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WFS is an Open Geospatial Consortium specification. For more information about the format itself, see http://www.opengeospatial.org/. WFS allows a client to retrieve geospatial data encoded in Geography Markup Language (GML) from multiple Web Feature Services. GML is built on the standard web language XML. WFS differs from the popular Web Map Service specification in that WFS returns a subset of the data in valid GML format, not just a graphic image of data. Requesting capabilities using the GetCapabilities request to a WFS server returns an XML document showing what layers and projections are available, etc. Example of a WFS GetCapabilities URLhttp://www2.dmsolutions.ca/cgi-bin/mswfs_gmap ?VERSION=1.0.0 &SERVICE=wfs &REQUEST=GetCapabilities Example of the resulting XML from GetCapabiltiesExample B-1. Resulting XML from GetCapabilities... <FeatureTypeList> <Operations> <Query/> </Operations> <FeatureType> <Name>park</Name> <Title>Parks</Title> <SRS>EPSG:42304</SRS> <LatLongBoundingBox minx="-173.433" miny="41.4271" maxx="-13.0481" maxy="83.7466" /> </FeatureType> <FeatureType> <Name>road</Name> <Title>Roads</Title> <SRS>EPSG:42304</SRS> <LatLongBoundingBox minx="-148.059" miny="35.882" maxx="-33.7745" maxy="72.5503" /> </FeatureType> <FeatureType> <Name>popplace</Name> <Title>Cities</Title> <SRS>EPSG:42304</SRS> <LatLongBoundingBox minx="-172.301" miny="36.3541" maxx="-12.9698" maxy="83.4832" /> </FeatureType> </FeatureTypeList> ... Data access/connection method
WFS layers can be requested through a layer in a map file, or you can request the GML directly through the browser with a GetFeature request. You can specify a specific layer with the TypeName request. In a map file, the name/value pairs should be put into a METADATA object. You can limit the number of features returned in the GML by using the MaxFeatures option (e.g., &MAXFEATURES=100). Example of a WFS request directly through the browserThe following URL requests the GML for the layer road (see the earlier section, "Capabilities," for the possible layers available on this test server). The URL is all one line, broken up here for readability. http://www2.dmsolutions.ca/cgi-bin/mswfs_gmap ?VERSION=1.0.0 &SERVICE=wfs &REQUEST=getfeature&TYPENAME=road Map file exampleLAYER NAME "wfs_gmap_roads" STATUS DEFAULT TYPE LINE CONNECTIONTYPE WFS CONNECTION "http://www2.dmsolutions.ca/cgi-bin/mswfs_gmap? METADATA "wfs_version" "1.0.0" "wfs_srs" "EPSG:42304" "wfs_typename" "road" "wfs_request_method" "GET" "wfs_service" "WFS" END CLASS NAME "roads" COLOR 0 0 0 END END # layer |
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