Establishing robustness of a spatial dataset in a tolerance‐based vector model

Spatial data are usually described through a vector model in which geometries are represented by a set of coordinates embedded into an Euclidean space. The use of a finite representation, instead of the real numbers theoretically required, causes many robustness problems which are well known in the literature. Such problems are made even worse in a distributed context, where data is exchanged between different systems and several perturbations can be introduced in the data representation. In order to discuss the robustness of a spatial dataset, two implementation models have to be distinguished: the identity and the tolerance model. The robustness of a dataset in the identity model has been widely discussed in the literature and some algorithms of the Snap Rounding (SR) family can be successfully applied in such contexts. Conversely, this problem has been less explored in the tolerance model. The aim of this article is to propose an algorithm inspired by those of the SR family for establishing or restoring the robustness of a vector dataset in the tolerance model. The main ideas are to introduce an additional operation which spreads instead of snapping geometries, in order to preserve the original relation between them, and to use a tolerance region for such an operation instead of a single snapping location. Finally, some experiments on real‐world datasets are presented, confirming how the proposed algorithm can establish the robustness of a dataset.     

基于分布异常的高光谱遥感影像小目标检测算法

提出一种基于分布异常的高光谱遥感影像小目标检测方法。该算法用基于近似相对熵的实码遗传优化投影寻踪方法(RCGOA-PP),有效地将高维数据中隐藏的目标信息集中投影到低维空间中,并用直方图分割的方法提取出小目标。实验证明,此算法精度较高,适用于对高光谱影像中的小目标进行检测。     

北斗GEO/IGSO/MEO卫星定轨地面站构型影响分析及其优化

GNSS卫星定轨精度主要取决于卫星动力学模型精度和GNSS几何观测信息。由于北斗GEO/IGSO卫星静地、高轨特性,以及力学模型不精确等原因,地面几何观测信息对轨道改进至关重要。本文讨论了北斗GEO/IGSO/MEO卫星定轨地面站分布影响及优化改进方法。在简化动力学定轨模型基础上,探讨多历元几何观测信息累积对轨道的改进;研究了北斗导航卫星定轨理想几何构型条件,得到影响定轨精度的几何因子,包括测站数量、覆盖范围、分布密度;利用离散概率密度方法研究地面站构型,分析了3类卫星轨道改进机理和优化方法。通过算例,讨论了增加5个中国区域基准站改善离散概率密度指标,优化全球北斗卫星定轨构型,发现GEO和IGSO卫星精度改善最为明显,MEO卫星改善最小;其中GEO卫星提高了10%,IGSO卫星提高了16%,MEO卫星提高了4%。     

山西天龙山植被及植物资源

采用TWINSPAN对天龙山主要植被进行了分类 ,并用DCA方法分析了植物群落间的生态关系 ,描述了九个主要植物群落类型的特征 ,最后介绍了蕴藏于植被中的天然植物资源的类型及其经济用途 ,提出了植物资源开发利用的对策。     

Foreshore and seabed policy: A Māori perspective

Abstract: The comment provides a Māori perspective on the Foreshore and Seabed Act. In contrast to the western view, Māoris understand their relationship with the coast in ways that are holistic, intertwined and unbounded. The Act disrupts the wairua or spirit of place, impacting on relationships that have been nurtured by whānau and hapū over time.     

Length-weight relationships for six freshwater fish species in Iran

The aim of this study is to report the length-weight relationship parameters (a and b) for some economically important fish species from Iranian freshwaters. The length-weight relationships (LWR) are calculated for six freshwater fish species collected during 2006 and 2007 in Iran. The values of the exponent b in the LWR (W=aLb) vary between 2.985 and 3.543. The LWR with high correlation coefficient (r2) is significant for all the species. These parameters are of great importance to evaluate the relative condition of populations, biology, species management and their fisheries and stock assessment. The application of the length-weight relationships presented here should be limited to the observed length ranges.     

利用球近似大地坐标系统表示变形点位移量的可行性研究

利用站心直角坐标系 (Ne、Ee、Ue)与大地坐标系 (B、L、H )之间的转换关系 ,从理论上证明了利用球近似大地坐标系统所表示的形变量 (Jm、Wm、Gm)与利用监测点的站心直角坐标所表示的形变量 (ΔNe、Δ Ee、ΔUe)的差异不超过总体变形量的 2 / 2 98,并给出了具体的实例加以说明 ,从而得出结论 :在小变形情况下 ,利用球近似大地坐标系统来表示监测点的形变量是可行的。     

Hydrometeorological relationships in a glacierized catchment in the Canadian high arctic

Runoff from a small glacierized catchment in the Canadian high Arctic was monitored throughout one melt season. The stream discharge record is one aspect of a larger project involving glacier mass balance, superimposed ice formation and local climate on a glacier in the Sawtooth Range, Ellesmere Island, Northwest Territories, Canada. To better understand the main factors influencing the production of runoff on the glacier during the period of main summer melt, regression analyses were performed relating daily air temperature, shortwave incoming and net radiation, absorptivity and wind speed to daily glacier discharge. Air temperature at the glacier meteorological station on rain-free days is the element with the greatest correlation with runoff (r² = 0.57; n = 34). A multiple regression of discharge with air temperature, shortwave incoming radiation, net radiation hours and wind speed achieved the best fit (r² = 0.84; n = 34). Rain events (> 10mmd^?1) can dominate daily discharge when they occur during the period of ice melt, creating more runoff per unit area than can be produced by melt alone, and significantly reduce the accuracy of runoff predictions.     

三维拓扑关系的基本问题和研究进展

三维拓扑关系是三维空间关系中最重要的空间关系,是三维空间数据表达、查询、分析与应用的理论基础,是目前拓扑关系研究的热点。本文从三维空间实体的定义和描述、三维拓扑关系描述、表达与应用等方面回顾了国内外学术界所取得的研究进展,同时分析了存在的一些基本问题。     

Salt tectonics vs. inversion tectonics: The anticlines of the western Maestrazgo revisited (eastern Iberian Chain,Spain)

Many works in the last decades underline the role of evaporites, not just as a conditioning factor but as the engine for subsidence and eventually basin inversion. The western Mediterranean alpine ranges are being investigated in this regard because of the presence of discontinuous units of Permian to Triassic evaporites, deposited in the western Tethys basins. This work presents a thorough analysis of two particular structures (Cañada Vellida and Miravete anticlines) in the intraplate Maestrazgo basin (eastern Iberian Chain, Spain) in which evidence to support their reinterpretation as salt-driven structures have been recently reported. Our analysis includes (i) a comprehensive stratigraphic and structural study of the folds along their entire trace, (ii) the compilation of thickness and distribution of evaporite–bearing and supraevaporite units, paying special attention to changes in the thickness of units in relation to anticlines, and (iii) the study of fault patterns, sometimes in relation to the mechanical stratigraphy. All three aspects are also documented and discussed on a regional scale. The new data and interpretations reported here reinforce the extensional origin of the Late Jurassic–Early Cretaceous basins, and the role of regional extensional tectonics as the responsible for the development of first-order syn-sedimentary normal fault zones driving the formation and evolution of sub-basins. These basins were subsequently inverted and deformed, including the formation of complex, box-geometry anticlines that, in their turn, controlled deposition in Cenozoic basins. The review of the arguments that support the alternative of salt tectonics for the origin of such anticlines has allowed us to delve into the sedimentary and tectonic evolution of the inverted extensional basins and to propose a specific model for the development of these faulted anticlines. The role of salt levels and other interlayered detachments in the structuring of sedimentary basins and their inversion is also pondered. The observations in the eastern Iberian Chain reported here have implications to assess ongoing reinterpretations in terms of salt tectonics in other alpine basins and ranges of the western Mediterranean.