Web Coverage Service
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The Open Geospatial Consortium Web Coverage Service Interface Standard (WCS) provides an interface allowing requests for geographical coverages across the web using platform-independent calls. The coverages are objects (or images) in a geographical area, whereas the WMS interface or online mapping portals like Google Maps return only an image, which end-users cannot edit or spatially analyze. The XML-based GML furnishes the default payload-encoding for transporting the geographic features, but other formats like shapefiles can also serve for transport. In early 2006, the OGC members approved the OpenGIS GML Simple Features Profile [1].
The OGC membership defined and maintains the WCS specification. Among implementations are a Open Source WCS reference implementation, called GeoServer.
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[edit] Overview
The basic Web Coverage Service allows querying and retrieval of coverages.
A WCS describes discovery, query, or data transformation operations. The client generates the request and posts it to a web feature server using HTTP. The web feature server then executes the request. The WCS specification uses HTTP as the distributed computing platform, although this is not a hard requirement.
There are two encodings defined for WCS operations:
- XML (amenable to HTTP POST/SOAP)
- Keyword-Value pairs (amenable to HTTP GET/Remote procedure call)
In the taxonomy of Web Services, WCS is best categorized as a non-RESTful RPC type service.
[edit] Data
Data may be available in several formats, such as DTED, GeoTIFF, HDF-EOS, or NITF.
Several types of data layers are supported:
- series of points, such as locations of samples
- regular grid of pixels or points, which might represent a photo
- set of segmented curves, often used for road paths
- set of Thiessen polygons, used to analyse spatially distributed data such as rainfall measurements
- triangulated irregular network(TIN), often used for terrain models
Ranges of information may be attached to locations, such as average wind speed or yield by crop type.
