This driver can connect to a OGC WFS service. It supports WFS 1.0.0 and WFS 1.1.0 protocols. GDAL/OGR must be built with Curl support in order to the WFS driver to be compiled. Usually WFS requests return results in GML format, so the GML driver should generally be set-up for read support (thus requiring GDAL/OGR to be built with Xerces or Expat support). It is sometimes possible to use alternate underlying formats when the server supports them (such as OUTPUTFORMAT=json).
The driver supports read-only services, as well as Transactionnal ones (WFS-T).
Additionnal optional parameters can be specified such as TYPENAME, VERSION, MAXFEATURES as specified in WFS specification.
The name provided to the TYPENAME parameter must be exactly the layer name reported by OGR, in particular with its namespace prefix when its exists. Note: starting with GDAL 1.10, several type names can be provided and separated by comma.
It is also possible to specify the name of an XML file whose content matches the following syntax (the <OGRWFSDataSource> element must be the first bytes of the file):
<OGRWFSDataSource> <URL>http://path/to/WFS/service[?OPTIONAL_PARAMETER1=VALUE[&OPTIONNAL_PARAMETER2=VALUE]]</URL> </OGRWFSDataSource>
Note: the URL must be XML-escaped, for example the & character must be written as &
At the first opening, the content of the result of the GetCapabilities request will be appended to the file, so that it can be cached for later openings of the dataset. The same applies for the DescribeFeatureType request issued to discover the field definition of each layer.
The service description file has the following additional elements as immediate children of the OGRWFSDataSource element that may be optionally set.
Some servers (such as MapServer >= 6.0) support a vendor specific option, STARTINDEX, that allow to do the requests per "page",
and thus to avoid downloading the whole content of the layer in a single request. The OGR WFS client will use paging when the OGR_WFS_PAGING_ALLOWED
configuration option is set to ON. The page size (number of features fetched in a single request) is limited to 100 by default.
It can be changed by setting the OGR_WFS_PAGE_SIZE configuration option.
WFS 1.1 specification has clarified that the first feature in paging is at index 0. But some server implementations of WFS 1.1 have considered that it was at index 1 (including MapServer <= 6.2). Starting with OGR 1.10, the default base start index is 0, as mandated by the specification. The OGR_WFS_BASE_START_INDEX configuration option can however be set to 1 to be compatible with the server implementations that considered the first feature to be at index 1.
Those 3 options (OGR_WFS_PAGING_ALLOWED, OGR_WFS_PAGE_SIZE, OGR_WFS_BASE_START_INDEX) can also be set in a WFS XML description file with the elements of similar names (PagingAllowed, PageSize, BaseStartIndex).
Starting with OGR 1.10, the WFS driver will read the GML content as a stream instead as a whole file, which will improve interactivity and help when the content cannot fit into memory. This can be turned off by setting the OGR_WFS_USE_STREAMING configuration option to NO if this is not desirable (for example, when iterating several times on a layer that can fit into memory). When streaming is enabled, GZip compression is also requested. It has been observed that some WFS servers, that cannot do on-the-fly compression, will cache on their side the whole content to be sent before sending the first bytes on the wire. To avoid this, you can set the CPL_CURL_GZIP configuration option to NO.
Write support is only enabled when the datasource is opened in update mode.
The mapping between the operations of the WFS Transaction service and the OGR concepts is the following :
There are a few caveouts to keep in mind. OGR feature ID (FID) is an integer based value, whereas WFS/GML gml:id attribute is a string. Thus it is not always possible to match both values. The WFS driver exposes then the gml:id attribute of a feature as a 'gml_id' field.
When inserting a new feature with CreateFeature(), and if the command is successfull, OGR will fetch the returned gml:id and set the 'gml_id' field of the feature accordingly. It will also try to set the OGR FID if the gml:id is of the form layer_name.numeric_value. Otherwise the FID will be left to its unset default value.
When updating an existing feature with SetFeature(), the OGR FID field will be ignored. The request issued to the driver will only take into account the value of the gml:id field of the feature. The same applies for DeleteFeature().
It is possible to surround those operations between OGRLayer::StartTransaction() and OGRLayer::CommitTransaction(). The operations will be stored into memory and only executed at the time CommitTransaction() is called.
The drawback for CreateFeature() is that the user cannot know which gml:id have been assigned to the inserted features. A special SQL statement has been introduced into the WFS driver to workaround this : by issuing the "SELECT _LAST_INSERTED_FIDS_ FROM layer_name" (where layer_name is to be replaced with the actual layer_name) command through the OGRDataSource::ExecuteSQL(), a layer will be returned with as many rows with a single attribue gml_id as the count of inserted features during the last commited transaction.
Note : currently, only CreateFeature() makes use of OGR transaction mechanism. SetFeature() and DeleteFeature() will still be issued immediately.
"DELETE FROM layer_name WHERE expression" : this will result into a WFS delete operation. This can be a fast way of deleting one or several features. In particularly, this can be a faster replacement for OGRLayer::DeleteFeature() when the gml:id is known, but the feature has not been fetched from the server.
"SELECT _LAST_INSERTED_FIDS_ FROM layer_name" : see above paragraph.
(OGR >= 1.9.0)
A "hidden" layer called "WFSLayerMetadata" is filled with records with metadata for each WFS layer.
Each record contains a "layer_name", "title" and "abstract" field, from the document returned by GetCapabilities.
That layer is returned through GetLayerByName("WFSLayerMetadata").
(OGR >= 1.9.0)
A "hidden" layer called "WFSGetCapabilities" is filled with the raw XML result of the GetCapabilities request.
That layer is returned through GetLayerByName("WFSGetCapabilities").
ogrinfo -ro WFS:http://www2.dmsolutions.ca/cgi-bin/mswfs_gmap
ogrinfo -ro mswfs_gmap.xml
ogrinfo -ro WFS:http://www2.dmsolutions.ca/cgi-bin/mswfs_gmap popplace -spat 0 0 2961766.250000 3798856.750000
ogrinfo "WFS:http://www.tinyows.org/cgi-bin/tinyows" tows:world -ro -al -where "gml_id='world.2' or gml_id='world.3'"
ogrinfo -ro -al "WFS:http://v2.suite.opengeo.org/geoserver/ows" WFSLayerMetadata