摘要:

The spread function is a powerful operation for analysing a wide range of phenomena considered in geographical information systems (GIS). One important and common application of the spread functions is the calculation of distance on a map. Mathematical morphology is a technique extensively used in the area of image processing, and it has been applied to calculating distance using the spread function. Unfortunately, its computation time is extremely long. In this paper, we propose to reduce the computation time by using a hierarchical data structure. The proposed approach and algorithm are presented and experimental results demonstrate that a substantial speed up in computation time can be obtained.

ISSN:1365-8816    

DOI:10.1080/136588198241653

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper introduces a new hierarchical data structure that supports efficient insertion, deletion and two-dimensional range query operations on swath data. Three different spatial indexing methods were designed, implemented and compared on a large swath data set. Two of the methods are based on the Morton code sequence, and the third uses an R-tree for the index. A relational database management system (RDBMS) was used to build one of the Morton code sequence indexing methods. Experiments with the large scale data set show that R-tree indexing is superior to Morton sequence indexing by providing two to nine times faster two dimensional range search speed, occupying slightly less disk space, and supporting the range deletion operation. Time and space requirements for spatial indexing with the RDBMS were shown experimentally to be significantly worse than for the direct C code implementation of the Morton code sequence indexing.

ISSN:1365-8816    

DOI:10.1080/136588198241662

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A trace, defined as a set of points satisfying some constraints, is introduced to specify ranges in which interesting objects are located. The paper shows how the declarativeness of the query language is enhanced by introducing this concept, and how explicitly recognized traces have a significant impact on query optimization. Two typical spatial queries are considered: spatial select and join. For spatial select queries, one needs to collect together distance related conditions concerning the same spatial attribute and to recognize them as a trace; this trace is used against the spatial index (if any) defined on the attribute, for query optimization. The trace concept is then extended to a region (instead of constant objects in the plane). This is necessary for spatial join queries since the spatial objects, in terms of which join conditions are specified, are bound by a relation. Because the whole plane is usually divided into rectangular regions by R -tree indexing, we consider actual traces on the basis of rectangles. A region r of one join relation and a region s of another join relation are 'joinable' (contain potentially joinable tuples) if r (or s) intersects with the trace on the basis of s (or r). By recursively exploring the R -tree indexes on the join attributes from roots to leaves, one may figure out joinable pages before searching for the principal relations.

ISSN:1365-8816    

DOI:10.1080/136588198241671

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The paper describes a problem faced by National Statistical Offices when publishing the results of decennial censuses for small geographical areas. If they publish statistical tables for two or more sets of areas, users can compare the tables and produce new statistics for the areas formed by differencing, which may have populations below confidentiality thresholds. To investigate the problem, the authors construct a software system and carry out a series of experiments using a large synthetic population base for Yorkshire and Humberside. The results indicate that publishing statistics for zones close in size to the primary areas is not safe unless the zones have been carefully designed. However, publishing statistics for sufficiently large areas such as 5 km grid squares or postal sectors alongside enumeration districts is safe.

ISSN:1365-8816    

DOI:10.1080/136588198241680

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A locational error model for spatial features in vector-based geographical information systems (GIS) is proposed in this paper. Using error in points as the fundamental building block, a stochastic model is constructed to analyse point, line, and polygon errors within a unified framework, a departure from current practices which treat errors in point and line separately. The proposed model gives, as a special case, the epsilon band model a true probabilistic meaning. Moreover, the model can also be employed to derive accuracy standards and cartographic estimates in GIS.

ISSN:1365-8816    

DOI:10.1080/136588198241699

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Recently, several publications have appeared that relate to the strategic dimension of GIS: how can GIS be aligned with business strategies, what strategic opportunities does GIS offer? In the broad range of elements identified in these discussions the critical observer will find quite different connotations of the concept of 'information strategy'. This article aims to provide an integrative framework that identifies and relates the individual elements in the strategic GIS discussions. The main stages in the framework as proposed here are the identification of the GIS challenge, positioning GIS within the organization and positioning the organization in relation to GIS.

ISSN:1365-8816    

DOI:10.1080/136588198241707

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:1365-8816    

DOI:10.1080/136588198241716

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor