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WFS Filter Encoding

Author:Jeff McKenna
Contact:jmckenna at gatewaygeomatics.com
Author:Yewondwossen Assefa
Contact:assefa at dmsolutions.ca
Last Updated:2010-10-07
Date:$Date$

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.

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)

Units of measure

The following units of measure are supported:

m or meters meters
km or kilometers kilometers
NM nauticalmiles
mi or miles miles
in or inches inches
ft or feet feet
deg or dd degree
px pixels

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 (note the “Filter_Capabilities” section):

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<?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://schemas.opengis.net/wfs/1.0.0/WFS-capabilities.xsd">

<!-- MapServer version 5.6.5 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP
     OUTPUT=SWF OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE
     SUPPORTS=ICONV SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT
     SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT SUPPORTS=WCS_SERVER
     SUPPORTS=GEOS SUPPORTS=RGBA_PNG INPUT=EPPL7 INPUT=POSTGIS INPUT=OGR
     INPUT=GDAL INPUT=SHAPEFILE -->

<Service>
  <Name>MapServer WFS</Name>
  <Title>WMS Demo Server for MapServer</Title>
  <Abstract>This demonstration server showcases MapServer (www.mapserver.org)
            and its OGC support</Abstract>
  <OnlineResource>http://demo.mapserver.org/cgi-bin/wfs?</OnlineResource>
</Service>

<Capability>
  <Request>
    <GetCapabilities>
      <DCPType>
        <HTTP>
          <Get onlineResource="http://demo.mapserver.org/cgi-bin/wfs?"/>
        </HTTP>
      </DCPType>
      <DCPType>
        <HTTP>
          <Post onlineResource="http://demo.mapserver.org/cgi-bin/wfs?"/>
        </HTTP>
      </DCPType>
    </GetCapabilities>
    ...
  </Request>
</Capability>
...
<ogc:Filter_Capabilities>
  <ogc:Spatial_Capabilities>
    <ogc:Spatial_Operators>
      <ogc:Equals/>
      <ogc:Disjoint/>
      <ogc:Touches/>
      <ogc:Within/>
      <ogc:Overlaps/>
      <ogc:Crosses/>
      <ogc:Intersects/>
      <ogc:Contains/>
      <ogc:DWithin/>
      <ogc:BBOX/>
    </ogc:Spatial_Operators>
  </ogc:Spatial_Capabilities>
  <ogc:Scalar_Capabilities>
    <ogc:Logical_Operators/>
    <ogc:Comparison_Operators>
      <ogc:Simple_Comparisons/>
      <ogc:Like/>
      <ogc:Between/>
    </ogc:Comparison_Operators>
  </ogc:Scalar_Capabilities>
</ogc: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 "cities"
  TYPE POINT
  STATUS ON
  CONNECTION "http://demo.mapserver.org/cgi-bin/wfs?"
  CONNECTIONTYPE WFS
  METADATA
    "wfs_typename" "cities"
    "wfs_version" "1.0.0"
    "wfs_connectiontimeout" "60"
    "wfs_maxfeatures" "100"
    "wfs_filter" "<PropertyIsGreaterThan><PropertyName>POPULATION</PropertyName>
                  <Literal>10000000</Literal></PropertyIsGreaterThan>"
  END
  PROJECTION
    "init=epsg:4326"
  END
  LABELITEM    'NAME'
  CLASS
    NAME       'World Cities'
    STYLE
      COLOR    255 128 128
      OUTLINECOLOR 128 0 0
      SYMBOL   'circle'
      SIZE     9
    END
    LABEL
      COLOR    0 0 0
      OUTLINECOLOR 255 255 255
      TYPE     TRUETYPE
      FONT     sans
      SIZE     7
      POSITION UC
      PARTIALS FALSE
    END
  END
END

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:

http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsEqualTo><PropertyName>NAME</PropertyName>
  <Literal>Halifax</Literal></PropertyIsEqualTo></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsNotEqualTo><PropertyName>NAME</PropertyName>
  <Literal>Halifax</Literal></PropertyIsNotEqualTo></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsLessThan><PropertyName>POPULATION</PropertyName>
  <Literal>1000</Literal></PropertyIsLessThan></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsGreaterThan><PropertyName>POPULATION</PropertyName>
  <Literal>10000000</Literal></PropertyIsGreaterThan></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsLessThanOrEqualTo><PropertyName>POPULATION</PropertyName>
  <Literal>499</Literal></PropertyIsLessThanOrEqualTo></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsGreaterThanOrEqualTo><PropertyName>POPULATION</PropertyName>
  <Literal>10194978</Literal></PropertyIsGreaterThanOrEqualTo></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsBetween><PropertyName>POPULATION</PropertyName>
  <LowerBoundary>10194978</LowerBoundary>
  <UpperBoundary>12116379</UpperBoundary></PropertyIsBetween></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <PropertyIsLike wildcard='*' singleChar='.' escape='!'>
  <PropertyName>NAME</PropertyName><Literal>Syd*</Literal></PropertyIsLike>
  </Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <OR><PropertyIsEqualTo><PropertyName>NAME</PropertyName>
  <Literal>Sydney</Literal></PropertyIsEqualTo><PropertyIsEqualTo>
  <PropertyName>NAME</PropertyName><Literal>Halifax</Literal>
  </PropertyIsEqualTo></OR></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <AND><PropertyIsLike wildcard='*' singleChar='.' escape='!'>
  <PropertyName>NAME</PropertyName><Literal>Syd*</Literal></PropertyIsLike>
  <PropertyIsEqualTo><PropertyName>POPULATION</PropertyName>
  <Literal>4250065</Literal></PropertyIsEqualTo></AND></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <AND><NOT><PropertyIsEqualTo><PropertyName>POPULATION</PropertyName>
  <Literal>0</Literal></PropertyIsEqualTo></NOT><NOT><PropertyIsEqualTo>
  <PropertyName>POPULATION</PropertyName><Literal>12116379</Literal>
  </PropertyIsEqualTo></NOT></AND></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <BBOX><PropertyName>Name>NAME</PropertyName><Box%20srsName='EPSG:42304'>
  <coordinates>135.2239,34.4879 135.8578,34.8471</coordinates></Box></BBOX>
  </Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <DWithin><PropertyName>Geometry</PropertyName><gml:Point>
  <gml:coordinates>135.500000,34.666667</gml:coordinates>
  </gml:Point><Distance units='m'>10000</Distance></DWithin></Filter>
http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS
  &REQUEST=GetFeature&TYPENAME=cities&Filter=<Filter>
  <Intersects><PropertyName>Geometry</PropertyName>
  <gml:Polygon><gml:outerBoundaryIs><gml:LinearRing>
  <gml:coordinates>135.5329,34.6624 135.4921,34.8153 135.3673,34.7815
  135.3800,34.6216 135.5361,34.6210 135.5329,34.6624</gml:coordinates>
  </gml:LinearRing></gml:outerBoundaryIs></gml:Polygon></Intersects></Filter>

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.