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
hugentobler@karto.baug.ethz.ch
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.