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Introduction

The FEWS Web Feature is the Delft-FEWS implementation of the OpenGIS WFS 2.0 OGC standard and is available since 2023.01. It allows requesting GML or GeoJSON data for plots that have been configured in the FEWS grid display. The WFS service can be seen as a complementary to the WMS service as it supports only gridplot types that contain polygon data instead of grids, where the WMS service allows you to render these plots to images, the WFS service provides access to the underlying vector data. 

Only gridPlot items that have been configured in the grid display configuration to show polygon data can be currently be accessed as a WMS 'Feature Type'. Additional geographic information like configured LocationSets and s(hapefile) Map layers may also become available this way in the near future.

Developers documentation

For API Developers it is recommended to use the Open API Documentation. Please see: <Work in progress>

The official OpenGIS documentation consists of two documents, the OpenGIS Web Feature Service 2.0 Interface Standard and the OpenGIS Filter Encoding 2.0 Encoding Standard, both of which are ISO certified standards

WFS Request methods

The available request methods with their supported parameters are described here.

GetCapabilties

Get a list of the available polygon gridPlots, in WFS terminology these are 'FeatureTypes" and other information about the service. GetCapabilties will return its content as XML in accordance with the WFS 2.0 standard. Only the 2.0 version of this standard is supported.

Request parameters

  • the GetCapabilities request has no parameters

Response

When requesting the GetCapabilities an XML response with be given with all available polygon gridPlots. The XML schema unfortunately does not allow them to be nested by gridPlotGroups (unlike the WMS schema).

Example request

http://localhost:8080/FewsWebServices/wfs?request=GetCapabilities


Example xml response

<?xml version="1.0" encoding="UTF-8"?>
<WFS_Capabilities version="2.0.0" xmlns="http://www.opengis.net/wfs/2.0" xmlns:gml="http://www.opengis.net/gml/3.2" xmlns:fes="http://www.opengis.net/fes/2.0" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:deltares="http://deltares.nl" xsi:schemaLocation="http://www.opengis.net/wfs/2.0 http://schemas.opengis.net/wfs/2.0/wfs.xsd http://www.opengis.net/ows/1.1 http://schemas.opengis.net/ows/1.1.0/owsAll.xsd">
    <ows:ServiceIdentification>
        <ows:Title>WFS Unit tests</ows:Title>
        <ows:ServiceType>WFS</ows:ServiceType>
        <ows:ServiceTypeVersion>2.0.0</ows:ServiceTypeVersion>
    </ows:ServiceIdentification>
    <ows:ServiceProvider>
        <ows:ProviderName>Deltares</ows:ProviderName>
    </ows:ServiceProvider>
    <ows:OperationsMetadata>
        <ows:Operation name="GetCapabilities">
            <ows:DCP>
                <ows:HTTP>
                    <ows:Get xlink:href="http://localhost/FewsWebServices/wfs"></ows:Get>
                </ows:HTTP>
            </ows:DCP>
            <ows:Parameter name="AcceptVersions">
                <ows:AllowedValues>
                    <ows:Value>2.0.0</ows:Value>
                </ows:AllowedValues>
            </ows:Parameter>
            <ows:Parameter name="AcceptFormats">
                <ows:AllowedValues>
                    <ows:Value>text/xml</ows:Value>
                </ows:AllowedValues>
            </ows:Parameter>
        </ows:Operation>
        <ows:Operation name="DescribeFeatureType">
            <ows:DCP>
                <ows:HTTP>
                    <ows:Get xlink:href="http://localhost/FewsWebServices/wfs"/>
                </ows:HTTP>
            </ows:DCP>
            <ows:Parameter name="outputFormat">
                <ows:AllowedValues>
                    <ows:Value>application/gml+xml; version=3.2</ows:Value>
                </ows:AllowedValues>
            </ows:Parameter>
        </ows:Operation>
        <ows:Operation name="ListStoredQueries">
            <ows:DCP>
                <ows:HTTP>
                    <ows:Get xlink:href="http://localhost/FewsWebServices/wfs"/>
                </ows:HTTP>
            </ows:DCP>
        </ows:Operation>
        <ows:Operation name="DescribeStoredQueries">
            <ows:DCP>
                <ows:HTTP>
                    <ows:Get xlink:href="http://localhost/FewsWebServices/wfs"/>
                </ows:HTTP>
            </ows:DCP>
        </ows:Operation>
        <ows:Operation name="GetFeature">
            <ows:DCP>
                <ows:HTTP>
                    <ows:Get xlink:href="http://localhost/FewsWebServices/wfs"/>
                </ows:HTTP>
            </ows:DCP>
            <ows:Parameter name="outputFormat">
                <ows:AllowedValues>
                    <ows:Value>application/gml+xml; version=3.2</ows:Value>
                    <ows:Value>application/geo+json</ows:Value>
                    <ows:Value>application/json</ows:Value>
                </ows:AllowedValues>
            </ows:Parameter>
        </ows:Operation>
        <ows:Parameter name="AcceptVersions">
            <ows:AllowedValues>
                <ows:Value>2.0.0</ows:Value>
            </ows:AllowedValues>
        </ows:Parameter>
        <ows:Constraint name="ImplementsBasicWFS">
            <ows:NoValues/>
            <ows:DefaultValue>TRUE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsTransactionalWFS">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsLockingWFS">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="KVPEncoding">
            <ows:NoValues/>
            <ows:DefaultValue>TRUE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="XMLEncoding">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="SOAPEncoding">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsInheritance">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsRemoteResolve">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsResultPaging">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsStandardJoins">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsSpatialJoins">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsTemporalJoins">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ImplementsFeatureVersioning">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="ManageStoredQueries">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
        <ows:Constraint name="wfs:StoredQuery">
            <ows:NoValues/>
            <ows:DefaultValue>FALSE</ows:DefaultValue>
        </ows:Constraint>
    </ows:OperationsMetadata>
    <FeatureTypeList>
        <FeatureType>
            <Name>deltares:full_extent_cta_clean</Name>
            <Title>SFINCS full extent</Title>
            <DefaultCRS>urn:ogc:def:crs:EPSG::4326</DefaultCRS>
            <OtherCRS>urn:ogc:def:crs:EPSG::4326</OtherCRS>
            <OtherCRS>urn:ogc:def:crs:EPSG::3857</OtherCRS>
            <ows:WGS84BoundingBox>
                <ows:LowerCorner>125.095000 -37.527500</ows:LowerCorner>
                <ows:UpperCorner>153.637500 -10.020000</ows:UpperCorner>
            </ows:WGS84BoundingBox>
        </FeatureType>
        <FeatureType>
            <Name>deltares:full_extent_cta</Name>
            <Title>SFINCS full extent (not clean)</Title>
            <DefaultCRS>urn:ogc:def:crs:EPSG::4326</DefaultCRS>
            <OtherCRS>urn:ogc:def:crs:EPSG::4326</OtherCRS>
            <OtherCRS>urn:ogc:def:crs:EPSG::3857</OtherCRS>
            <ows:WGS84BoundingBox>
                <ows:LowerCorner>125.095000 -37.527500</ows:LowerCorner>
                <ows:UpperCorner>153.637500 -10.020000</ows:UpperCorner>
            </ows:WGS84BoundingBox>
        </FeatureType>
    </FeatureTypeList>
</WFS_Capabilities>

Note: in this example a Deltares namespace is used to identify items that originate from Delft-FEWS, as identified by xmlns:deltares="http://deltares.nl". This is used as prefix for the gridplot-id values that have been taken from the spatial display configuration, The WFS standard more or less requires this. The namespace used by the WFS service can be changed in the Webservices.xml configuration.

GetFeature

Get the polygon GridPlot vector data in GML or GeoJSON format, the GridPlot to get is specified by the FeatureTypes parameter.

Request parameters

  • typeNames (required): the gridPlot id of the plot to display. Only one gridPlot id is supported.
  • version (optional): supported version is 2.0 and is the default if not set. Older versions are not supported
  • crs (optional): the output projection of the plot. The default projection used by FEWS is always EPSG:4326 (unprojected WGS84 longitude, latitude) Other projections are supported only if they are configured in webservices.,xml. 
  • bbox (optional): the bounding box (in the projection as defined by the CRS parameter) of the extent of interest. Features that completely lie outside the BBOX area will not be returned.
  • filter (optional): a filter expression in encoded xml format as specified in the OpenGIS Filter Encoding 2.0 Encoding Standard, only the "Minimum Standard Filter" conformance class is currently implemented and has been tested.
    for more information see the section about filtering below.
  • format (optional, 'application/gml+xml; version=3.2' is the default): GML is the standard output format any WFS implementation must support, optionally 'application/geo json'  can be requested, which is more compact and generally easier to process..

Vendor specific request parameters

  • time (optional): the time for which the polygon data is requested. Only one time is supported. Time ranges are NOT supported. Time has to be in the xml dateformat:  yyyy-MM-ddTHH:mm:ssZ. The time parameter is identical to that of the Delft-FEWS WMS service for practical reasons. If no time parameter is specified, the most recent (current) forecast data will be returned.
    Please note that any options the OpenGIS Filter specifications offer to define a temporal extent have not been implemented in Delft-FEWS WFS at this moment.
  • cql_filter (optional): similar to the filter parameter, a filter expression in CQL (Common Query Language) syntax can be specified to request only a subset of features. This syntax is easier to use than the XML filter syntax, for more information see the section about filtering below.

Restrictions:

  • There currently are no restrictions on the output size of the WFS service, paging options that may help dealing with very large datasets have not yet been implemented.

Response

GML 3 or GeoJSON vector data of the requested polygon gridPlot for the specified time. if no time is specified the last available timestep will be returned.

Example request

http://localhost:8080/FewsWebServices/wfs?service=wfs&request=GetFeature&typenames=r-1_shapeFWA

Example response:

The typical response in GML or GeoJSON for polygon date is too large to be displayed here.

DescribeFeatureType

Provides a detailed description of one or more feature types, the most important function of this request is to list the available feature attributes (FEWS timeseries properties). The output format is a XML schema.

Request parameters

  • typeNames (required): the gridPlot id of one or more plots to display. if this is not specified a list of feature types is provided as a list of uri's
  • version (optional): supported version is 2.0 and is the default if not set. Older versions are not supported.

Example request

http://localhost:8080/FewsWebServices/wfs?service=wfs&request=DescribeFeatureType=r-1_shapeFWA&TypeNames=deltares:r-1_shapeFWA

Example response:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:gml="http://www.opengis.net/gml/3.2" xmlns:wfs="http://www.opengis.net/wfs/2.0" xmlns:deltares="http://deltares.nl" targetNamespace="http://deltares.nl">
    <xsd:import namespace="http://www.opengis.net/gml/3.2" schemaLocation="http://schemas.opengis.net/gml/3.2.1/gml.xsd"/>
    <xsd:complexType name="r-1_shapeFWAType">
        <xsd:complexContent>
            <xsd:extension base="gml:AbstractFeatureType">
                <xsd:sequence>
                    <xsd:element minOccurs="0" name="geometry" nillable="true" type="gml:MultiGeometryPropertyType"/>
                    <xsd:element minOccurs="0" name="model_type" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="model_reg" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="model_id" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="model_name" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="issue_freq" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="t_issue" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="t_step_int" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="variable" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="prod_type" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="t_start" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="t_end" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="t_length" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="bom_region" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="current" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="expired" nillable="true" type="xsd:string"/>
                    <xsd:element minOccurs="0" name="remarks" nillable="true" type="xsd:string"/>
                </xsd:sequence>
            </xsd:extension>
        </xsd:complexContent>
    </xsd:complexType>
    <xsd:element name="r-1_shapeFWA" substitutionGroup="gml:AbstractFeature" type="deltares:r-1_shapeFWAType"/>
</xsd:schema>


ListStoredQueries

Get a list of 'stored queries' a WFS supports, in this case the only stored query supported is the so-called "GetFeatureById" stored query. This request has been implemented as the WFS 2.0 lists it as a requirement for the "Simple" implementation of a WFS 2.0 service. Note: The id's, used mainly for the generation of GML output, are assigned sequentially, they are not linked to a specific property or attribute in Delft-FEWS.

Request parameters

  • version (optional): supported version is 2.0 and is the default if not set. Older versions are not supported

Example request

http://localhost:8080/FewsWebServices/wfs?service=wfs&request=ListStoredQueries

Example response:

<?xml version="1.0" encoding="UTF-8"?>
<ListStoredQueriesResponse  xmlns="http://www.opengis.net/wfs/2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wfs/2.0 http://schemas.opengis.net/wfs/2.0.0/wfs.xsd">
    <StoredQuery id="urn:ogc:def:query:OGC-WFS::GetFeatureById">
        <Title>Get feature by identifier</Title>
    </StoredQuery>
</ListStoredQueriesResponse >


DescribeStoredQueries

Get a more detailed description of 'stored queries' a WFS supports, in this case the only stored query supported is the so-called "GetFeatureById" stored query. This request has been implemented as the WFS 2.0 lists it as a requirement for the "Simple" implementation of a WFS 2.0 service. Note: The id's, used mainly for the generation of GML output, are assigned sequentially, they are not linked to a specific property or attribute in Delft-FEWS.

Request parameters

  • version (optional): supported version is 2.0 and is the default if not set. Older versions are not supported

Example request

http://localhost:8080/FewsWebServices/wfs?service=wfs&request=DescribeStoredQueries

Example response:

<?xml version="1.0" encoding="UTF-8"?>
<DescribeStoredQueriesResponse  xmlns="http://www.opengis.net/wfs/2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wfs/2.0 http://schemas.opengis.net/wfs/2.0.0/wfs.xsd">
    <StoredQueryDescription id="urn:ogc:def:query:OGC-WFS::GetFeatureById">
        <Title>Get feature by identifier</Title>
        <Parameter name="id" type="xs:string"/>
        <QueryExpressionText isPrivate="false" language="urn:ogc:def:queryLanguage:OGC-WFS::WFS_QueryExpression" returnFeatureTypes=""/>
    </StoredQueryDescription>
</DescribeStoredQueriesResponse>


WFS Request filtering

An important feature of the GetFeature request is filtering, which allows a subset of a feature set to be requested based on the feature properties/attributes, spatial extent or time. The filtering parameters that can be applied are;

  • time
  • bbox
  • filter
  • cql_filter

Time

The filtering using the TIME parameter works the same was as it does for the FEWS WMS service, a time parameter can be given on the request url in the format yyyy-MM-ddTHH:mm:ssZ 

Polygon based plots in the FEWS spatial display configuration typically are timeseries of polygons, so by using the TIME parameter you can request the polygons that are in the datastore for a specific timestep. If no TIME parameter is specified the most recent timestep will be returned. It currently is not possible to request a timeseries of polygons in a single request, a separate request for each timestep in a timeseries would be required.

BBOX

The BBOX (Bounding box) filter also works the same way as it does for the WMS service, by specifying a rectangular area in the form BBOX=<minX>,<minY>,<maxX>,<maxY> you can request only the features that partially or completely overlap that rectangular area. If a CRS parameter is provided to the GetFeature request to request the data in a specific cartographic projection, the bounding box coordinates should also be provided in that projection.

Filter

The standard FILTER parameter which is part of the official OpenGIS WFS 2.0 specification uses a XML based syntax, which has been documented in a separate document, OpenGIS Filter Encoding 2.0 Encoding Standard.

Only the "Minimum Standard Filter" conformance class is currently implemented, which means that the logical operators PropertyIsEqualTo, PropertyIsNotEqualTo, PropertyIsLessThan, PropertyIsGreaterThan,
PropertyIsLessThanOrEqualTo and PropertyIsGreaterThanOrEqualTo can be used and chained together using And / Or operators.

Now the problem with the standard XML based filter syntax is that the FEWS WFS implementation at this point only supports http GET methods, where all request parameters need to be passed on on the request url using NVP (Name-Value pair) syntax, and the XML for the filter parameter needs to be 'URL encoded"

To give an example, a project where the polygons have a property 'region_id' one could specify a filter for the WFS getFeature request in XML like like this:

<Filter>
  <PropertyIsEqualTo>
    <PropertyName>region-id</PropertyName>
    <Literal>123</Literal>
  </PropertyIsEqualTo>
</Filter>

Now this would need to be put on a single line and 'URL encoded' to get the FILTER parameter:

FILTER=%3CFilter%3E%3CPropertyIsEqualTo%3E%3CPropertyName%3Eregion_id%3C%2FPropertyName%3E%3CLiteral%3123%3C%2FLiteral%3E%3C%2FPropertyIsEqualTo%3E%3C%2FFilter%3E

This syntax is more or less unusable for manually putting together or interpreting WFS requests using filters, fortunately the CQL_FILTER parameter syntax is more practical.

CQL_Filter

The CQL_Filter parameter uses the Common Query Language format, which was developed by the OGC consortium as part of the Catalogue Service for the Web specification (CSW) and is for example implemented by Geoserver which is commonly considered the reference implementation of the WFS protocol. So the CQL_Filter parameter for the GetFeature request is not part of the official standard specifications, but strongly recommended for use in http GET requests,

The filter that was used as an example in the previous section in CQL syntax looks like this:

CQL_FILTER=region_id='123'

Multiple logical operators can be grouped together using AND / OR like this:

CQL_FILTER=region_id='123'+OR+region_id='124'


A nice overview of the CQL syntax is provided in the Geoserver documentation, however a warning is in place that not all possible filters mentioned there are currently supported and only the simple logical operators like in the above example have been tested at this point.

Properties

The following WFS specific properties can be configured in the webservices.xml configuration:

<Work in progress>


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