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OGC Web Service (OWS)

Contents 1 Background to OGC 2 Web Mapping Service 3 Web Feature Service 4 Web Coverage Service 5 References 6 Subsections of this Article 7 Information about this article 8 Contact

Background to OGC

The Open Geospatial Consortium (OGC) is a non-profit, international, voluntary consensus standards organization that is leading the development of standards for geospatial and location based services^[1]. The consortium includes more than 370 commercial, governmental, nonprofit and research organizations worldwide collaborating in an open consensus process to encourage development and implementation of standards for geospatial content and services. Standards are a fundamental enabling technology of the Internet and allow thousands for applications, vendor solutions, and technologies to be interoperable.The OGC Web Map Service standard is an example of interoperability achieved through open standards and has resulted in the dramatic increase in the use of on-line mapping.

OGC Web Services (OWS) are defined using open non-proprietary Internet standards; in particular the World Wide Web (WWW) standards of HTTP, Uniform Resource Locators (URLs), Multipurpose Internet Mail Extensions (MIME) types and the Extensible Markup Language (XML)^[2]. A web services is a self-contained, self-describing, modular applications that can be published, located, and invoked across the Web. Web services perform functions that can be anything from simple requests to complicated business processes. Once a Web service is deployed, other applications (and other Web services) can discover and invoke the deployed service.

Web Mapping Service

The OGC Web Map Service (WMS) is a specification that defines the behaviour of a service that produces spatially referenced maps dynamically from geographic information. It specifies operations to retrieve a description of the maps offered by a server to retrieve a map. WMS defines a “map” to be a portrayal of geographic information as a digital image file suitable for display on a computer screen. A map is not the data itself. WMS-produced maps are generally rendered in a pictorial format such as PNG, GIF or JPEG. WMS is applicable to pictorial renderings of maps in a graphical format; it is not applicable to retrieval of actual feature data or coverage data values^[3].

WMS supports three operations:

1. GetCapabilities returns service-level metadata, which is a description of the service's information content and acceptable request parameters;
2. GetMap returns a map image whose geospatial and dimensional parameters are well defined;
3. GetFeatureInfo (optional) returns information about particular features shown on a map.

Web Feature Service

The OGC Web Map Service (WMS) allows a client to overlay map images for display served from multiple Web Map Services on the Internet. In a similar fashion, the OGC Web Feature Service (WFS) allows a client to retrieve and update geospatial data encoded in Geography Markup Language (GML) from multiple Web Feature Services^[4].

A WFS defines the interfaces for data access and manipulation operations on geographic features using HTTP as the distributed computing platform. A web user or service can combine, use and manage geodata -- the feature information behind a map image -- from different sources by invoking the following WFS operations on geographic features and elements:

• Create a new feature instance
• Delete a feature instance
• Update a feature instance
• Lock a feature instance
• Get or query features based on spatial and non-spatial constraints

Web Coverage Service

The OGC Web Coverage Service (WCS) defines a standard interface and operations that enables interoperable access to geospatial "coverages". The data served by a WCS is grid data usually encoded in a binary image format.and typically refers to content such as satellite images, digital aerial photos, digital elevation data, and other phenomena represented by values at each measurement point^[5].

Unlike the WMS, which portrays spatial data to return static maps (rendered as pictures by the server), the Web Coverage Service provides available data together with their detailed descriptions; defines a rich syntax for requests against these data; and returns data with its original semantics (instead of pictures) which may be interpreted, extrapolated, etc. – and not just portrayed.

Unlike WFS, which returns discrete geospatial features, the Web Coverage Service returns coverages representing space-varying phenomena that relate a spatio-temporal domain to a (possibly multidimensional) range of properties.

References

1. ↑ Open Geoospatial Consortium
2. ↑ OGC Reference Model
3. ↑ Web Map Service Implementation Specification
4. ↑ Web Feature Service Implementation Specification
5. ↑ Web Coverage Service Implementation Specification

Subsections of this Article

No subsections available

Information about this article

Short title: OGC Web Services

Description: A web services is a self-contained, self-describing, modular applications that can be published, located, and invoked across the Web.

Expertise level: expert

Author: Greg Reed

Approval status: approved

Approved by: Greg Reed

Last change: 2010-6-9

Subsection of: Geospatial Data Concepts

Contact

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