A Study On Feature-Based Object-Oriented Data Model For A Virtual GIS And Its Application

Virtual reality (VR) construct multi-dimensional spatial informationenvironment which have the ability of perfect interaction between man andcomputer, and Geographic information system (GIS) do well in the spatial geographicfeature analysis and processing. Therefore, integrating VR and GIS becomes essential inearth science study and practice. Virtual GIS becomes one of the major areas of GISwhich is a trend of information visualization virtual representation. The systemintegration of VR and GIS is being in the period from operational level to functional levelnowadays. Compared with rudimentary level and operational level, the functional levelmainly obtains data sharing by database mode, which have the powerful spatial-temporalefficiency. Therefore, a new data model must be designed by system developer for storingGIS data,multimedia data or other kind of data, by which user can get spatial attributesand non-spatial attributes of the "real" world in the most natural way.On the basis of data models that are applied in the fields of CAD, virtual reality andsimulations, a new feature-based object-oriented data model (FOVGISDM) for virtualGIS is initiated, in which feature-based modeling techniques and object-orientedapproaches are applied. The main contents of this dissertation are as follow:(1)First of all, the research background of virtual GIS is reviewed. We mainlyinvestigate the development trend of virtual reality and multi-dimensional GIStechniques. In terms of the research progress of virtual GIS, the purpose and significanceof the research is stated.(2)With reference to the development trend of virtual GIS, the integration principlesof VR and GIS are discussed in detail. Four VR and GIS integration methods arelisted on the basis of integration principles. Their system structures and characteristics areelaborated, respectively. The four stages of the integration are illustrated. The currentstatus of the integration and its development trend are analyzed. Meanwhile the keyproblems exist in the VR and GIS integration is explored, which includes data, virtualscenery, web VRGIS, and so on. Suggestions and approaches are presented to providesome possible solutions in resolving these key problems.(3)Through a thorough analysis of the current data models used by Virtual GIS, thefeature-based virtual GIS conceptual model framework is established by thefeature-based modeling technique for the most level abstract scheme of virtualspatial-temporal information representation. The dissertation not only defines the conceptof feature in virtual GIS, but also discusses the way of organizing virtual spatial-temporalinformation by the feature. The conceptual model takes the spatial characteristic ofgeographic entity into count;moreover, considers the understanding of geographicobject's semantic information in the process of interaction between man and virtualgeographic environment. At the same time, the conceptual model emphasizes theintegrality of feature, unifies the attribute,relationship,behavior and scenario propertiesof feature into the basic element unit for managing and operating the data of virtual GISdata model efficiently.(4)Based the conceptual model, using object-oriented methodology, thefeature-based object-oriented virtual GIS data model (FOVGISDM) is constructed. Thedissertation analysis the structure of FOVGISDM, including to the description anddefinition of feature object,feature semantic object,feature geometry object. Using theUML modeling tool, the geographic feature class diagrams are constructed. We also givean example of building feature object for explanation. Furthermore, the featurerelationship of FOVGISDM is analyzed systemically, especially the geometryrelationship and semantic relationship between feature objects.(5)The feature-based object-oriented virtual GIS database is be designed andrealized for virtual GIS data management with Oracle ORDB management model. Thedissertation introduces the basic steps of database design and the specific contents of eachdesign process in detail. After FOVGISDM is expressed as seven kinds of featureelement explicitly and integrally in the logical structure design step, the structure of tablestorage is be introduced in the physical structure design step. Each object data typeinvolved in the virtual GIS database is also stated in detail. Furthermore, we take examplefor the implementation of city virtual scene database.(6)Making use of the new data model, a Client/Server structured distributed virtualGIS prototype system is implemented. This system manages the modeling data by theserver, and supports visiting a vast amount of data with high speed and gettingmulti-resolution or semantic information easily. Using the designed interface betweenprototype system and database, the client read or writes these scene data swimmingly.With Vega API and VC++ as exploiting tools, the experimental software UI platform ofvirtual GIS prototype system is developed. It realize the loading of virtual scene model ,parts of spatial query functions and other real-time simulation and virtual realityapplications, such as drive,fly motion model. Furthermore, the feature modeling steps ofprototype system and key techniques is stated in detail.