Unique identification of vector geographic objects by location and geometry

This article presents a method to uniquely identify vector geographic objects based on their spatial position and geometric characteristics. The method comprises three steps. First, a grid-based spatial indexing (Quadtree grid) is automatically generated according to location, shape and size of the geographic objects. This allows for a simple Quadtree grid generation (the level, row and column number) for every geographic object by three grid parameters (origin, start and end size). Second, a set of algorithms have been developed for extracting geometric characteristics (e.g. representative points, outline and orientation) of geographic objects corresponding to the grid. Third, a strategy for the unique identification of geographic objects is proposed in order to integrate the Quadtree grid and the geometric information. The application of the proposed method is presented in a case study conducted in Jiangsu Province, China. The experiment indicates that this method is more efficient than existing methods at positioning, searching and querying. The unique identifier is also shown to be useful as a technical method to support geographic information systems analytical applications, such as the matching, conflating and sharing of spatial objects.     

An efficient method for rendering linear symbols on 3D terrain using a shader language

With the extensive application of virtual geographic environments and the rapid development of 3D visualization analysis, the rendering of complex vector lines has attracted significant attention. Although there are many rendering algorithms in 3D geographic information system (GIS), they are not sufficiently flexible to meet the requirements for rendering linear symbols composed of diverse colors and shapes. However, the interactive rendering of a scene and the accuracy of the symbols are important components for large-scale, complex vector lines. In this paper, we propose a graphics processing unit (GPU)-accelerated algorithm for rendering linear symbols on 3D terrain. Symbol rendering is embedded within the terrain-rendering process, and vector lines are encoded in a 3D texture and then transferred to the GPU. A set of visual properties are used to enrich the expression of symbols with the help of geometric operations in the fragment shader. A series of experiments demonstrate that the proposed method can be utilized for drawing various pixel-exact linear symbols and can achieve real-time rendering efficiency.     

SEARCHING METHODS FOR RAPID GRID INTERPOLATION*

A widely used method for grid interpretation from a set of discrete sample points is based on the inverse distanceweighted model. This method requires the identification of k-nearest sample points for each grid point, probably the most time-consuming portion of the grid interpolation process. Three searching methods for identifying the k-nearest sample points are discussed and compared. Two of these methods were consistenty faster without sacrificing accuracy than the brute-force searching method, and one method was from one to over 90 times faster than the brute-force searching method.     

水系的分形维数及其含义

在分述水系分维数的几个计算方法基础上，对两上试区采用地图照相缩小后扫描以及图象处理的方法提取河流信息，以计盒方法计算水系的分维数，并据此提出划以域地貌侵蚀发育阶段的方法。     

GIS and geometric representation in facility location problems

Abstract

A neglected aspect of facility location problems is the geometric representation of the facilities sited and clients served. Point objects represent these entities in most facility location problems. This can cause solution error and limit the range of potential solutions. The increasing capabilities of geographical information systems (GIS) to represent, store and manipulate spatial entities provides a substantial but unrealized potential for more sophisticated geometric representation in facility location problems. This paper provides a framework for realizing this potential. Specifically, this paper: (i) synthesizes existing formulations; (ii) develops a unified mathematical framework; (iii) identifies feasible computational strategies that can be implemented within a GIS framework, and; (iv) discusses potential GIS-based solution algorithms.     

A tile-based method for geodesic buffer generation in a virtual globe

Geometric buffers are important for spatial analysis in many applications of geographic information systems (GISs), such as environmental measurement and management, human health, urban planning, etc. Geometric buffer generation algorithms are well studied in the Euclidean space where the buffer distance is measured by Euclidean metrics; however, very few algorithms are available for generating geometric buffers on the terrain surface in a virtual globe where the buffer distance is measured by geodesic metrics. This paper proposes a tile-based method for geodesic buffer generation according to the characteristics of a virtual globe. It extends the vector tile model (VTM) to organize terrain and vector data, and the XYH algorithm is improved to build geodesic distance fields for terrain meshes. Based on the data organization and the improved XYH algorithm, a geodesic buffer is generated via three main steps: selecting and assembling tiles, updating geodesic distance fields and tracing the boundaries of buffer zones. This method is implemented with multi-scale terrain and vector data, and the experimental results show that it is valid and exact and can be applied in practical applications.     

地面高精度磁测在西藏恰功铁矿勘查中的应用效果

恰功铁矿是近几年新发现的矿山,然而矿体的形态、大小、埋深、位置、产状、边界等几何特征还没有被认识清楚。为了弄清这些问题,本文通过欧拉反褶积方法对磁异常化极数据进行了反演,反演矿体深度为0-120m;在C-6异常中心选择了两条剖面进行了2.5维拟合反演,反演矿体厚度为20~30m,欧拉反褶积反演结果和2.5维拟合反演结果与ZK32钻孔验证结果相吻合。最后,通过建立恰功矽卡岩型铁矿地质—地球物理找矿模型,为该地区寻找隐伏夕卡岩型铁矿提供了思路。     

Comparative evaluation and analysis of online geocoding services

Geocoding is an uncertain process that associates an address or a place name with geographic coordinates. Traditionally, geocoding is performed locally on a stand-alone computer with the geocoding tools usually bundled in GIS software packages. The use of such tools requires skillful operators who know about the issues of geocoding, that is, reference databases and complicated geocoding interpolation techniques. These days, with the advancement in the Internet and Web services technologies, online geocoding provides its functionality to the Internet users with ease; thus, they are often unaware of such issues. With an increasing number of online geocoding services, which differ in their reference databases, the geocoding algorithms, and the strategy for dealing with inputs and outputs, it is crucial for the service requestors to realize the quality of the geocoded results of each service before choosing one for their applications. This is primarily because any errors associated with the geocoded addresses will be propagated to subsequent decisions, activities, modeling, and analysis. This article examines the quality of five online geocoding services: Geocoder.us, Google, MapPoint, MapQuest, and Yahoo!. The quality of each geocoding service is evaluated with three metrics: match rate, positional accuracy, and similarity. A set of addresses from the US Environmental Protection Agency (EPA) database were used as a baseline. The results were statistically analyzed with respect to different location characteristics. The outcome of this study reveals the differences among the online geocoding services on the quality of their geocoding results and it can be used as a general guideline for selecting a suitable service that matches an application's needs.     

A GIS method to aid in non-point source critical area analysis

Abstract

The use of remote sensing techniques, image processing, computer mapping and overlays to make inventories of land use and to improve land and water management has increasing potential. Advantages of these techniques include greater geometric resolution and potential time and money savings. The increasing capabilities of personal computers and workstations (hardware and software) and the greater availability of databases have simplified the application of these techniques. In this application, a geographical information system (GIS) was used to facilitate the identification of critical non-point source areas of pollution by sediment-related nutrients. This critical source area information might then be used to aid in the development of non-point source control strategies or for monitoring programme design. This study shows the potential of using GIS in selecting critical source areas for sediment-related water quality problems and land resource protection.     

数字高程模型在活动断层位置及地表变形变位特征提取研究中的应用

活动断层的位置分布及其地表变形变位特征的准确识别是研究和评价活动断层的基础,国内外学者利用数字高程模型(DEM)对断层提取进行了大量研究。本文基于DEM的活动断层位置的提取方法进行综述,总结了DEM提取断层位置的地貌形态特征分析、图像处理以及综合处理提取方法,突出介绍了高分辨率DEM在详细的断层位置分布提取中的优势,DEM在断层地表变形变位及其特征参数提取研究中的最新应用进展。随着高分辨率DEM的快速发展,DEM及其空间分析技术已成为一种常见的地学研究方法,将其与野外调查、遥感、测年等技术结合进行综合分析,能够促进对活动断层的深入研究,并成为断层定量化研究强有力的技术手段。     

A commentary on GeoVRML: a tool for 3D representation of georeferenced data on the web

GeoVRML techniques have the potential to provide functional and transparent communication between geographical information and 3D Web visualization tools. This report outlines recommended practices and modifications to the VRML97 standard to consider pre-existing cartographic projections and georeferenced data. The concepts outlined for incorporating georeferenced coordinate systems in VRML worlds have generic applicability to 3D Web technologies like MPEG-4, Java3D and Chrome.     

Spatial subdivision of complex indoor environments for 3D indoor navigation

As we realize that we spend most of our time in increasingly complex indoor environments, applications to assist indoor activities (e.g. guidance) have gained a lot of attention in the recent years. The advances in ubiquitous computing made possible the development of several spatial models intending to support context-aware and fine-grained indoor navigation systems. However, the available models often rely on simplified representations (e.g. 2D plans) and ignore the indoor features (e.g. furniture), thereby missing to reflect the complexity of the indoor environment. In this paper, we introduce the Flexible Space Subdivision framework (FSS) that allows to automatically identify the spaces that can be used for indoor navigation purpose. We propose a classification of indoor objects based on their ability to autonomously change location and we define a spatial subdivision of the indoor environment based on the classified objects and their functions. The framework can consider any 3D indoor configuration, the static and dynamic activities it hosts and it enables the possibility to consider all types of locomotion (e.g. walking, flying, etc.). It relies on input 3D models with geometric, semantic and topological information and identifies a set of subspaces with dedicated properties. We assess the framework against criteria defined in previous researches and we provide an example.     

Topological approach to remote sensing

Summary. The topological problem underlying remote sensing is analysed by determining the geometric singularities that an unknown surface or structure generically impresses on a sensing wavefield. It is shown that the analytical singularities observed in scattering amplitudes and echograms are produced by the topological singularities of the scattering system. Imposing the principle of structural stability on the inverse scattering problem, the singularities that generically occur in recorded signals, travel-time curves, surface contour maps and Fresnel-zone topographies can, together with the associated high-intensity diffraction patterns, be classified into a few universal standard forms described by catastrophe polynomials. As the source-receiver positions vary, the patterns change their morphologies in terms of specific bifurcation sets. By applying singularity and bifurcation theory to allow the effects of caustics (both in ray and wave theory) to be incorporated into three-dimensional techniques for reconstructing surfaces and subsurface structures from their echoes, the interpretation process is considerably simplified and permits an on-site 3D survey. Universal power laws for singularity-dominated echo amplitude variations with the source frequency are deduced. The shape of a scattering surface is reconstructed using the high-frequency regime alone. Discontinuities in the surface, edges and faults, are discussed in terms of constraint catastrophes and the patterns they produce in echograms are classified.     

大规模地形实时绘制算法

该文提出一种适合大规模地形实时绘制的简单高效的LOD简化算法。该算法使用一种紧凑有效的规则网格表示方法,优化网格节点的数目,减少可视化过程中的计算量,降低额外内存开销。探讨该算法相关的数据组织、视域裁剪、LOD层次选择、裂缝消除、三角形化等关键问题。实验结果表明,该算法实现简单,内存开销较少,CPU耗费小,对图形卡要求低,能够在普通机器上实现大规模地形的实时漫游。     

新型冠状病毒肺炎疫情公众关注度的时空差异与影响因素

公众关注作为疫情防控与舆情治理的重要环节,其时空差异与影响因素却鲜见被讨论。因此,文章将百度搜索指数作为网络公众关注度的测量指标,采用百度人口流动大数据和疫情实时监测数据,运用空间分析、时空可视化、回归分析等方法,分析2020-01-09—03-02中国公众对“新型冠状病毒”网络关注度的省域时空差异与影响因素。研究发现：1）在空间上,公众对疫情的关注度东、西部差异较大,沿海高于内陆,且与疫情高发区吻合;在时间上,武汉“封城”前后各省份的公众关注度分布格局基本趋于一致,且“封城”后均明显高于“封城”前;春节期间关注度达到最高峰,而后随疫情周期性规律（潜伏—暴发）呈波动式下降;关注主题遵循“从早期对相关病毒的搜索到后期关注临床诊断与发展状况”的疫情发展规律。2）疫情动态数据、武汉人口流动的日动态因素与固定区位特征的经济社会发展因素会不同程度地影响受众对疫情的关注度,当疫情基本得到控制,宏观区位因素对公众关注度的影响作用开始凸显,具有持续稳定的影响;3）影响因素在疫情暴发前后2个阶段对公众关注度起着不同的影响效果。在疫情暴发初期,公众更易受疫情动态信息影响引发主动搜索行为;而在疫情暴发后期阶段,公众将注意力转移到流入各省份的武汉人口上。     

GENETIC ALGORITHMS AS A STRATEGY FOR FEATURE SELECTION

Genetic algorithms have been created as an optimization strategy to be used especially when complexresponse surfaces do not allow the use of better-known methods (simplex, experimental designtechniques, etc.). This paper shows that these algorithms, conveniently modified, can also be a valuabletool in solving the feature selection problem. The subsets of variables selected by genetic algorithms aregenerally more efficient than those obtained by classical methods of feature selection, since they canproduce a better result by using a lower number of features.     

Stochastic behaviour and scaling laws in geoelectrical signals measured in a seismic area of southern Italy

We explore the inner dynamics of daily geoelectrical time series measured in a seismic area of the southern Apennine chain (southern Italy). Autoregressive models and the Higuchi fractal method are applied to extract maximum quantitative information about the time dynamics from these geoelectrical signals. First, the predictability of the geoelectrical measurements is investigated using autoregressive models. The procedure is based on two forecasting approaches: the global and the local autoregressive approximations. The first views the data as a realization of a linear stochastic process, whereas the second considers the data points as a realization of a deterministic process, which may be non-linear. Comparison of the predictive skills of the two techniques allows discrimination between low-dimensional chaos and stochastic dynamics. Our findings suggest that the physical systems governing electrical phenomena are characterized by a very large number of degrees of freedom and can be described only with statistical laws. Second, we investigate the stochastic properties of the same geoelectrical signals, searching for scaling laws in the power spectrum. The spectrum fits a power law P (  f )∝  f  ^−α , with the scaling exponent α a typical fingerprint of fractional Brownian processes. In this analysis we apply the Higuchi method, which gives a linear relationship between the fractal dimension D _Σ and the spectral power law scaling index α : D _Σ=(3− α )/2. This analysis highlights the stochastic nature of geoelectrical signals recorded in this seismic area of southern Italy.     

Fast Nearest Neighbor Classification Methods for Multispectral Imagery

Nearest neighbor classifiers have not been widely used by remote sensing practitioners. The lack of acceptance of these classifiers may be partially due to their notoriously slow speed of execution which makes them impractical for the classification of mega-pixel images. However, training data reduction, distance measure optimization, and neighbor searching algorithms based on the modified k-d tree can speed nearest neighbor classification substantially.     

摄影测量三维重建中多源信息融合方法探讨

分析摄影测量三维重建中不同数据源的特点,针对现有多源数据融合存在的有限数据源低层次融合问题,提出一种基于影像特征、GIS信息和3D TIN模型融合的层次结构与算法流程 .该算法主要包括多边形区域增长、几何推理和建筑物几何模型平差等处理,为基于摄影测 量的三维城市模型自动重建提供了一种新的思路与方法.     

A hybrid representation for modeling,interactive editing,and real-time visualization of terrains with volumetric features

Terrain rendering is a crucial part of many real-time applications. The easiest way to process and visualize terrain data in real time is to constrain the terrain model in several ways. This decreases the amount of data to be processed and the amount of processing power needed, but at the cost of expressivity and the ability to create complex terrains. The most popular terrain representation is a regular 2D grid, where the vertices are displaced in a third dimension by a displacement map, called a heightmap. This is the simplest way to represent terrain, and although it allows fast processing, it cannot model terrains with volumetric features. Volumetric approaches sample the 3D space by subdividing it into a 3D grid and represent the terrain as occupied voxels. They can represent volumetric features but they require computationally intensive algorithms for rendering, and their memory requirements are high. We propose a novel representation that combines the voxel and heightmap approaches, and is expressive enough to allow creating terrains with caves, overhangs, cliffs, and arches, and efficient enough to allow terrain editing, deformations, and rendering in real time.