多比例尺空间数据库的层次对象模型

多比例尺空间数据库是社会和技术发展到一定阶段后对地理信息系统提出的必然要求。本文分析了产生该问题的原因,多比例尺空间数据库的定义及相关性,回顾了多比例尺空间数据库建立的3种模型以及其组织结构、管理方式和优缺点。本文设计了层次对象模型作为多比例尺数据库实现的概念模型,将多比例尺表达分解为目标集合层次树和目标细节树的设计,详细论述了模型解决多比例尺数据管理的方法,最后讨论了多比例尺数据库的应用前景。

Hierarchical Object Model for Multi-scale Spatial Databases

People understand and communicate geographical information mainly by maps and a computer-based tool of GISs.In order to present a better knowledge about the geographical world, cartographers traditionally compile maps of different themes, times and scales.In digital environment, these three factors result in the problem of multiple representation model of geographical information.GISs provide various tools to achieve it.It organizes geographic features in digital database into different layers according to their themes, and in this way users can get proper visualization forms simply by turning on or off the corresponding geographical themes.On the point of time, say temporal factor, researchers have done a lot of work and proposed much solution.This paper discusses the last challenge. The last one, scale, has attracted people's attention in an even longer history.In analogue era, cartographic generalization is the most time and labor consuming part in map making.And in digital environment, GISs applications ask automation of geo-information generalization for lots of reasons, e.g.map making, computation efficiency, network transmission of spatial data, cognition on geographical world, but automatic generalization has been a stubborn task before researchers from the introduction of computer into geo-information processing.Numerous algorithms have been put forward for generalization operators executed on such features as point, line, area and network.However, to present, there is no generally satisfying solution to most applications.And multi-scale spatial database emerged as a tradeoff.In order to get multi-scale views of spatial databases (SDB), there are three approaches.The first scheme of multi-scale SDB is based on multiple scale versions of SDB.The second is based on integrated data structures.And the third is based on automatic geo-information generalization, which is the objective and cannot elegantly implement currently.So, this paper, as most feasible models, takes the second way.The authors design a multi-scale SDB model, named as Hierarchical Object Model (HOMO), to accommodate this problem.HOMO, which combines the objects aggregation hierarchical tree and object's detail hierarchical tree, stores the result of generalization at different scales efficiently and it can perform the operators of merge, aggregation and symbolization of features.The former structure, which is designed as Figure 3, deals with multiple views of compound objects.To single object, scale's changing may dramatically affect its representation.There are two kinds of changes in representation, which are detailed change and dimensional change.The object's detail hierarchical tree integrates both changes.The idea of HOMO is easy to be understood and can satisfactorily help to perform multi-scale spatial data manipulations.