Object-oriented Geospatial Model Studies, And Geometric Data Types

Geographic Information System (GIS) is a spatial information system which tasks are picking up , storage, administration, analysis and description of all or part of earth surface data (including atmospheric layer)related to spatial and geographic distribution. GIS has been made great progress in elementary theory, system design technique and application method since its initiation in 1960s.The development of GIS can be divided into three stages that form respectively three generations of software. Although the progress made in system structure and technique, these software are all based on map; that is to say , they all belong to the kind of traditional "Tomlinson" . But based on map can bring many restrictions and disadvantages to CIS application.In fact the problem of traditional GIS software lies in its model, which is dedicated to how to abstract, represent process, analyses and apply geographic entity data and the relations between them in a system . Recent years, with the increase of depth and extent of GIS application, new requirements to theory research emerge unceasingly. As far as model is concerned, the forth generation software should be characterized with spatial entity-oriented.The paper established the geographic spatial model based on the thinking of object-oriented; studied the structure of the model' s elementaryunit--geographic entity; brought forward the concept of geometric datatype which characterize entity's spatial feature in the structure; defined five kinds of geometric data types such as POINT, ARC, AREA, COMPOSITE ARC, COMPOSITE AREA; and formalized their collective operation using hypergraph. At the end of this paper writer studied preliminarily the method of entity query and analysis based on the model.Research result shows that the object-oriented geographic spatial model has stronger representative ability, is easier understood and accepted; using the concept of geometric data type unify the process method of attribute and spatial data, and simplify entity query and analyses. The topologic relations between entities, which are not been stored in explicit formulation in the model, can be achieved through collective operation of geometric object's hypergraph model. Compared with traditional HIS, the query and analyses ability of which based on new model are stronger.This paper also gives some proposals for further research work.