Fast space-domain evaluation of geodetic surface integrals     

R. Lehmann 《Journal of Geodesy》1997,71(9):533-540

Geodetic surface integrals play an important role in the numerical solution of geodetic boundary-value problems. In many cases they can be evaluated using fast methods in the frequency domain (FFT). However, this is not possible in general, because the domain of integration may be non-trivial (as is the surface of the Earth), the kernel function may not be of convolution type, or the data distribution may be heterogeneous. Therefore, fast evaluation strategies are also required in the space domain. They are more difficult to design because only one property is left where a more or less fast evaluation strategy can be built upon: the potential type of the kernel function. Consequently, the idea is not to replace well-established frequency domain techniques, but to supplement them. Our approach to this problem goes in two directions: (1) we use advanced cubature methods where the integration nodes automatically densify in the vicinity of the evaluation points; (2) we use powerful computer hardware, namely MIMD computers with distributed memory. This enables us to evaluate geodetic surface integrals of any practical complexity in reasonable time and accuracy. This is shown in a numerical example. Received: 7 May 1996 / Accepted:17 March 1997  相似文献   

一种符合视觉规律的,基于地图数据的虚拟地景仿真   总被引：5，自引：1，他引：5  

陈刚 《测绘学报》1997,26(3):241-246

本文分析和解决了两个关键性问题，使计算机所生成的虚拟地景符合人的“越近看得越清”视觉规律，并通过实例对该方法的实现过程给予了详细的描述。  相似文献   

山区河流准三维水沙输运与河床演变模拟   总被引：1，自引：0，他引：1  

程根伟 《山地学报》2001,19(3):207-212

在渠道水力学和河流动力学研究的基础上，对不规则河流形态下的纵向流速分布和弯道水流进行了讨论，并分析了任意断面和垂线位置的流场计算公式。在综合各种泥沙动力学研究成果基础之上，探讨了在天然河流中的悬移质输沙能力与沉积条件，分析了河床质起动的控制性因素及推移质输沙方程。提出了受冲淤影响的河床质粒径组成和动态递推公式。结合这些流场与泥沙计算方法及河床形态调整技术，作者提出一个准三维河流动力学模型。该模型只需要河流几何形状、人流条件以及泥沙级配参数，能够模拟出不规则几何形态的河道断面流速分布及平面流场分布，并且对于弯道水流特征与泥沙输送一沉积特征也能得到较好的表现。该模型是对有关河流演变理论和实验成果的综合应用，为研究山区高含沙水流下的河床变形以及洪水演进提供了强有力的工具。  相似文献   

滑坡稳定性判别的非计算方法   总被引：2，自引：6，他引：2  

孔纪名 《山地学报》2001,19(5):446-451

用计算来确定滑坡的稳定性，由于参数选取存不确定因素，就必然导致了其计算结果的不确定性。而滑坡稳定性判别的非计算方法，是通过对滑坡发育程度、形成条件的综合分析来确定滑坡的稳定程度的方法。文中通过归纳分析波坡的形成条件，然后从滑坡地貌条件、动力作用、堆积物特征、诱发因素等方面详细阐述了滑坡稳定性判别的方法，最后，例举了川藏公路102滑坡实例对该方法进行了验证。实践证明该方法是滑坡稳定性中非常实用和有效的方法。  相似文献   

线路平行线间面积计算的统一简捷模型     

李全信 《四川测绘》2001,24(4):172-174

本文根据线路平行线间面积计算的统一模型，分别推证了直线，圆曲和缓和曲线段平行线间面积计算的简捷模型，据此归纳出线路平行线间面积计算的统一简捷模型，它在线路土地征及用建材用料计算等方面都有广泛的应用。  相似文献   

适于多种函模型的测量平差软件     

龚涛  赵国亮 《四川测绘》2001,24(1):32-34

本文给出了平差概括模型以及其它平差函数模型之间的关系，并根据概括平差模型编制了测量平差软件，该软件能完成，间接平差，条件平差，附有参数的条件平差，附有限制条件的间接平差，通过算例，证明该具有一定的实用性。  相似文献   

ON THE EVALUATION OF DEFLECTIONS OF THE VERTICAL USING FFT TECHNIQUE     

HUANG Motao ZHAI Guojun GUAN Zheng OUYANG Yongzhong 《地球空间信息科学学报》2001,4(1):5-13

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Preissmann隐式格式在分汊和环状河道中的应用   总被引：1，自引：0，他引：1       下载免费PDF全文

雷正雄  蒋艳 《水科学进展》2001,12(4):485-490

环状河道在平原地区水系中非常常见,分汊河道也较常见,对这两种河道基于Preissmann格式的水流计算提出了可行的方法。对圣维南方程组进行离散后,用追赶法对各河道进行演算,由水量平衡原理对各结点进行计算,就可求得河道各断面的水流情况。用长江下游江阴至青龙港及杨林段河道的实例进行计算,取得了较为理想的效果。  相似文献   

On the meridional circulation and balance of momentum in the Southern Ocean of POP     

Dirk Olbers  Vladimir O. Ivchenko 《Ocean Dynamics》2001,52(2):79-93

 The circulation of the Southern Ocean is studied in the eddy-resolving model POP (Parallel Ocean Program) by an analysis of zonally integrated balances. The TEM formalism (Transformed Eulerian Mean) is extended to include topography and continental boundaries, thus deviations from a zonally integrated state involve transient and standing eddies. The meridional circulation is presented in terms of the Eulerian, eddy-induced, and residual streamfunctions. It is shown that the splitting of the meridional circulation into Ekman and geostrophic transports and the component induced by subgrid and Reynolds stresses is identical to a particular form of the zonally integrated balance of zonal momentum. In this balance, the eddy-induced streamfunctions represent the interfacial form stresses by transient and standing eddies and the residual streamfunction represents the acceleration of the zonal current by density fluxes in a zonally integrated frame. The latter acceleration term is directly related to the surface flux of density and interior fluxes due to the resolved and unresolved eddies. The eddy-induced circulation is extremely vigorous in POP. In the upper ocean a shallow circulation, reversed in comparison to the Deacon cell and mainly due to standing eddies, appears to the north of Drake Passage latitudes, and in the Drake Passage belt of latitudes a deep-reaching cell is induced by transient eddies. In the resulting residual circulation the Deacon cell is largely cancelled and the residual advection of the zonal mean potential density is balanced by diapycnal eddy and subgrid fluxes which are strong in the upper few hundred meters but small in the ocean interior. The balance of zonal momentum is consistent with other eddy-resolving models; a new aspect is the clear identification of density effects in the zonally integrated balance. We show that the wind stress and the stress induced by the residual circulation drive the eastward current, whereas both eddy species result in a braking. Finally, we extend the Johnson–Bryden model of zonal transport to incorporate all relevant terms from the zonal momentum balance. It is shown that wind stress and induction by the residual circulation carry an eastward transport while bottom form stress and the stress induced by standing eddies yield westward components of transport. Received: 26 June 2001 / Accepted: 2 November 2001  相似文献   

视距测量方法的改进     

范东明 《四川测绘》1996,19(4):171-172

在视距测量中．本文应用上、下视距丝与中丝所夹视角均为17′11″这一原理，证得：上、中、下三丝读数与坚盘读数之间存在着一个多余观测；去除中丝读数同样能求得测站点与碎部点间的平距及高差，且不影响结果的精确性。碎部测量时，对每个碎部点就从根本上减少了一个观测要素。实践证实：此法可节省约15％的碎部测量时间.  相似文献