Integration of GRASS Functionality in Web based SDI Service Chains

Bringing the full set of GIS (Geographical Information System) functionality into a SOA (Service-oriented Architecture) based environment is one of the substantial changes in the GIS domain. Standardized data access and coordinate transformation and visualization functionality are already available and commonly used in Spatial Data Infrastructures (SDI). Nevertheless, one problem still remains: SDIs do not offer real geoprocessing capabilities (as offered in classic desktop GIS) such as generalization or complex raster based operations. Therefore, the OGC (Open Geospatial Consortium) released the Web Processing Service (WPS) specification, which describes a standardized abstract interface to bring complex processing power to SOA-based GIS. Despite this existing specification, hardly any concrete implementations of these abstract concepts can be found, which offers a sufficient set of GIS functionality. Thus, it is promising to enhance a classic (desktop) GIS by a WPS interface to offer such existing GIS functionality in a SOA-based environment. This was the starting point to develop an approach for wrapping GIS functionality as a standardized service. This paper shows, that a semi-automatic approach to generate appropriate WPS interface descriptions for each GIS functionality is possible. However, the complex nature of spatial data often requires multiple processing steps. The creation of service chains addresses this aspect. This paper describes a BPEL-based approach to orchestrate geoprocessing workflows based on distributed processing services incorporating the wrapping approach. Finally, the developed concept is proven by applying it to a real world scenario, which monitors droughts in a Sub-Sahara region with a Normalized Differenced Vegetation Index (NDVI) calculated from earth observation data. The GRASS-enabled WPS has been developed by the Geoprocessing Community (www.52north.org/wps) at the 52°North initiative.