The Open GIS Consortium OGC) has published a Request for Comment on a proposal for technologies and needed interfaces required for OpenGIS Web Coverage Service (WCS) Implementation Specification. The specification document "explains how WCS serves to describe, request, and deliver multi-dimensional coverage data over the World Wide Web. WCS emphasizes 'simple' coverages (defined on some regular, rectangular grid or tesselation of space) and anticipates other coverage types defined in the OpenGIS Abstract Specification. This includes pixel and point grids, including aerial and satellite images and digital terrain models. Web Coverage Service provides access to intact (unrendered) geospatial information, as needed for client-side rendering, multi-valued coverages, and input into scientific models for advanced rendering and visualization clients."

Bibliographic information: Request for Comment - OpenGIS Web Coverage Service. Edited by John D. Evans (NASA Geospatial Interoperability Office). Open GIS Consortium, Inc. Date: 2002-12-18. Reference: OGC 02-024r1. Version: 0.9. Category: Proposed OpenGIS Implementation Specification, Request for Comment. 75 pages. XML Schemas in ANNEX A. Chapters 6-9 present (respectively) Basic Service Elements, GetCapabilities operation, GetCoverage operation, and DescribeCoverageLayer Operation.

Overview

The Web Coverage Service (WCS) supports the networked interchange of geospatial data as "coverages" containing values or properties of geographic locations. Unlike the Web Map Service (WMS - OGC document #01-021r2), which filters and portrays spatial data to return static maps (server-rendered as pictures), the Web Coverage Service provides access to intact (unrendered) geospatial information, as needed for client-side rendering, multi-valued coverages, and input into scientific models and other clients beyond simple viewers.

The Web Coverage Service consists of three operations: GetCapabilities, GetCoverage, and DescribeCoverageType. The GetCapabilities operation returns an XML document describing the service and the data collections from which clients may request coverages. Clients would generally run the GetCapabilities operation and cache its result for use throughout a session, or reuse it for multiple sessions.

The GetCoverage operation of a Web Coverage Service is normally run after GetCapabilities has determined what queries are allowed and what data are available. The Get-Coverage operation returns values or properties of geographic locations, bundled in a well-known coverage format. Its syntax and semantics are similar to the WMS GetMap request, but several extensions support the retrieval of coverages rather than static maps. (from the Introduction)

Coverages: See the Geospatial Interoperability Reference Model for description: "Coverages are the other broad category of geospatial data; they describe a set of spatial locations (the 'domain') in terms of one or more characteristics (the 'range' or 'attribute values'). Examples might include a soil map (soil types of specific areas); a satellite image (brightness of a set of pixels), or a digital elevation model (regularly-spaced elevation data, or triangulated irregular spot elevations). Given the widespread use of aerial and satellite imagery, grid coverages (whose domain consists of a rectangular array of points, cells, or pixels) are an important special case..."

Details from the announcement:

At the Open GIS Consortium, Inc. (OGC) Technical and Planning Committee meetings, the Coverage Working Group, the OGC Technical Committee, and the OGC Planning Committee voted to release the proposed Web Coverage Service (WCS) Implementation Specification, for public comment, as a Request for Comment (RFC). The RFC details draft interfaces that allow gridded and certain non-gridded geospatial data on a server to be accessed and used by client software as input into spatial model, local rendering and other uses. The documentation is available online and comments are invited from any interested parties for 30 days, until Jan 17, 2003. After the Request for Comment period ends, and comments are assembled and addressed, the WCS RFC may be brought to a vote to become an Adopted OpenGIS Specification.

The Web Coverage Service (WCS) provides access to intact, raw data while WMS provides a static "picture" of a map. WCS' three key operations, GetCapabilities, GetCoverage, and DescribeCoverageType are designed to work with coverages (imagery, TINS and other types of gridded and non-gridded intelligent data). The GetCapabilities operation returns an XML document from the server that describes the service and the data collections available. The GetCoverage operation of a Web Coverage Service returns values or properties of geographic locations, bundled in a well-known coverage format.

Jeff Labonte, Director of the Canada's GeoConnections Program, stated that the Web Coverage Service is an important element that will further development of the Canadian Geospatial Data Infrastructure by promoting interoperability of important sources of information such as earth observation satellites and imagery.

NASA is the lead submitter on WCS. The submission team also includes BAE Systems, PCI Geomatics, IONIC Software s.a, George Mason University, Polexis, Inc., Intergraph Mapping and Geospatial Solutions, Cubewerx, Inc., Natural Resources Canada, and German Aerospace Center DLR.

OGC is an international industry consortium of more than 230 companies, government agencies and universities participating in a consensus process to develop publicly available interface specifications. OpenGIS Specifications support interoperable solutions that "geo-enable" the Web, wireless and location-based services, and mainstream IT. The specifications empower technology developers to make complex spatial information and services accessible and useful with all kinds of applications.

Related: OGC Geospatial One-Stop Portal Initiative (GOS-PI): "OGC is partnering with the National Aeronautics and Space Administration, the Federal Geographic Data Committee, the US Department of Agriculture, and the US Geological Survey under the auspices of Geospatial One-Stop to build a standards-based portal for geospatial information discovery, access, and mapping. This effort is part of a larger Geospatial One-Stop effort. Led by the Department of the Interior, Geospatial One-Stop is one of 24 US Office of Management and Budget E-Government initiatives to improve effectiveness, efficiency, and customer service throughout all layers of government..." See the E-Government Geospatial One-Stop website and announcement.