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Author: | Jean-François Doyon |
---|---|
Contact: | jdoyon at nrcan.gc.ca |
Author: | Jeff McKenna |
Contact: | jmckenna at gatewaygeomatics.com |
Last Updated: | 2010-11-07 |
MapServer can retrieve and display data from a WFS server. The following document explains how to display data from a WFS server using MapServer.
A WFS ( Web Feature Service ) publishes feature-level geospatial data to the web. This means that it is possible to use this data as a data source to render a map. In effect, this is not unlike having a shapefile accessible over the web, only it’s not a shapefile, it’s XML-Encoded geospatial data (GML to be exact), including both geometry AND attribute information.
In order to enable MapServer to serve WFS, it MUST be compiled against certain libraries:
Please see the MapServer UNIX Compilation and Installation HOWTO for detailed instructions on compiling mapserver with support for these librairies and features. For Windows users, look on the MapServer website to see if there are any binaries available that meet these requirements.
You must set the IMAGEPATH parameter in your mapfile since MapServer uses this directory to store temporary files downloaded from the remote WFS server. Windows users must specify a full path for IMAGEPATH, such as: IMAGEPATH “C:/tmp/ms_tmp/”
MAP
...
WEB
IMAGEPATH "/tmp/ms_tmp/"
IMAGEURL ...
END
...
END
A WFS layer is a regular mapfile layer, which can use CLASS objects, with expressions, etc.
As of MapServer 4.4, the suggested method to define a WFS Client layer is through the CONNECTION parameter and the layer’s METADATA. The necessary mapfile parameters are defined below:
METADATA: The LAYER’s must contain a METADATA object with the following parameters:
wfs_connectiontimeout (optional): The maximum time to wait for a remote WFS layer to load, set in seconds (default is 30 seconds). This metadata can be added at the layer level so that it affects only that layer, or it can be added at the map level (in the web object) so that it affects all of the layers. Note that wfs_connectiontimeout at the layer level has priority over the map level.
wfs_filter: This can be included to include a filter encoding parameter in the getFeature request (see the Filter Encoding Howto for more information on filtering). The content of the wfs_filter is a valid filter encoding element.
...
METADATA
"wfs_filter" "<PropertyIsGreaterThan><PropertyName>POP_RANGE</PropertyName>
<Literal>4</Literal></PropertyIsGreaterThan>"
END
...
wfs_geometryname (optional): The name of the geometry column used for spatial filtering in the filter parameter (Geometry by default). This parameter is used for ArcGIS or GeoServer WFS services as several geometry column can be choosed (or with a different default name to Geometry).
wfs_latlongboundingbox (optional): The bounding box of this layer in geographic coordinates in the format “lon_min lat_min lon_max lat_max”. If it is set then MapServer will request the layer only when the map view overlaps that bounding box. You normally get this from the server’s capabilities output.
wfs_maxfeatures (optional): Limit the number of GML features to return. Sensible values are integers greater than 0. If 0 is specified, no features will be returned.
wfs_request_method (optional): Can be set to “GET” to do a Get request to WFS servers that do not support Post requests. The default method in MapServer is Post.
...
METADATA
"wfs_request_method" "GET"
END
...
wfs_typename (required): the <Name> of the layer found in the GetCapabilities. An example GetCapabilities request is: http://demo.mapserver.org/cgi-bin/wfs?SERVICE=WFS&VERSION=1.0.0&REQUEST=GetCapabilities
wfs_version (required): WFS version, currently “1.0.0”
Note
Each of the above metadata can also be referred to as ‘ows_*’ instead of ‘wfs_*’. MapServer tries the ‘wfs_*’ metadata first, and if not found it tries the corresponding ‘ows_*’ name. Using this reduces the amount of duplication in mapfiles that support multiple OGC interfaces since “ows_*” metadata can be used almost everywhere for common metadata items shared by multiple OGC interfaces.
LAYER
NAME "continents"
TYPE POLYGON
STATUS ON
CONNECTION "http://demo.mapserver.org/cgi-bin/wfs?"
CONNECTIONTYPE WFS
METADATA
"wfs_typename" "continents"
"wfs_version" "1.0.0"
"wfs_connectiontimeout" "60"
"wfs_maxfeatures" "10"
END
PROJECTION
"init=epsg:4326"
END
CLASS
NAME "Continents"
STYLE
COLOR 255 128 128
OUTLINECOLOR 96 96 96
END
END
END # Layer
As of MapServer v4.4 the method of specifying all of the connection information in the CONNECTION parameter has beendeprecated. The preferred method is mentioned above. If the metadata is not provided, VERSION, SERVICE, and TYPENAME will be fetched from the CONNECTION, as shown below
CONNECTION "http://demo.mapserver.org/cgi-bin/wfs?SERVICE=WFS&VERSION=1.0.0&TYPENAME=continents"