Quadtree storage of vector data†

Abstract

Vector data storage has various advantages in a cartographic or geographical information system (GIS) environment, but lacks internal spatial relationships between individual features. Quadtree structures have been extensively used to store and access raster data. This paper shows how quadtree methods may be adapted for use in spatially indexing vector data. It demonstrates that a vector quadtree stored in floating point representation overcomes the classical problem with raster quadtrees of data approximation. Examples of vector quadtrees applied to realistic size data sets are given     

A spatial analytical perspective on geographical information systems

Abstract

The field of geographical information systems (GIS) is reviewed from the viewpoint of spatial analysis which is the key component of the familiar four-part model of input, storage, analysis and output Input is constrained by the limits of manual methods and problems of ambiguity in scanning. The potential for developments in output is seen to be limited to the query mode of GIS operation, and to depend on abandoning the cartographic model. Discussion of storage methods is organized around the raster versus vector debate and the need to represent two spatial dimensions in one. A taxonomy of GIS spatial analysis operations is presented together with a generic data model. Prospects for implementation are discussed and seen to depend on appropriate scales of organization in national and international academic research.     

The GEO VIEW design A relational data base approach to geographical data handling

Abstract

Digital map data are currently available based on a variety of data structures, depending on the uses to which the data are to be put Within the major categories of vector and raster data, as well as other structures, there is a multiplicity of data formats. Further to this, data for digital map coordinates are frequently stored in a different way from attribute data pertaining to points, lines and polygons. Given these problems, this paper investigates the possibility of handling different kinds of data structures, as well as both coordinate and attribute information within a unified conceptual scheme. This scheme is expressed in terms of the design of an integrated geographical information system called GEO VIEW, which can be implemented in a relational data base environment. The structure of the tables in the data base is outlined, together with the methodology for coding different kinds of data structure into a standard form. Examples of queries are provided, using the SQL query language, to indicate how the system might be used and problems in optimizing spatial searching on a data base of this kind are addressed.     

Development and test of an error model for categorical data

Abstract

An error model for spatial databases is defined here as a stochastic process capable of generating a population of distorted versions of the same pattern of geographical variation. The differences between members of the population represent the uncertainties present in raw or interpreted data, or introduced during processing. Defined in this way, an error model can provide estimates of the uncertainty associated with the products of processing in geographical information systems. A new error model is defined in this paper for categorical data. Its application to soil and land cover maps is discussed in two examples: the measurement of area and the measurement of overlay. Specific details of implementation and use are reviewed. The model provides a powerful basis for visualizing error in area class maps, and for measuring the effects of its propagation through processes of geographical information systems.     

Integration of spatial data in vector and raster formats in a geographic information system environment

This paper examines the common methods for converting spatial data sets between vector and raster formats and presents the results of extensive benchmark testing of these procedures. The tests performed are unique in this field since: (1) they used both synthetic and real test data sets; (2) they measured conversion quality, accuracy and efficiency, not just how fast the procedure operated; and (3) they were conducted in a generic geographic information system (GIS) environment without the aid of specialized computer hardware. The results show that the best overall techniques are the ones which take advantage of spatial relationships inherent in the data sets. These were the Scan Line algorithm for vector to raster conversions and the Boundary Linking algorithm for raster to vector conversions.     

Comparison of existing methods for building triangular irregular network,models of terrain from grid digital elevation models

Abstract

Triangulated irregular networks (TINs) are increasingly popular for their efficiency in data storage and their ability to accommodate irregularly spaced elevation points for many applications of geographical information systems. This paper reviews and evaluates various methods for extracting TINs from dense digital elevation models (DEMs) on a sample DEM. Both structural and statistical comparisons show that the methods perform with different rates of success in different settings. Users of DEM to TIN conversion methods should be aware of the strengths and weaknesses of the methods in addition to their own purposes before conducting the conversion.     

Many sorted algebraic data models for GIS

Although many GIS data models are available, a declarative, operational, well-defined, implementation-independent, and object-oriented language is lacking. Based on the theory of many sorted algebra, this work presents a family of geometric data models. Some geographical data models of urban information systems are illustrated using homomorphism. According to the results, the preferred characteristics of mixing declarative and operational statements, multiple representations, tight interdependency among objects, and integration of vector and raster based systems can be achieved through this mechanism.     

Real-time data collection quality assurance models in three-dimensional spatial information systems

Abstract

Databases used in geographical information systems must be supplied with current data. Maps are usually out of date when they are published. Satellite imagery and aerial photographs supply up-to-date three-dimensional data. Three different models for real-time quality assurance control in three-dimensional data collection for geographical information systems are discussed. Emphasis is placed on the visual detection of ‘blunders’ in three-dimensional data. One data collection quality assurance model has been implemented in the Photogrammetric Analysis Laboratory at Purdue University. An example from this system is given and the precision and speed of digitization of three-dimensional data are discussed.     

The development of geographical information systems in Japan†

Abstract

Geographical information systems are not as popular in Japan as they are in North America, but they have recently been attracting keen interest from national and local governments. This paper reviews (I) the present status of the introduction and use of geographical information systems in Japan, (2) national and local digital geographical information systems in Japan.     

Computing aspects of a large geographic information system for the European Community

Abstract

The CORINE programme (Co-ordinaled' Information on the European Environment) has been underway since 1985. Its purpose is to provide information on the environment of the entire European Community in a form suitable for assisting policy making. Such data must be accurate, integrated and readily available to the personnel for whom the system is designed. The system must be capable of dealing with large amounts of spatially-linked data from many different sources, in text, vector or raster form. The use of a geographic information system (GIS) is therefore essential. This paper describes the use of an interim system as a ‘bed’ for beginning the process of acquiring and integrating data. The data sets available are soils, climate, topography and ‘biotopes) (important areas for nature conservation). A data transfer format has been devised to provide for ease of transfer between various sites in the European Community with different mainframe computers. The interim system ensures that the needs of users can be defined and provides valuable user experience before a permanent system is installed. Other issues examined include the use of national and international networks and problems of integrating data when incorporating existing digital data from disparate sources into a large GIS.     

An event-based spatiotemporal data model (ESTDM) for temporal analysis of geographical data

Abstract

Representations historically used within GIS assume a world that exists only in the present. Information contained within a spatial database may be added-to or modified over time, but a sense of change or dynamics through time is not maintained. This limitation of current GIS capabilities has recently received substantial attention, given the increasingly urgent need to better understand geographical processes and the cause-and-effect interrelationships between human activities and the environment. Models proposed so-far for the representation of spatiotemporal data are extensions of traditional raster and vector representations that can be seen as location- or feature-based, respectively, and are therefore best organized for performing either location-based or feature-based queries. Neither form is as well-suited for analysing overall temporal relationships of events and patterns of events throughout a geographical area as a temporally-based representation.

In the current paper, a new spatio-temporal data model is proposed that is based on time as its organizational basis, and is thereby intended to facilitate analysis of temporal relationships and patterns of change through time. This model is named the Event-based Spatio Temporal Data Model (ESTDM). It is shown that temporally-based queries relating to locations can be implemented in an efficient and conceptually straightforward manner using ESTDM by describing algorithms for three fundamental temporally-based retrieval tasks based on this model: (1) retrieving location(s) that changed to a given value at a given time, (2) retrieving location(s) that changed to a given value over a given temporal interval, and (3) calculation of the total area that has changed to a given value over a given temporal interval. An empirical comparison of the space efficiency of ESTDM and compressed and uncompressed forms of the ‘snapshot’ model is also given, showing that ESTDM is also a compact representation of spatio-temporal information.     

PAN graphs An aid to GIS analysis

Abstract

Many data structures are possible for the storage of topological information for computer-based maps. The PAN graph is here suggested as an aid in the selection of a strategy appropriate to the application. Examples are given for the mapping of triangular networks and Thiessen polygons. Application of the technique is appropriate to both education in, and design of, spatial data structures for automated cartography and geographical information systems     

Bibliography of Journal Articles on Educational Media 1956-1966

Abstract

Many universities are introducing courses to teach students the principles of geographic information systems (GIS). In addition to lectures, exercises with commercial GIS software are offered to show basic operations. Although students learn to execute such operations, the software may hide their internal structure and logic. We propose using a spreadsheet program as a teaching tool for raster operations such as filter and overlay. Spreadsheets offer a practical way to demonstrate and experiment with raster operations, because the raster structure is captured in the form of rows and columns. With this tool, students are able to perform and visualize operations as well as to see how the data are processed by the algorithms. Our approach is new in that we concentrate on the algorithms of operations. We make explicit which raster functions are actually evaluated when performing a particular operation. We conclude that there are good reasons for using spreadsheets in comparison to traditional GIS software when teaching raster operations. These are demonstration in class, simple user interface, familiarity to students, low cost, flexibility of changing cell values, ease of changing parameters, easy programming environment, and the possibility to look behind the scenes of operations by viewing the code.     

Coordinating hazardous waste management activities using geographical information systems

Abstract

This paper describes a framework for the role of geographical information systems (GIS) in the monitoring and management of hazardous waste sites. Compilation of required information, incorporation of existing strategies for waste monitoring, analysis of these data in a GIS environment and the integration of computerized models for transport processes are discussed. Examples for the analysis of spatial data using techniques of cartographic overlay and the implementation of geo-statistical methods on monitoring data are provided from work in progress by the authors. These examples are set in the context of developing a fully integrated monitoring and management system utilizing GIS technology.     

Environmental decision support system project: an exploration of alternative architectures for geographical information systems

Abstract

Recent changes in information technology offer the opportunity to explore alternative architectures for geographical information systems (GIS) which might better support advanced applications. This paper describes the architecture and implementation of the environmental decision support system (EDSS), a prototype GIS tool kit. The architecture is based on a simple yet powerful systems model using only data collections, views and operations as the basic entity types. The design of the user interface, data management and data analysis within the model are outlined, with particular emphasis on the advanced facilities for which implementation is simplified by the architecture. A prototype applications system, BANKSIA, is also described.     

土壤碳库研究中土壤数据从矢量到栅格的等精度转换

矢量数据转换成栅格数据是多数区域土壤碳库研究中数据准备的关键步骤。本研究以太湖地区1:5万、1:50万、1:400万3个比例尺土壤矢量数据库为基础,分别转成不同分辨率的栅格数据;基于不同比例尺和栅格分辨率数据,研究水稻土表层(0～20cm)的土壤类型数量、面积、有机碳储量以及有机碳密度变化,并以矢量数据获得的这4个指标为基准,用相对变异百分数(VIV)来判别不同栅格数据与其对应比例尺土壤矢量数据之间的精度差异。结果表明,在4个指标的|VIV|<1%前提下,3个比例尺矢量数据分别转换成0.2km×0.2km、1km×1km、9km×9km的栅格数据,既保证数据转换过程中精度要求,又避免了数据冗余。土壤数据比例尺与栅格分辨率等精度转换对应关系可描述为y=0.0225x-0.01233(R²=0.999),对区域土壤碳循环研究具有重要参考价值。     

Natural trees—neighbourhood-location in a nutshell

Abstract

We present the notion of a natural tree as an efficient method for storing spatial information for quick access. A natural tree is a representation of spatial adjacency, organised to allow efficient addition of new data, access to existing data, or deletions. The nodes of a natural tree are compound elements obtained by a particular Delaunay triangulation algorithm. Improvements to that algorithm allow both the construction of the triangulation and subsequent access to neighbourhood information to be O(N log N). Applications include geographical information systems, contouring, and dynamical systems reconstruction.     

Utilizing discriminant function analysis with a geographical information system to model ecological succession spatially

Abstract

A raster/quadtree geographical information system (GIS) was established For a 932 ha natural area in central Missouri. The GIS contained map layers depicting vegetative cover from 1939 to 1982, soils, topographic aspect and distance from a forest seed source. Discriminant function analysis was used to quantify and describe ecological succession on the area during this period. The calibration of discriminant functions is discussed, as are the statistical and spatial validations of the model. It was concluded that this approach provides a useful technique to examine long-term temporal phenomena in a spatial context.     

矢量数据向栅格数据转换的一种改进算法

地理信息系统的发展与空间数据结构的优化密不可分,栅格数据与矢量数据之间的高效转换是GIS的关键技术之一。由于栅格数据十分有利于空间分析中的叠置分析,因而通常需要将矢量数据转换成栅格数据。该文分析对比了地理信息系统的两种基本数据结构,在总结已往矢量数据转换为栅格数据方法的基础上,依据边界代数多边形填充算法的基本原理,结合绘图作业时采用的正负法,提出了一种改进的折线边界(数据串)跟踪方法。该算法原理简单,不需进行复杂的距离比较运算,运算速度快,并且通过简单的角度判断保证了填充的精度。