ISSN:1365-8816    

DOI:10.1080/13658819709506176

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper we present a new technique to improve the performance of spatial access methods by minimizing redundancy: the oversize shelf. Oversize shelves are additional disk pages that are attached to the interior nodes of a treebased spatial access method (such as the R-tree or the cell tree). These pages are used to accommodate very large data objects in order to avoid their excessive fragmentation. Whenever inserting a new object into the tree, one now has to decide whether to store it on an oversize shelf or insert it into the corresponding subtrees. For this purpose, we developed an analytic model for the behaviour of dynamic spatial access methods under insertion and deletions. The model yields a threshold value for the size of an object, such that it is more favourable to put it on the oversize shelf if and only if its size is greater than the threshold value. Otherwise the insertion into the corresponding subtrees is preferable. Practical experiments indicate that this policy results in a faster computation of search queries, and that the cell tree with oversize shelves is one of the most efficient spatial access methods currently available.

ISSN:1365-8816    

DOI:10.1080/136588197242473

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper considers a model for positional uncertainty in maps with applications in geographical information systems. Using the model it is shown how uncertainty in map boundaries can be assessed, represented and transmitted through set operations such as intersection (map overlaying). Expressions for uncertainty in lengths, perimeters and areas calculated from maps are given. Simulation of maps and other quantities of interest derived from them is also discussed. The ideas are illustrated with examples.

ISSN:1365-8816    

DOI:10.1080/136588197242482

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The aim of the work reported is to support regional planning tasks by providing co-workers who are situated at different locations with access to a GIS. Five technical challenges for application sharing are identified: multiple views, multi-user access, feedback about other users activities, conference management facilities and sustainable performance. A system is presented which re-uses an existing single-user GIS and encompasses a User Interface Management System (UIMS), knowledge-based techniques and agent support for group-work. This novel approach offers a solution to the technical challenges, while enhancing the usability of such systems.

ISSN:1365-8816    

DOI:10.1080/136588197242491

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper the modelling formalism of cellular automata (CA) is generalized and extended within Geo-Algebra, a mathematical generalization of map algebra capable of expressing a variety of dynamic spatial models and spatial data manipulations within a common framework. Map dynamics, that is, the integration of the spatial dynamics reflected in CA and the spatial data handling capabilities of map algebra, constitutes a critical element within a wider project which sets out to formulate a general framework for simultaneously supporting spatial database manipulations and static and dynamic modelling within GIS. Map dynamics can also allow the modelling of additional dynamic behaviours and phenomena such as adaptation, design, learning and gaming not currently expressible as GIS models.

ISSN:1365-8816    

DOI:10.1080/136588197242509

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper deals with variation in transferred data from a set of irregular zones (called source zones) to a set of regular zones (called target zones) through the point-in-polygon method (i.e., the method that transfers the attribute value of a source zone to a target zone if a representative point of the source zone is included in the target zone). First,the variation is written as a mathematical equation. Second, it is shown that among regular lattices of target zones, a regular hexagonal lattice gives the minimum variation. However, the difference in variation between a square lattice and a regular hexagonal lattice is very small. Third, under the condition that an allowable variation is less than 5 per cent (which is usually acceptable in practice), the safest (the most conservative) rule supported by a theory is that the point-in-polygon method should be used when the diameter of every source zone is less than 4 per cent of the length of the edge of a square cell. Last, a practical rule based upon empirical data is that the point-in-polygon method should be used when the perimeter of every source zone is less than around 20 per cent of the length of the edge of a square cell.

ISSN:1365-8816    

DOI:10.1080/136588197242518

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor