在将Legendre函数的一阶和二阶导数以及 、 无奇异性的计算公式代入到扰动重力梯度张量各分量的求解中时，又充分考虑了m等于0，1，2以及其它量时的复杂情况，建立了扰动重力梯度张量各分量无奇异性的详细计算模型。通过模拟实验表明，本文所建立的详细计算模型不仅能够完全满足当前卫星重力梯度张量计算的精度要求，而且模型稳定、可靠、易于编程实现。 相似文献
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球谐函数变换快速计算扰动引力 总被引：1，自引：0，他引：1
在球谐函数变换基础上,利用新极下轨道的特殊性,在新坐标下引入Clenshaw求和计算轨道扰动引力。从理论上对比分析了传统方法、球谐函数变换方法和改进方法的计算速度和存储模型需要的物理空间。模拟试验分别采用3种方法计算了一段轨道的扰动引力,试验结果表明,改进的球谐函数变换方法比传统球谐函数变换方法计算速度可提高100倍,数据存储量仅占传统方法的3%。 相似文献
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基于移去计算恢复技术(RCR),结合中国近海区域Sandwell测高重力数据,分析了VK和FEO核函数不同阶数条件下,球冠半径大小对残余大地水准面结果的影响。结果表明,在本测试区域,当核函数阶数较大时(P=L=90和P=L=120),球冠半径的增加对残余大地水准面的影响不显著。综合低阶核函数和较高阶核函数的计算结果,球冠半径为3°是一个较优参数。利用GPS水准数据对计算结果进行检核表明,采用改进的椭球核函数比球面核函数计算精度可以提高1.5cm。 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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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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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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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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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