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Overview: WMS, WFS, WCS PDF Print E-mail
Written by Richard Marsden   
Monday, 09 February 2009 14:12

WMS (Web Map Service), WFS (Web Feature Service), and WCS (Web Coverage Service) are three web service standards from the Open Geospatial Consortium (OGC). These allow web clients to query and receive geographic information in the form of image, vector, or coverage data.

The open source GeoServer application is the reference implementation of a server for the WMS, WFS, and WCS standards. Further information can be found at:  http://geoserver.org/display/GEOS/Welcome

WMS is probably the best known of these three standards due to its widespread use by map servers to deliver map images. These images are typically in the form of raster tiles (PNG, GIF, or JPG), but they can also be in a vector format such as SVB or WebCGM. Requests are made using a standard web URL. Here is a hypothetical example taken from the specification:

http://a-map-co.com/mapserver.cgi?VERSION=1.3.0&REQUEST=GetMap&CRS=CRS:84&BBOX=-97.105,24.913,-78.794,36.358&WIDTH=560&HEIGHT=350&LAYERS=AVHRR-09-27&STYLES=&FORMAT=image/png&EXCEPTIONS=INIMAGE

As can be seen, the request includes the required data layer, image size, the bounding box, coordinate system, and image type.

In addition to image data, WMS can supply meta data about the available layers, server capabilities, and contact/publisher information.

Example WMS server implementations include ArcGIS, ArcIMS, MapGuide, UMN MapServer, Oracle MapViewer, and SuperMap. Example map clients that support WMS, include: ArcGIS, Google Earth, GRASS, Autodesk Map3D, MapInfo, NASA World Wind, OpenLayers, and QGis.

In contrast to the images served by WMS, WFS communicates geographic feature information. The client may choose to render these features itself, but the real power comes from being able to manipulate the features in a true GIS fashion. For example, the client could perform geographic calculations or act as a feature editor.

The WFS web service allows features to be queried, updated, created, or deleted by the client. Feature data is typically passed using the XML-based GML format using SOAP. Data can also be transferred as Keyword-value pairs using RPC. WFS is classed as a non-RESTful RPC type web service.

The WCS web service is used to transfer "coverages", ie. objects covering a geographical area. As with WFS, WCS is considered to be a non-RESTful RPC type service. It can be encoded with XML SOAP or keyword-value pair RPC.
Coverages can be a set of data points; a regular grid of points (or pixels); a set of segmented curves (eg. road paths); a set of Thiessen polygons; or a TIN triangulated irregular network (eg. terrain models). WCS These data locations can also carry range information data - eg. a terrain model would include height information.

WCS clients have been implemented in gvSIG and GDAL.

The open source GeoServer application is the reference implementation of a server for the WMS, WFS, and WCS standards. Further information can be found at:  http://geoserver.org/display/GEOS/Welcome

OGC standards can be found at the following pages:



Last Updated on Monday, 23 February 2009 08:39