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A variety of free, open source GIS tools is now available for geo-related processing. The Web processing service (WPS) uses Web service technology for spatial calculations or easy access to models on the Internet in contrast to traditional geospatial processing, which is standalone, inefficient and often requires purchase of expensive software. A number of standards-compliant geospatial Web services have been developed using geographic resources analysis support system (GRASS) functions to manipulate rasters and vectors, and to process satellite image data. The paper adopts the WPS mechanism to expose the existing geospatial processing algorithms in the Web services as the interoperable WPS processes. A 52deg North WPS following the open geospatial consortium (OGC) standard is used supports the server. The key problem is that the version used with GRASS is incompatible with the version used with WPS. The way to address this challenge is to convert the data structure from WPS XML data input to an intermediate format compatible with GRASS. An open source GeoTools feature model would be a major undertaking. Two typical geospatial processes from the WPS would be invoked to handle geospatial data from Web coverage service (WCS) and Web feature service (WFS). These two cases illustrate that the WPS-enabled algorithm is easily accessed and easily integrated into scientific workflow systems in geospatial modeling. The biggest advantage of is its extremely high efficiency and low cost.