封闭曲线裁剪算法在矢量地图显示中的应用     

安添琳 《东北测绘》2012,(8):170-172

在参考经典Sutherland-Hodgeman裁剪算法的基础上,实现了封闭曲线裁剪算法,使得裁剪结果成为原被裁剪封闭曲线的局部线段。本算法应用在2维矢量地图缩放显示中,通过矩形裁剪窗口裁剪矢量图并显示,从而提高整幅矢量图的显示速度。实验表明,该新算法能够简单、高效、准确地裁剪出理想的线段,并在很大程度上提高2维矢量图的显示速度。  相似文献   

CPⅢ高程网最小独立闭合环的一种搜索算法     

李建平  明祖涛  张届  游振兴 《地理空间信息》2012,10(6):150-153,1,16

水准测量结束后,对观测成果进行往返较差、附合路线及闭合环的闭合差检查是必不可少的工作。CPⅢ高程控制网网形独特,它部分边含有往返测或双次观测且属于大型控制网(观测边可能含有数千条)。根据最小独立闭合环及最小独立附合路线的限制条件,依据CPⅢ高程控制网的特点,利用Dijkstra算法思想,提出了最小路径搜索法并进行编程实现,通过算例验证了其正确性和高效性。  相似文献   

日本富山县中田浦滑坡滑带内的黄铁矿   总被引：6，自引：0，他引：6  

郑国东  徐胜  郎煜华  段毅 《地球化学》2006,35(2):201-210

日本富山县境内的中田浦滑坡剖面中产出以立方体为主要晶形的微小黄铁矿颗粒,它们多沿滑带土中的细裂缝分布。黄铁矿的产出状况、晶体形态以及滑带土的岩矿和地球化学特征均显示这些黄铁矿是滑带岩石粘土化作用过程的伴生产物,揭示滑带内的还原性氧化还原条件,它们总体受滑带的发生和发展所控制。因此,滑带土中的次生黄铁矿对于滑带土的形成具有特别的指相意义,有可能作为备选指标用来判断滑带的产生历史和发展进程,从而估计滑坡的发展演化。  相似文献   

毗邻建筑考虑局部场地效应时的LQG控制     

于骁  张文首  林家浩 《地震工程与工程振动》2007,27(6):197-202

本文基于虚拟激励法和留数定理推导出毗邻建筑考虑局部场地效应时在平稳随机地震激励下的LQG控制问题的闭合解。利用此闭合解进行场地土参数研究表明,场地土参数对位移和加速度响应的影响是不同的,甚至是相反的。因此对于给定的LQG控制加权阵Q和R,场地土的卓越频率和阻尼比变化对减震效果有显著影响,应予以重视。  相似文献   

以坐标差为因子的导线平差     

袁江红 《上海国土资源》2007,(4):48-51

根据全站仪可以直接测量导线坐标的特点,以基本的测量平差知识为基础,探讨了以测量所得的坐标差为观测因子来建立平差函数模型,并依据间接平差原理进行平差的方法。平差结果和传统的平差方法的结果进行了比较,得出了这种平差方法的可行性。  相似文献   

Power and robustness of Aitchison's test for complete subcompositional independence in closed arrays     

Alex Woronow 《Mathematical Geology》1986,18(6):563-575

This paper examines some aspects of the power and robustness of the test for complete subcompositional independence proposed by Aitchison (1982). Although the computed test statistics commonly do not approach being ² distributed throughout their range, the upper tail of their distribution does mimic the ² distribution sufficiently to yield a quite robust test when variates are drawn from identical distributions with different distribution parameters or even when variates are drawn from different distributions. But the magnitude of correlations among the variables and the proportion of correlated to independent variables that compose the closed data vectors affect the power of the test.  相似文献   

Effect of various transformations on the analysis of percentage data     

J. C. Butler 《Mathematical Geology》1981,13(1):53-68

Proper analysis of transformed data arrays (such as percentages) requires paying special attention to the effects of the transformation process itself. Effects of several commonly used transformations (including percentage formation, row and column normalization, and the square root transformation) have been examined with emphasis placed on changes in the statistical and geometrical properties of column vectors that accompany the application of the transformation. Even though many transformations, including taking the square root, open up the percentage array, this does not allow one to ignore the fact that percentage formation may have considerably modified the statistical and geometrical properties of the columns of the matrix. In preparing to analyze percentages one should give serious consideration to using the row normalized form of the data matrix. The individual elements in such a matrix are the direction cosines of the vector in M-dimensional space, the row vectors are of unit length, and the row normalized matrix computed from the closed array is equal to the row normalized, open matrix that is unobservable. Application of a column transformation (such as range restriction and proportion of the maximum) destroys the equality of the open and percentage row normalized matrices. Despite repeated claims to the contrary, one can not deduce the statistical and geometrical properties of the open matrix given only the statistical and geometrical properties of the closed matrix.  相似文献   

Sedimentological and palaeohydrological responses to tectonics and climate in a small, closed, lacustrine system: Oligocene As Pontes Basin (Spain)   总被引：1，自引：0，他引：1  

A. Sáez  L. Cabrera 《Sedimentology》2002,49(5):1073-1094

ABSTRACT A small, closed, lacustrine system developed during the restraining overstep stages of the Oligocene As Pontes strike‐slip basin (Spain). The increase in basin accommodation and the headward spread of the drainage, which increased the water input, triggered a change from shallow, holomictic to deeper, meromictic conditions. The lower, shallow, lacustrine assemblage consists of mudstone–carbonate cycles recording lacustrine–palustrine ramp deposition in a saline lake. High Sr content in some early diagenetic calcites suggests that aragonite and calcite made up the primary carbonate muds. Early dolomitization took place together with widespread pedogenic activity. The upper, deep, freshwater, lacustrine assemblage includes bundles of carbonate–clay rhythmites and fine‐grained turbidite beds. Primary calcite and diagenetic siderite make up the carbonate laminae. The Mg content of the primary carbonates records variations in Mg/Ca ratios in lacustrine waters. δ¹⁸O and δ¹³C covariance trends in calcite reinforce closed drainage conditions. δ¹⁸O data indicate that the lake system changed rapidly from short‐lived isotopically light periods (i.e. from seasonal to pluriannual) to longer steady‐state periods of heavier δ¹⁸O (i.e. from pluriannual to millennial). The small δ¹³C changes in the covariant trends were caused by dilute inflow, changing the contributions of dissolved organic carbon in the system and/or internal variations in lacustrine organic productivity and recycling. In both shallow and deep carbonate facies, sulphate reduction and methanogenesis may account, respectively, for the larger negative and positive δ¹³C shifts recorded in the early diagenetic carbonates (calcite, dolomite and siderite). The lacustrine system was very susceptible to high‐frequency, climatically forced water balance variations. These climatic oscillations interfered with the low‐frequency tectonic and morphological changes in the basin catchment. This resulted in the superposition of high‐order depositional, mineralogical and geochemical cycles and rhythms on the lower order lacustrine infill sequence.  相似文献   

Sedimentation in a fluvially infilling, barrier-bound estuary on a wave-dominated, microtidal coast: the Ouémé River estuary, Benin, west Africa     

Edward J. Anthony  Lucien M. Oyéd醠 Jacques Lang‡ 《Sedimentology》2002,49(5):1095-1112

The Ouémé River estuary is located on the seasonally humid tropical coast of Benin, west Africa. A striking feature of this microtidal estuary is the presence of a large sand barrier bounding a 120 km² circular central basin, Lake Nokoué, that is being infilled by heterogeneous fluvial deposits supplied by a relatively large catchment (50 000 km²). Borehole cores from the lower estuary show basal Pleistocene lowstand alluvial sediments overlain by Holocene transgressive–highstand lagoonal mud and by transgressive to probably early highstand tidal inlet and flood‐tidal delta sand deposited in association with non‐preserved transgressive sand barriers. The change in estuary‐mouth sedimentation from a transgressive barrier‐inlet system to a regressive highstand barrier reflects regional modifications in marine sand supply and in the cross‐barrier tidal flux associated with barrier‐inlet systems. As barrier formation west of the Ouémé River led to an increasingly rectilinear shoreline, the longshore drift cell matured, ensuring voluminous eastward transport of sand from the Volta Delta in Ghana, the major purveyor of sand, to the Ouémé embayment, 200 km east. Concomitantly, the number of tidal inlets, and the tidal flux associated with a hitherto interlinked lagoonal system on this coast, diminished. Complete sealing of Lake Nokoué has produced a large, permanently closed estuary, where tidal intrusion is assured through the interconnected coastal lagoon via an inlet located 60 km east. Since 1885, tides have entered the estuary directly through an artificial outlet cut across the sand barrier. Although precluding the seaward loss of fluvial sediments, permanent estuary‐mouth closure has especially deprived the highstand estuary of marine sand, a potentially important component in estuarine infill on wave‐dominated coasts. In spite of a significant fluvial sediment supply, estuarine infill has been moderate, because of the size of the central basin. Estuarine closure has resulted in two co‐existing highstand sediment suites, with limited admixture, the marine‐derived, estuary‐mouth barrier and upland‐derived back‐barrier sediments. This situation differs from that of mature barrier estuaries characterized by active fluvial‐marine sediment mixing and facies interfingering.  相似文献   

Compositional Kriging: A Spatial Interpolation Method for Compositional Data   总被引：3，自引：0，他引：3  

Dennis J. J. Walvoort  Jaap J. de Gruijter 《Mathematical Geology》2001,33(8):951-966

Compositional data are very common in the earth sciences. Nevertheless, little attention has been paid to the spatial interpolation of these data sets. Most interpolators do not necessarily satisfy the constant sum and nonnegativity constraints of compositional data, nor take spatial structure into account. Therefore, compositional kriging is introduced as a straightforward extension of ordinary kriging that complies with these constraints. In two case studies, the performance of compositional kriging is compared with that of the additive logratio-transform. In the first case study, compositional kriging yielded significantly more accurate predictions than the additive logratio-transform, while in the second case study the performances were comparable.  相似文献