WFS Filter Encoding

Author:Jeff McKenna Contact:jmckenna at gatewaygeomatics.com Author:Yewondwossen Assefa Contact:assefa at dmsolutions.ca Revision:$Revision: 8479 $ Date:$Date: 2009-01-29 11:56:34 -0800 (Thu, 29 Jan 2009) $ Last Updated:2005/09/23

Table of Contents

• WFS Filter Encoding
  • Introduction
  • Currently Supported Features
  • Get and Post Requests
  • Use of Filter Encoding in MapServer
  • Limitations
  • Tests

Introduction

This document describes the procedures for taking advantage of the Filter Encoding (FE) support in WFS GetFeature requests, which was added to MapServer in version 4.2.

This document assumes that you are already familiar with the following aspects of MapServer:

• MapServer application development and setting up .map files.
• Familiarity with the WFS specification would be an asset. Links to the MapServer WFS documents are included in the next section.

Links to SLD-related Information

• Filter Encoding Implementation Specification.
• MapServer WFS Client Howto.
• MapServer WFS Server Howto.
• MapServer OGC Web Services Workshop.
• Open GIS Consortium (OGC) home page.

Currently Supported Features

The following table lists the currently supported features for FE.

Table 1. Currently Supported Features

Feature Set	Feature
Spatial Capabilities
	Equals
	Disjoint
	Touches
	Within
	Overlaps
	Crosses
	Intersects
	Contains
	DWithin
	BBOX
Scalar Capabilities
Logical Operators
	And
	Or
	Not
Comparison Operators
	PropertyIsEqualTo (=)
	PropertyIsNotEqualTo (<>)
	PropertyIsLessThan (<)
	PropertyIsGreaterThan (>)
	PropertyIsLessThanOrEqualTo (<=)
	PropertyIsGreaterThanOrEqualTo (>=)
	PropertyIsLike
	PropertyIsBetween (range)

Get and Post Requests

MapServer already has the capability to receive and parse Get requests and URL-encoded Post requests. The ability for MapServer to be able to receive Post requests with XML-encoded information sent in the body of the request has been added. Also, the ability to generate XML-encoded Post requests for WFS layers has been added.

Both Get and Post request are now supported for all WFS requests:

• GetCapabilities
• GetFeatures
• DescribeFeatureType

Supporting these WFS requests in Post was implemented to keep consistency between all supported WFS requests.

When sending requests, the default request method used is Post. To change this behavior, we have introduced a layer level meta data, wfs_request_method, which can be set to “GET”.

Use of Filter Encoding in MapServer

This section describes how to use FE on both the server and client sides.

Server Side

To be able to use Filter Encoding, you need to create a valid WFS server using MapServer. Please refer to the WFS Server HOWTO for specifics.

There is nothing special that should be added to a WFS server for Filter Encoding, but you should note that, when requesting the capabilities of your WFS server, the document returned should contain the supported filters. Here is part of a Capabilities document as well as the Post support:

<?xml version='1.0' encoding="ISO-8859-1" ?>
<WFS_Capabilities
   version="1.0.0"
   updateSequence="0"
   xmlns="http://www.opengis.net/wfs"
   xmlns:ogc="http://www.opengis.net/ogc"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://www.opengis.net/wfs http://ogc.dmsolutions.ca/wfs/1.0.0/WFS-capabilities.xsd">

<!-- MapServer version 4.1 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP
OUTPUT=PDF OUTPUT=SWF SUPPORTS=PROJ SUPPORTS=FREETYPE SUPPORTS=WMS_SERVER
SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT INPUT=POSTGIS
INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE -->

<Service>
  <Name>MapServer WFS</Name>
  <Title>GMap WMS Demo Server</Title>
  <OnlineResource>http://localhost/cgi-bin/mapserv.exe?map=
    c:/msapps/wfs_filter/htdocs/ns_wfsserver.map&</OnlineResource>
</Service>

<Capability>
  <Request>
    <GetCapabilities>
      <DCPType>
        <HTTP>
          <Get onlineResource="http://localhost/cgi-bin/mapserv.exe?map=
            c:/msapps/wfs_filter/htdocs/ns_wfsserver.map&" />
        </HTTP>
      </DCPType>
      <DCPType>
        <HTTP>
          <Post onlineResource="http://localhost/cgi-bin/mapserv.exe?map=
            c:/msapps/wfs_filter/htdocs/ns_wfsserver.map&" />
        </HTTP>
      </DCPType>
    </GetCapabilities>
    ...
  </Request>
</Capability>
...
<Filter_Capabilities>
  <Spatial_Capabilities>
    <Spatial_Operators>
             <Intersect/>
             <DWithin/>
           <BBOX/>
    </Spatial_Operators>
  </Spatial_Capabilities>
  <Scalar_Capabilities>
    <Logical_Operators />
    <Comparison_Operators>
      <Simple_Comparisons />
      <Like />
      <Between />
    </Comparison_Operators>
  </Scalar_Capabilities>
</Filter_Capabilities>

</WFS_Capabilities>

Client Side

To be able to generate a Filter to a WFS server, a layer level metadata called wfs_filter has been added, which should contain the filter to be sent to the server. Following is an example of a valid WFS client layer with a filter:

LAYER
  NAME popplace
  METADATA
    "wfs_version"   "1.0.0"
    "wfs_typename"  "popplace"
    "wfs_filter"    "<PropertyIsGreaterThan><PropertyName>POP_RANGE</PropertyName>
                                     <Literal>4</Literal></PropertyIsGreaterThan>"
  END
  TYPE POINT
  STATUS ON
  PROJECTION
    "init=epsg:42304"
  END
  CONNECTIONTYPE WFS
  CONNECTION "http://www2.dmsolutions.ca:8090/cgi-bin/mswfs_filter?"
  LabelItem "Name"
  CLASSITEM "Capital"
  CLASS
    SYMBOL 2
    SIZE 8
    NAME "Cities"
    LABEL
      COLOR  255 0 0
      FONT fritqat-italic
      TYPE truetype
      SIZE 8
      POSITION AUTO
      OUTLINECOLOR 255 255 255
      FORCE TRUE
    END
    COLOR 0 0 0
  END
END # Layer

Note:

• The filter given as a value of the wfs_filter metadata should not contain <Filter> start and end tags.
• The CONNECTION points to a valid WFS server supporting filters
• The returned shapes will be drawn using the class defined in the layer.

Limitations

• A limited set of spatial operators are supported.

Tests

Here are some test URLs for the different supported filters:

• PropertyIsEqualTo

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsEqualTo><PropertyName>NAME</PropertyName>
<Literal>Digby</Literal></PropertyIsEqualTo></Filter>

• PropertyIsNotEqualTo

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsNotEqualTo><PropertyName>NAME</PropertyName>
<Literal>Digby</Literal></PropertyIsNotEqualTo></Filter>

• PropertyIsLessThan

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsLessThan><PropertyName>POP_RANGE</PropertyName>
<Literal>2</Literal></PropertyIsLessThan></Filter>

• PropertyIsGreaterThan

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsGreaterThan><PropertyName>POP_RANGE</PropertyName>
<Literal>5</Literal></PropertyIsGreaterThan></Filter>

• PropertyIsLessThanOrEqualTo

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsLessThanOrEqualTo><PropertyName>POP_RANGE</PropertyName>
<Literal>2</Literal></PropertyIsLessThanOrEqualTo></Filter>

• PropertyIsGreaterThanOrEqualTo

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsGreaterThanOrEqualTo><PropertyName>POP_RANGE</PropertyName>
<Literal>5</Literal></PropertyIsGreaterThanOrEqualTo></Filter>

• PropertyIsBetween

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsBetween><PropertyName>POP_RANGE</PropertyName>
<LowerBoundary>5</LowerBoundary><UpperBoundary>6</UpperBoundary></PropertyIsBetween></Filter>

• PropertyIsLike

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><PropertyIsLike wildcard='*' singleChar='.' escape='!'>
<PropertyName>NAME</PropertyName><Literal>Syd*</Literal></PropertyIsLike></Filter>

• Logical operator OR

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><OR><PropertyIsEqualTo><PropertyName>NAME</PropertyName>
<Literal>Sydney</Literal></PropertyIsEqualTo><PropertyIsEqualTo><PropertyName>NAME</PropertyName>
<Literal>Digby</Literal></PropertyIsEqualTo></OR></Filter>

• Logical operator AND

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><AND><PropertyIsLike wildcard='*' singleChar='.' escape='!'>
<PropertyName>NAME</PropertyName><Literal>Syd*</Literal></PropertyIsLike><PropertyIsEqualTo>
<PropertyName>POP_RANGE</PropertyName><Literal>4</Literal></PropertyIsEqualTo></AND></Filter>

• Logical operator NOT

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&
TYPENAME=popplace&Filter=<Filter><AND><NOT><PropertyIsEqualTo><PropertyName>POP_RANGE</PropertyName>
<Literal>2</Literal></PropertyIsEqualTo></NOT><NOT><PropertyIsEqualTo><PropertyName>POP_RANGE</PropertyName>
<Literal>3</Literal></PropertyIsEqualTo></NOT></AND></Filter>

• Spatial operator BBOX

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&TYPENAME=popplace&
Filter=<Filter><BBOX><PropertyName>Name>NAME</PropertyName><Box%20srsName='EPSG:42304'>
<coordinates>2518000,150000 2918000,450000</coordinates></Box></BBOX></Filter>

• Spatial operator Dwithin

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&TYPENAME=popplace&Filter=
<Filter><DWithin><PropertyName>Geometry</PropertyName><gml:Point><gml:coordinates>2587598.000000,404010.531250</gml:coordinates>
</gml:Point><Distance units='m'>1000</Distance></DWithin></Filter>

• Spatial operator Intersects

http://www2.dmsolutions.ca/cgi-bin/mswfs_filter?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&TYPENAME=popplace&Filter=<Filter>
<Intersect><PropertyName>Geometry</PropertyName><gml:Polygon><gml:outerBoundaryIs><gml:LinearRing>
<gml:coordinates>2488789,289552 2588789,289552 2588789,389552 2488789,389552 2488789,289552</gml:coordinates>
</gml:LinearRing></gml:outerBoundaryIs></gml:Polygon></Intersect></Filter>

• Tests using MapServer as a WFS client and a WFS server are available at http://www2.dmsolutions.ca/msapps/wfs_fe/.
• The OGC conformance tests (http://cite.occamlab.com/tsOGC/) have been run on the FE support. The following table and notes reflect the current status.

Table 2. WFS OGC test suite (over the HTTP Get and Post method)

Test #	Description	# of Tests	# of Failed Tests
1	Basic WFS tests over the HTTP Get and Post method	402	281
1.1	GetCapabilities	16	0
1.2	DescribeFeatureType	18	0
1.3	GetFeature	368	281
1.3.1	Basic WFS tests	20	1
1.3.2	Complex WFS tests	18	18
1.3.3	Arithmetic filter WFS tests	8	8
1.3.4	Comparison WFS tests	50	26
1.3.4.1	GetFeature PropertyIsGreaterThanOrEqualTo filter	2	0
1.3.4.2	GetFeature PropertyIsBetween filter	6	2
1.3.4.3	GetFeature PropertyIsEqualTo filter	4	0
1.3.4.4	GetFeature PropertyIsGreaterThan filter	4	2
1.3.4.5	GetFeature PropertyIsGreaterThanOrEqualTo filter	6	6
1.3.4.6	GetFeature PropertyIsLessThan filter	6	4
1.3.4.7	GetFeature PropertyIsLessThanOrEqualTo filter	6	4
1.3.4.8	GetFeature PropertyIsLike filter	2	0
1.3.4.9	GetFeature PropertyIsNotEqualTo filter	6	0
1.3.4.10	GetFeature PropertyIsNull filter	8	8
1.3.5	Logical WFS test	20	0
1.3.5.1	GetFeature AND PropertyIsEqualTo PropertyIsEqualTo filter	8	0
1.3.5.2	GetFeature OR PropertyIsEqualTo PropertyIsEqualTo filter	8	0
1.3.5.3	GetFeature NOT PropertyIsNotEqualTo filter	4	0
1.3.6	Spatial operator WFS test	252	228
1.3.6.1	GetFeature BBOX filter	36	12
1.3.6.2	GetFeature with other filter types	216	216
2	Transactional WFS test	69	69

The OGC Cite WFS test suite can be found on the OGC Cite portal.

Following are some MapServer specific notes on this test suite:

1. Test number 1.3.1:

   • There is a contradiction between the wfs/1.0.0/basic/getfeature/post/3 assertion and the XPath expected value of the test. The assertion says: “Test that a GetFeature request with no output format defined returns a wfs:FeatureCollection with GML data.” and the expected XPath value for this request: “boolean(/ogc:ServiceExceptionReport)” is supposed to be true. So, the assertion means that when a WFS server receives a request which contains an undefined output format or no output format at all, the WFS server must return a WFS collection containing GML data. The XPath expected value means that when a WFS server receives a request with an undefined output format or no output format at all, the WFS server must return a service exception report.

2. Tests number 1.3.2 and 1.3.3:

   • Not supported.

3. Tests number 1.3.4.2, 1.3.4.4 to 1.3.4.7:

   • The string comparison is not supported using >, <, >=, <=.
   • The date comparison is not supported.

   See also

   bug 461

4. Test number 1.3.4.10:

   • This property is not supported in MapServer.

5. Test number 1.3.6.1:

   • The returned feature xml won’t validate because the validation is done against a specific xsd (geomatry.xsd).
   • The data conversion on multipoints and multilayers are not supported within GDAL.

   See also

   bug 461

6. Test number 2:

   • The transaction requests are not supported.