Global Positioning System Reference
In-Depth Information
Geoprocessing Web Services
The term geoprocessing encompasses a computational operation to
manipulate geospatial data. Examples are network analysis and coordinate
transformation, thematic classifi cation, and geocoding to name a few.
Geoprocessing web services extend geoprocessing capabilities according
to the SOA principles (Zhao et al. 2012). In such a context, the Open
Geospatial Consortium (OGC) 21 has defi ned a set of web service interfaces,
communication protocols, and data encodings for discovering, accessing
and visualizing geospatial data as well as executing geoprocessing
operations on the Web in a standard way (Lee and Percivall 2008). Further
readings relating OGC service specifications applied to varied application
domains are well documented in the literature (Reichardt 2010; Foerster et
al. 2011; Zhao et al. 2012).
One of these OGC service specifi cations is the Web Processing Service
(WPS) specifi cation (Schut 2007). The OGC WPS specifi cation defi nes a
service interface to expose computational operations and algorithms as
a web service. In contrast to traditional desktop-based geoprocessing
implementations, WPS-enabled services are fl exible and remotely accessible
algorithms available and inherit the benefi ts from service-based modeling
and web services (Kiehle 2006).
The notion of process is central to WPS services (Granell et al. 2008). To
run a process implies the following steps: (i) to fi nd geospatial data required
by the process, (ii) to initiate the process, (iii) to control the output, and
fi nally (iv) to make the results available to the client.
To follow the above steps an instance of a WPS service must offer three
public methods to the client applications. These methods can be called using
either HTTP-GET in combination with key-value pair (KVP), or HTTP-POST
and XML documents. Its getCapabilities and describeProcess methods offer
service and process metadata respectively, while the execute method triggers
a concrete process. Figure 6 shows how a client communicates with a WPS
service instance through the above three types of requests.
Emerging Approaches for Geo-enabled Workfl ows
This section outlines recent works that combine the two factors of the
left part of the equation from the chapter title, workfl ows systems and
geoprocessing web services, to lead to a kind of geo-enabled (scientifi c
and business) workfl ows. Such experiments and proof-of-concept tools for
21 http://www.opengeosatial.org
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