Parallel polygon line shading: the quest for more computational power from an existing GIS algorithm

Abstract

Utilising the powerful resources of a parallel computer has become a technique available to the GIS software engineer for increasing the performance of such complex software systems. This paper discusses the effectiveness of both automatic and manual parallelising techniques with a view to making an assessment as to whether the inherent sequential structure of GIS software is a detrimental factor inhibiting the use of such techniques. With the aid of the Scan Line Fill (SLF) algorithm in GIMMS, it has been shown that whilst automated parallelization has no merits in this case, a significant performance benefit can be achieved with algorithm redesign at the macro level to exploit the natural geometric parallelism inherent within the algorithm. However, the results illustrate that the full potential of this approach will not be appreciated until the I/O bottleneck is completely overcome, as opposed to merely avoided.     

Actor-networks and implementation: examples from conservation GIS in Ecuador

Recommendations for implementation and evaluation of Geographical Information Systems (GIS) can benfit from a broader theoretical foundation to support investigation, understanding and improvement. This paper discusses Actor-Network Theory (ANT) as a framework to delineate and evaluate the social and technical interactions involved in GIS implementation. The proposed process traces actor-network interactions through texts, technical objects, people, money and control. Actor alignment, actor-network stability and obligatory points of passage are evaluated to compare actor-networks. Case study research on conservation GIS implementation in Ecuador illustrates these methods. The strength of these actor-networks is examined through analysis of actors' interactions and the presence and function of an obligatory point of passage. Stronger actor-networks exhibit alignment among actors, co-location of an obligatory point of passage with the center of calculation and credit sharing.     

An algorithm for converting weather radar data into GIS polygons and its application in severe weather warning systems

An algorithm was developed for converting radar data from matrix format into polygons that can be easily visualized, processed, and analyzed using Geographic Information Systems. Spatial operators can be used to overlap radar polygons with land surface features represented by points, lines, and polygons to meet the demands of severe weather identification and tracking and risk recognition. Application and testing of the algorithm demonstrate that the converted radar polygons are suitable for use in weather modification, risk assessments of flash floods in urban areas, and the identification of lightning activity for lightning risk recognition, all of which are essential in real-time severe weather monitoring and warning.     

A cell-based algorithm for evaluating directional distances in GIS

Directional distance is commonly used in geographical information systems as a measure of openness. In previous works, the sweep line method and the interval tree method have been employed to evaluate the directional distances on vector maps. Both methods require rotating original maps and study points in every direction of interest. In this article, we propose a cell-based algorithm that pre-processes a map only once; that is, it subdivides the map into a group of uniform-sized cells and records each borderline of the map into the cells traversed by its corresponding line segment. Based on the pre-processing result, the neighbouring borderlines of a study point can be directly obtained through the neighbouring cells of the point, and the borderlines in a definite direction can be simply acquired through the cells traversed by the half line as well. As a result, the processing step does not need to enumerate all the borderlines of the map when determining whether a point is on a borderline or finding the nearest intersection between a half line and the borderlines. Furthermore, we implement the algorithm for determining fetch length in coastal environment. Once the pre-processing is done, the algorithm can work in a complex archipelago environment such as to calculate the fetch lengths in multiple directions, to determine the inclusion property of a point, and to deal with the singularity of a study point on a borderline.     

A genetic algorithm for designing optimal patch configurations in GIS

Optimal patch design is a generic problem in which the objective is to find the best configuration of patches subject to multiple criteria. It is a hard problem in spatial geometry relevant to numerous applications in spatial planning and analysis. GIS packages do not have optimal patch design functions and there has been very little research in this area. This paper describes a computer system for solving optimal patch design problems in raster GIS. The method uses a genetic algorithm search heuristic combined with a region-growing programme that generates alternative patch configurations. The version described here solves multiple patch problems and was developed from an earlier version for designing single patches. In tests on a hypothetical planning problem the multi-patch version was found to be more efficient, but less effective, than the single patch version. The last part of the paper discusses outstanding issues regarding the applicability usability and external validity of the system and suggests ideas for further research.     

Split-Match-Aggregate (SMA) algorithm: integrating sidewalk data with transportation network data in GIS

Sidewalk geodata are essential to understand walking behavior. However, such geodata are scarce, only available at the local jurisdiction and not at the regional level. If they exist, the data are stored in geometric representational formats without network characteristics such as sidewalk connectivity and completeness. This article presents the Split-Match-Aggregate (SMA) algorithm, which automatically conflates sidewalk information from secondary geometric sidewalk data to existing street network data. The algorithm uses three parameters to determine geometric relationships between sidewalk and street segments: the distance between streets and sidewalk segments; the angle between sidewalk and street segments; and the difference between the lengths of matched sidewalk and street segments. The SMA algorithm was applied in urban King County, WA, to 13 jurisdictions’ secondary sidewalk geodata. Parameter values were determined based on agreement rates between results obtained from 72 pre-specified parameter combinations and those of a trained geographic information systems (GIS) analyst using a randomly selected 5% of the 79,928 street segments as a parameter-development sample. The algorithm performed best when the distances between sidewalk and street segments were 12 m or less, their angles were 25° or less, and the tolerance was set to 18 m, showing an excellent agreement rate of 96.5%. The SMA algorithm was applied to classify sidewalks in the entire study area and it successfully updated sidewalk coverage information on the existing regional-level street network data. The algorithm can be applied for conflating attributes between associated, but geometrically misaligned line data sets in GIS.     

定性GIS在时空间行为研究中的应用

定性GIS已经成为地理学混合研究方法的重要组成部分,通过扎根理论并与可视化结合、GIS和民族志整合等途径,对时空间行为研究产生了深远的影响。其通过文本或非文本质性材料与GIS地理特征的整合,形成了时空行为研究中独特的地理环境系统与空间机制分析,一个重要的前沿领域就是地理叙事在时间地理学研究中的应用。时间地理学是研究人类时空行为的重要视角,但由于对个体主观性及行为的社会文化因素的相对忽视等原因,受到了一定的质疑。近年来以GIS为代表的地理空间技术的定性分析与表达,为时间地理学融入质性分析提供了方法论基础。关美宝创建的基于GIS的地理叙事方法,通过借鉴叙事分析的一般方法尤其是三维叙事空间分析,结合时间地理学概念框架,开发了基于GIS平台的计算机辅助叙事分析组件(3D-VQGIS),实现了在GIS内可视化的、循环交互的叙事分析,为定性GIS发展中GIS与叙事分析方法的融合做出了贡献。将地理叙事方法用于时空行为研究,可以为时间地理学方法创造一个更便于理解与解释研究对象日常行为的地理环境,为其融入行为与主体的质性分析提供从数据整合、数据分析到解释与展示的一整套研究方法与具体操作工具。     

定性地理信息系统在城市社会空间研究中的应用

定性地理信息系统(定性GIS)是西方人文地理学定性研究的重要方法。它集成了定性和空间元素,更全面地阐明空间背景是如何被社会建构的。这种多元要素的整合,可以表达人们生活空间的多样性和复杂性,有助于展示生活路径的三维可视化细节,实现可视化社会空间过程。本文试图梳理西方定性GIS的方法论并探讨其在基于情感表达的个体数据采集分析、基于混合方法的可视化活动空间研究以及基于多重互动视角的社会空间研究中的应用。定性GIS包含微观和宏观层面的多重含义,使得研究者可以从多个有利位置观察问题并参与其中,有助于城市社会空间研究理论创新,为社会空间研究提供可探索空间。最后,从学科建设、方法论拓展、研究成果表达和研究议题选择等方面对中国开展同类研究进行展望。     

GIS research to address tensions in geography

The rise of Geographic Information Systems (GIS) technologies has been producing powerful tools for spatial data processing, management, analysis, modeling, and visualization. While supporting many tasks, GIS technologies have evoked new thinking and advanced intellectual inquiries in geography. Technological advances in other fields often stimulate new research questions and lead to revolutionary discoveries. The Hubble telescope revolutionizes our understanding of the universe, and 3D digital microscopes transform our knowledge of the coordination among biological, neurological, and physiological systems in living organisms. Can GIS claim similar revolutionary effects on geography? The answer is much up for debate. With GIS technologies, geographic studies can explore a broader extent across multiple scales in space and time and tackle problems through increasingly complex spatial statistics, visual analytics, computation, simulation, machine learning, and artificial intelligence. Both the Hubble telescope and 3D digital microscope were built based on scientific research that subserves the technological advances for inquiries into space and life systems. Likewise, GIScience research innovates GIS methods that enable novel geographic investigations and therefore contribute to geographic knowledge production. For the sake of simplicity, the term GIS used here represents both GIScience and GIS technologies. This essay attempts to clarify the intellectual contributions of GIS to geography on the following two questions: (1) What novel geographic thinking is driven by GIS? (2) How may GIS provoke new geographic inquiries and knowledge? Building on Nystuen's notion of four tensions that trigger geographic questions, the essay discusses how GIS innovations mediate historical tension, space‐time tension, dimensional tension and scale tensions.     

A preliminary application GIS in glaciological research along the traverse route from Zhongshan Station to Dome A, Antarctica

GIS is applied in glaciological research along the traverse route from Zhongshan Station to Dome A, one of the key routes in ITASE project, to display, process, manage and analyze the data obtained mainly by the 3rd Chinese Inland Expedition, together with Antarctic databases provided by ADD and BEDMAP project. The ways of ADD data merging and clipping, and coordinate projection transformation of field data and BEDMAP data are introduced. Elevation data derived by GPS navigator are corrected using ADD and ArcView's contour interpolation. Sub ice topography and ice thickness along the route are extracted from BEDMAP database. Slope and aspect data are derived at each positioning station. GIS is a convenient and useful tool for us to record, query and display a variety of data in detail along the traverse route.     

遥感与GIS在东亚飞蝗灾害研究中的应用

蝗灾属于毁灭性的生物灾害,它和水灾、旱灾一起构成人类社会的三大自然灾害,一旦爆发,对国家粮食安全、农民增收、社会安定可造成严重的影响。将遥感与GIS结合,对蝗虫生境特征、历史蝗灾记录、蝗害发生时有关数据进行集成和分析,可提供蝗灾时空变化、蝗灾范围、蝗灾程度、灭蝗的最佳时段等重要信息。本文重点论述遥感与GIS在蝗灾中的应用,以遥感反演的温度和水分为例来讨论蝗灾前后生境的变化状况,依靠遥感等高新技术实现飞蝗灾害监测的信息化。信息化监测与防蝗站观测相结合的方法已经成为监测蝗灾发生的最有效途径     

A polygon reduction algorithm for enhancing graphics performance with application to fast rendering of geophysical and ionospheric model data

Many scientific applications employ computer graphics as a means of interactively visualizing two-dimensional geophysical data sets. This paper presents an algorithm for improving rendering performance by using an image segmentation approach to reduce the number of rendered polygons while maintaining complete display fidelity. Though applied here specifically to the output from a numerical ionosphere model, the algorithm is broadly applicable to many other two-dimensional cellular data sets, geophysical and otherwise. In an ionospheric context, this algorithm demonstrates the ability to reduce the number of rendered polygons by 95 per cent or more with a corresponding reduction in rendering time.     

Fusing remote sensing with sparse demographic data for synthetic population generation: an algorithm and application to rural Afghanistan

We develop a new algorithm for population synthesis that fuses remote-sensing data with partial and sparse demographic surveys. The algorithm addresses non-binding constraints and complex sampling designs by translating population synthesis into a computationally efficient procedure for constrained network growth. As a case, we synthesize the rural population of Afghanistan, validate the algorithm with in-sample and out-of-sample tests, examine the variability of algorithm outputs over k-nearest neighbor manifolds, and show the responsiveness of our algorithm to additional data as a constraint on marginal population counts.     

Incorporating fuzzy set methodologies in a DBMS repository for the application domain of GIS

It has been recently recognized that fuzzy set theory provides useful concepts and tools for both the representation and analysis of the uncertainty related to geographical data. Hence the incorporation of fuzzy set methodologies into a DBMS repository for the application domain of GIS should be beneficial and will improve its level of intelligence. Focusing in this area the paper addresses both a representation and a reasoning issue. Specifically, it extends a general spatial data model to deal with the uncertainty of geographical entities, and shows how the standard data interpretation operations available in GIS packages may be extended to support the fuzzy spatial reasoning. Representative geographical operations, suchas the fuzzy overlay, fuzzy distance and fuzzy select, are examined, while several real world examples are given.     

Fuzzy information representation and processing in conventional GIS software: database design and application

Currently used methods for representing geographical information are inadequate because they do not tolerate imprecision. This leads to information loss and inaccuracy in analysis. Such expressive inadequacy is largely due to the underlying membership concept of classical set theory. To improve information processing in GIS research and application, an alternative membership concept is required. In this paper, we explore the inadequacy imposed upon geographical information representation by classical set theory and address the problems of information loss. A fuzzy relational data model is defined which is more representative for geographical information. A GIS database for agricultural land resource management is created by using the data model and a new technique for assessing land suitability is developed. The fuzzy representation largely facilitates data analysis in this GIS. The methods are tested with data from North Java, Indonesia using a vector-based GIS software package, Arc Info, and the analysis results are presented.     

Integrating a GIS with an expert system to identify and manage dryland salinization

To manage secondary dryland salinization successfully a coordinated regional management approach must be implemented. This paper considers the development of an interactive land classification methodology that identifies key land areas associated with the problem and then conveys information regarding the decision-making process to the end user. The developed system, Salt Manager, utilizes an expert system, a geographic information system, remotely sensed information and a relational database management system to implement the land classification method. Consideration is given in the paper to the salinization process, the problem of system integration and the provision of contextual information via graphic and textual formats.     

Waterpoint management system in central district with ArcView GIS

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Wetland changes in Jianghan Plain and simulation with GIS

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