A DESIGN CONCEPT FOR IMPLEMENTING INTEROPERABLE CARTOGRAPHIC SERVICES BASED ON REUSABLE GIS COMPONENTS
M. Hugentobler, I. Iosifescu Enescu, L. Hurni
Institute of Cartography, ETH Zurich, Switzerland
The adoption of the web services paradigm and OGC (Open Geospatial Consortium) interoperability standards created new opportunities as well new challenges for web cartographic applications. In this respect, cartographers have now the chance of designing and implementing WMS (Web Map Service) instances that will keep compatibility and interoperability with existing OGC service instances and in the same time, that will implement cartographically enriched interfaces.
This paper presents an extensible design concept and a methodology for an efficient implementation of interoperable cartographic services based on open source Geographic Information System (GIS) libraries. The paper contains design considerations, analysis of required server components, collaboration between different components and a technical exemplification of the object oriented implementation concept for obtaining a functional cartographic service.
The proposed design concept contains the following components:
- A server class which controls the execution of the service requests having an interface called 'request handler' which hides the details (mainly input and output) of a specific platform or server technology (e.g. HTTP GET, POST, SOAP, CGI, FastCGI, etc.) from the main code.
- A map language describing the data and symbolisation. In the example implementation, an extended version of the OGC SLD (Styled Layer Descriptor) standard is used as map language.
- A configuration file for project configuration ('mapfile')
- (Existing GIS) libraries which do the map rendering
- A converter from map language to library classes
The application of this implantation design concept is demonstrated with the implementation of an extended web map service (a Map and Diagram Service) on top of Qt/QGIS libraries. The interaction of the different components is explained using sequence diagrams.
Finally the paper shows also the suitability of this design for supporting cartographic features for thematic mapping (e.g. diagrams), features which goes beyond current implementations of web map services.