Integrated 3D Modelling within a GIS

This paper describes the architecture of a truly integrated D GIS The system has two main components an extensible database Postgres and an extensible geographic front end GEO The database is extended with D geometric data types functions and a D access method The implementation of the D visualization is based on the graphics standard PEX The resulting system is again extensible and can be used as a framework for modelling and analyzing many kinds of D applications geology air space management terrain modelling etc INTRODUCTION The relational approach has proven to be very e ective for developing various types of information systems Methodologies and advanced tools are available for designing and implementing relational data models and associated applications e g CASE and GL tools However the relational databases are not capable of handling spatial informa tion as encountered in a Geographic Information System GIS e ciently We have therefore designed a D spatial extension van Oosterom Vijlbrief and imple mented this within the Postgres eRDBMS Together with a geographic front end called GEO Vijlbrief van Oosterom this system is a complete GIS For certain applications the current capabilities of GEO are not su cient a few examples are terrain modelling Douglas Gold Gold Charters Ramsden eRDBMS stands for extensible Relational DataBase Management System Stonebraker Rowe Stonebraker Rowe Hirohama Note that the functionality in Postgres is similar to the future SQL standard Robinson Tom as used in for example Illustra the commercial successor of the Postgres research DBMS Though we use Postgres examples in this paper the method is general and can be applied in combination with any eRDBMS the GIS contains elevation data of the Earth surface D data model which can be displayed and analyzed e g compute which areas are visible from a certain location geology Barrera V azquez G omez Calkins Xia Guan Carlson Jones the layers below the Earth surface rock sand oil water have to be modelled e g for exploration by an oil company air space management the space above the Earth surface is subdivided into D corridors and is allocated to airplanes shery monitoring or simulating the sh population and movements lat long po sition and depth in the Oceans cadastre the cadastral boundaries in tall buildings can be true D e g in the city of Amsterdam cartography Kraak certain cartographic techniques require D capa bilities to visualize thematic attribute information e g a PRISM map It is clear that we need a D GIS for these types of applications There are a number of di erent systems available for this purpose but they usually have one or more of the following drawbacks they are limited to D data models they are separate modules hard to integrate with the GIS if they are true D then they are usually quite speci c programs not general purpose GIS based on a DBMS Therefore we decided to design and implement our own D GIS modelling environment based on the GEO system Section describes the overall architecture of this system The subsequent Sections and give additional details w r t the Abstract Data Types ADTs for D geometric primitives and w r t the topological relationships in D space Examples of complex D spatial analyses are listed in Section The Graphic User Interface GUI and visualization are the topics of Section The paper is concluded in Section which also contains possible future work D GIS ARCHITECTURE As described in Vijlbrief van Oosterom an integrated GIS architecture has several advantages over a dual or layered GIS architecture consistency and e ciency Both thematic and spatial data are integrated within objects or features and stored in the same DBMS Further reality as captured in the data model is translated directly In a D or Digital Terrain Model DTM for every location x y an unique elevation z can be obtained There are three usual ways of representing these data contours Watson in analogy with normal paper maps TIN Peuker Fowler Little Mark Floriani Triangular Irregular Network and grid Mark with height values at regular distances as can be found in DLMS DTED DMA to the physical DBMS in the integrated architecture The advantages of the integrated architecture are valid for both D and D modelling Weibel Weibel de nes three levels of integration of the Digital Terrain Model DTM module with the GIS loose coupling GIS and DTM are separate and only exchange data sets functional integration DTM functions can be used through GIS interface Further les with a common data format are used and full database integration DTM and GIS are based on same DBMS and the user interface is also integrated Since the advantages of full database integration are also clear for true D applications not only for DTMs we decided to follow this approach in which both D data and functions are available within the same DBMS and GIS environment Geographic Information System Handling of 2D and 3D Spatial Data 3D visualization