Sql Supported Spatial Analysis for Web-gis

Spatial analysis is a fundamental function for geographic information systems. Although it is popular in many commercial desktop GIS packages, this capability is very limited in a Web-GIS environment, especially when relational database is used for geospatial data management. This paper proposes and prototypes a methodology to enhance spatial analysis capabilities of Web-GIS by extending and enhancing the standard query language (SQL) in relational database. The paper first discusses the suitability of available SQL standards for complex spatial analysis. Unlike many recent studies, we have selected OGIS SQL as our spatial query standard to be enhanced with advanced spatial analysis capabilities. OGIS SQL standard contains a set of spatial data types and functions that are crucial for spatial data querying. In our work, OGIS SQL has been implemented in a Web-GIS based on open sources. Supported by spatial-query enhanced SQL, typical spatial analysis functions in desktop GIS are realized at the client side. These functions include distance, buffer, intersection, map overlay and feature fusion. User specific data are also supported. In this way, the spatial analysis can be implemented for spatial data from both server side and client side. The client side is programmed in Java. Two types of query interfaces are provided in client side, one is command line mode for experience users to input SQL directly; the other is the visual mode for common users. In the view mode, SQL can be generated by drag-and-dropping icons. The server side is backed on open source databases: mySQL, PostgreSQL/PostGIS and java serverlet technology. Geographic Markup Language (GML) is tested to return query results to client side and export spatial data.