Automated registration of dense terrestrial laser-scanning point clouds using curves

This paper proposes an automatic method for registering terrestrial laser scans in terms of robustness and accuracy. The proposed method uses spatial curves as matching primitives to overcome the limitations of registration methods based on points, lines, or patches as primitives. These methods often have difficulty finding correspondences between the scanned point clouds of freeform surfaces (e.g., statues, cultural heritage). The proposed method first clusters visually prominent points selected according to their associated geometric curvatures to extract crest lines which describe the shape characteristics of point clouds. Second, a deformation energy model is proposed to measure the shape similarity of these crest lines to select the correct matching-curve pairs. Based on these pairs, good initial orientation parameters can be obtained, resulting in fine registration. Experiments were undertaken to evaluate the robustness and accuracy of the proposed method, demonstrating a reliable and stable solution for accurately registering complex scenes without good initial alignment.     

基于模糊贴近度和改进Prim算法的高光谱图像波段分组排序

传统的基于Prim算法的高光谱图像波段分组排序需要计算所有波段之间的相关系数,并采用满秩相关系数矩阵作为邻接矩阵进行比较,计算复杂度较高。结合模糊数学的相似度衡量理论和高光谱图像的特点,首先提出使用计算简单的最大最小贴近度(maximum and minimum closeness,MMC)作为衡量高光谱图像波段间相关性的参数;然后将MMC的满秩邻接矩阵稀疏化,提取有效波段进行排序,明显降低了排序的波段数目和比较次数。实验结果表明,与传统的Prim算法相比,所提出的算法在保持原有压缩效率的同时,大大降低了波段排序的复杂度,平均波段排序运行时间减少了27%。     

晚新生代西太平洋古海洋环境演化过程与机制

晚新生代西太平洋通过水文循环和碳循环两类关键过程,对区域乃至全球气候变化产生深刻的影响。本文从上新世以来西太暖池及其主流系演化、晚第四纪北太平洋中层水演化和白令海峡开合、第四纪中国东部陆架环境演化以及新生代亚太沉积物源-汇过程与碳埋藏等方面,综述了西太平洋古海洋环境演化过程与机制。上新世以来西太暖池与印尼贯穿流的演化过程伴随构造运动而阶段性地发生,但其在轨道时间尺度上演化的细节过程并不清晰,尚未形成系统性认识。北太平洋中层水以及白令海峡开合等关键高纬过程在冰期旋回中发生了显著变化,并与低纬过程之间存在遥相关。第四纪中国东部陆架环境演化主要受控于海平面变化以及与低纬过程相关联的热量与物质传输,在此背景下,中国东部陆架形成了富有机碳的泥质沉积体系。构造隆升和亚洲季风驱动下的亚洲大陆与邻洋的沉积物源-汇过程具有显著的碳汇效应,可能在大气CO₂浓度（${p_{{\rm{C}}{{\rm{O}}_2}}} $）冰期旋回和新生代气候变冷中发挥重要作用。就西太平洋古海洋环境演化过程与机制中若干关键科学问题开展深入和系统研究,不仅可为建立气候变化的低纬驱动理论提供支撑,也可为更好认识我国陆架环境变化规律以及碳汇潜力提供科学依据。     

基于本体语义的地理信息服务发现

基于本体语义研究地理信息服务发现问题.将加权语义距离和Wu-Palmer法相结合并进行改进计算本体概念语义相似度.引入服务接口依赖关系,提出支持接口多态性的本体语义地理信息服务输入输出匹配方法.最后开发实验原型对基于本体的地理信息服务匹配方法进行实验与分析.     

Combined method of datum transformation between different coordinate systems

The similarity transformation model between different coordinate systems is not accurate enough to describe the discrepancy of them. Therefore, the coordinate transformation from the coordinate frame with poor accuracy to that with high accuracy cannot guarantee a high precision of transformation. In this paper, a combined method of similarity transformation and regressive approximating is presented. The local error accumulation and distortion are taken into consideration and the precision of coordinate system is improved by using the recommended method.     

Development and demonstration of a structured hydrological feature coding system for Europe

Abstract

Validation of large amounts of digital hydrological data and eventual exchange of data between various organisations can benefit from the development of a structured hydrological feature coding system. In this article we describe the development of such a system and present its implementation in the CCM2 structured hydrological feature data set, covering Europe to the Urals and including Turkey. We discuss the coding of river basins, catchments, lakes and rivers. The proposed coding system is largely inspired by the work of Otto Pfafstetter with additions for coding oceans, seas, islands and lakes. Furthermore the coding system can be transferred to features that geometrically intersect the coded hydrological features and we propose some rules on how to establish this transfer.

Citation de Jager, A. L. & Vogt, J. V. (2010) Development and demonstration of a structured hydrological feature coding system for Europe. Hydrol. Sci. J. 55(5), 661–675.     

Comparing expert judgement and numerical criteria for hydrograph evaluation

Abstract

This paper investigates the relationship between expert judgement and numerical criteria when evaluating hydrological model performance by comparing simulated and observed hydrographs. Using a web-based survey, we collected the visual evaluations of 150 experts on a set of high- and low-flow hydrographs. We then compared these answers with results from 60 numerical criteria. Agreement between experts was found to be more frequent in absolute terms (when rating models) than in relative terms (when comparing models), and better for high flows than for low flows. When comparing the set of 150 expert judgements with numerical criteria, we found that most expert judgements were loosely correlated with a numerical criterion, and that the criterion that best reflects expert judgement varies from expert to expert. Overall, we identified two groups of 10 criteria yielding an equivalent match with the expertise of the 150 participants in low and high flows, respectively. A single criterion common to both groups (the Hydrograph Matching Algorithm with mean absolute error) may represent a good indicator for the overall evaluation of models based on hydrographs. We conclude that none of the numerical criteria examined here can fully replace expert judgement when rating hydrographs, and that both relative and absolute evaluations should be based on the judgement of multiple experts.

Editor D. Koutsoyiannis     

Improving the visibility of hydrological sciences from developing countries

Abstract

The increasing level of competition in scientific publishing arguably has a greater negative impact on hydrologists from developing countries and specifically young scientists. This paper discusses the constraints they face and offers suggestions to authors and the hydrological community about how these may be mitigated. These include a lack of access to resources to assist with creating good publications, the difficulty of publishing research based on relatively scarce data, a common problem in many developing countries, and a lack of familiarity with the process of publishing scientific material together with limited access to mentorship from experienced authors. A key point is to ensure that the research question addressed has a broad interest beyond the local study area. However, the more limited hydrological knowledge and the water resources problems of developing countries represent opportunities for internationally relevant research, particularly within the nexus between hydrology and society, or between science and practice. Both of these are high on the international hydrological research agenda.

Editor D. Koutsoyiannis     

Assessment of hydropower potential using spatial technology and SWAT modelling in the Mat River,southern Mizoram,India

Abstract

In this study, a hydrological model and spatial technologies have been employed to assess water availability in the Mat River basin, southern Mizoram, India. Furthermore, the results obtained from the SWAT (Soil and Water Assessment Tool) model, satellite data and GIS tools were utilized to identify the hydropower potential in the basin. Thirty three sites with hydropower potential were identified within 147 km² of the Mat River basin. A total of 3039, 1127 and 805 kW can be harnessed with 50, 75 and 90% dependability, respectively. The study revealed that the hydropower potential of a river basin can be correctly assessed by employing a digital elevation model, stream network data and a hydrological model, such as the SWAT model, within a GIS framework.

Editor D. Koutsoyiannis