| Home | Products | Issue Tracker | Service Providers | FAQ | Twitter | Download

# WFS Filter Encoding

Author

  Jeff McKenna

Contact

  jmckenna at gatewaygeomatics.com

Author

  Yewondwossen Assefa

Contact

  assefa at dmsolutions.ca

Last Updated

  2010-10-07

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.

As of MapServer 7.0, the OGC Filter Encoding 2.0 specification is also used to evaluate Filters of WFS 2.0 GetFeature requests.

### 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)

### 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):

     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61
    62
    63
    64
    65
    66
    <?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>https://demo.mapserver.org/cgi-bin/wfs?</OnlineResource>
    </Service>

    <Capability>
      <Request>
        <GetCapabilities>
          <DCPType>
            <HTTP>
              <Get onlineResource="https://demo.mapserver.org/cgi-bin/wfs?"/>
            </HTTP>
          </DCPType>
          <DCPType>
            <HTTP>
              <Post onlineResource="https://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 "https://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:

- PropertyIsEqualTo

    https://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>

- PropertyIsNotEqualTo

    https://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>

- PropertyIsLessThan

    https://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>

- PropertyIsGreaterThan

    https://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>

- PropertyIsLessThanOrEqualTo

    https://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>

- PropertyIsGreaterThanOrEqualTo

    https://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>

- PropertyIsBetween

    https://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>

- PropertyIsLike

    https://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>

- Logical operator OR

    https://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>

- Logical operator AND

    https://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>

- Logical operator NOT

    https://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>

- Spatial operator BBOX

    https://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>

- Spatial operator Dwithin

    https://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>

- Spatial operator Intersects

    https://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>

- The OGC conformance tests (http://cite.opengeospatial.org/test_engine) 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.