[mapserver-dev] WFS 1.0.0 support in MapServer

Daniel Morissette morissette at dmsolutions.ca
Wed Oct 9 16:12:47 EDT 2002


I have committed to the MapServer CVS a first version of OGC WFS 1.0.0
server and client support.  There is still some work and testing to do
before it can be called complete, but if anyone feels brave then you can
start playing with it (experienced users only, please!).

The current implementation is complete enough for a MapServer
application to be able to render WFS layers from a remote MapServer WFS
server, including attribute classification, etc... really cool!  I'm
still working on supporting queries on WFS layers, and proper projection
support at both client and server ends (for now limit yourselves to
mapfiles and WFS layers in the same projection).

I attached to this message Draft documentation for what will eventually
become the WFS server and WFS client HOWTOs... it should contain enough
information for experienced users to get started with WFS.

Finally, I haven't been able to find any working WFS client or server on
the net to use in validating the MapServer implementation of the
protocol.  All I found were either incomplete prototypes or broken
pages.  So if anyone knows of a publicly available and functional WFS
1.0 client and/or server that we could use for testing then please let
us know.

 Daniel Morissette               morissette at dmsolutions.ca
 DM Solutions Group              http://www.dmsolutions.ca/
  Don't put for tomorrow what you can do today, because if 
      you enjoy it today you can do it again tomorrow.
-------------- next part --------------
MapServer WFS Server HOWTO

Support for serving OGC Web Feature Service (WFS) version 1.0.0 requests 
has been added to MapServer in version 3.7.  This allows remote clients
to connect to a MapServer instance via a standard protocol and access 
vector features in GML format.

The current implementation is a "Basic WFS" as defined in the specification.
This means that it provides only read-only access to the data but does not
support transaction requests.  
The WFS requests supported are  GetCapabilities, DescribeFeatureType and

A copy of the WFS 1.0.0 specification can be downloaded from:

Special Build considerations:

WFS support requires PROJ4, GDAL/OGR and libwww support libraries.
Build/install the above libraries on your system and then build MapServer
with the '--with-wfs --with-proj --with-ogr' configure options.  

Setting up a mapfile to serve WFS layers:

MapServer will serve and include in its WFS capabilities only the 
layers that meet the following conditions:

 - Data source is of vector type (Shapefile, OGR, PostGIS, SDE, SDO, ...)
 - LAYER NAME must be set
 - LAYER DUMP parameter set to TRUE

The following Metadata can be added to your mapfile, most of them are 

** MAP object Metadata **

- wfs_onlineresource

- wfs_title

- wfs_abstract

- wfs_keywordlist

- wfs_accessconstraints

- wfs_fees

- wfs_encoding
    Optional XML encoding for all XML documents returned by the server. 
    The default is ISO-8859-1.

- wfs_schemas_location
    Root of the web tree where the family of OGC WFS XMLSchema files are 
    located.  This must be a valid URL where the actual .xsd files are 
    located if you want your WFS output to validate in a validating XML
    The default if this is not set is to use "../" as the schema files 
    location, which should correspond to the root of your web server if you
    installed mapserv in the cgi-bin directory.
    See http://ogc.dmsolutions.ca/ for an example of a valid schema tree.

- wfs_geometry_element_name
    Name of the element (i.e. attribute) to use for the geometry in GML 
    output.  If not set then "MS_GEOMETRY" will be used.
    The layer-level "wfs_geometry_element_name" takes precedence over this

- wfs_srs
    ... still being defined.

** LAYER object Metadata **

- wfs_title

- wfs_abstract

- wfs_keywordlist

- wfs_geometry_element_name
    Name of the element (i.e. attribute) to use for the geometry in GML 
    output.  If not set then "MS_GEOMETRY" will be used.
    This value takes precedence over the value of "wfs_geometry_element_name"
    set at the map level (if one was set).

- wfs_srs
    ... still being defined.  Should be the SRS in which this layer 
    should be served.  Contrary to WMS servers, a WFS layer can be served
    in only one SRS.

Testing your WFS server:

The first thing to test is to issue a GetCapabilities request to your
server and scan the XML output to look for <!-- WARNING: ... --> comments.
Then take actions to fix every warning that you encounter.  At the end
of this you should have a compliant WFS server.

To issue a GetCapabilities request to your WFS server, enter a URL like 
the following in a web browser:


TODO, Known limitations:

** Before 3.7 release **

- Projection support still incomplete

- Need to validate request results against the corresponding XMLSchema

- It would be nice to test against multiple WFS clients before the 3.7
  release if possible... for now we can only test against the MapServer
  WFS client.

** Longer term TODO and limitations **

- This is just a basic WFS (read-only): transaction requests are not
  supported and probably never will given the nature of MapServer.

- For now we support only GET requests.  
  The spec also talks about XML-encoded POST requests but we do not 
  support that.

- We support only the BBOX filter for now.  It would be nice to support
  attribute filters, but this means supporting the OGC Filter Encoding spec
  and we'll keep that for later.

- WFS spec. seems to require that features of a given feature type must
  all be of the same geometry type (point, line, polygon).  This works fine
  for shapefiles, but some data source formats supported by MapServer allow
  mixed geometry types in a single layer and this goes against the WFS
  spec.  Suggestions on how to handle this are welcome.

-------------- next part --------------
MapServer WFS Client HOWTO:

Client support for OGC Web Feature Service (WFS) version 1.0.0 has been
added to MapServer in version 3.7.  This allows users to include 
references to WFS layers in their MapServer maps, and MapServer will 
handle them in a transparent manner.

A copy of the WFS 1.0.0 specification can be downloaded from:

Special Build considerations:

WFS client requires OGR with GML support, which in turn requires the 
Xerces-C++ 1.6.0 library:

1- Download xerces-c-src1_6_0.tar.gz from

2- Extract the archive and follow the build/install instructions in 

   On regular Linux systems, this should come back to:

     export XERCESCROOT=/path/to/xerces-c-src1_6_0
     chmod +x ./configure   <-- The file in the distribution is not executable!
     sudo make install
     sudo /sbin/lcdonfig

3- Build/install GDAL/OGR, making sure you include the '--with-xerces'
   configure option

4- Compile MapServer with the '--with-wfsclient' configure option.

Setting up a WFS layer in your mapfile:

A WFS layer is a regular mapfile layer, which can use CLASS objects, with
expressions, etc.  Instead of a DATA parameter, your use the CONNECTIONTYPE
and CONNECTION parameters to define the data source:


    # Like any other layers, WFS layers need a NAME and TYPE value
    name "mylayer"

    # Define the WFS connection parameters
    # The CONNECTION must include the following WFS GetFeature parameters:
    #  SERVICE=WFS  
    #  VERSION=1.0.0  (the only version supported for now)
    #  TYPENAME=...   (the feature type for this layer, see WFS capabilites)
    CONNECTION "http://my.wfs.com/cgi-bin/mapserv?map=mywfs.map&SERVICE=WFS&VERSION=1.0.0&TYPENAME=mypoints"

    # projection is optional, like for most layer types in MapServer

    # Optional Metadata items
      "wfs_connectiontimeout" "60"              # Default is 30 seconds
      "wfs_latlonboundingbox" "-75 45 -70 50"   # Area covered by this layer

    # Define some classes, to render the features
    CLASSITEM "point_class"
      EXPRESSION "1"
      SYMBOL 'triangle'
      COLOR 255 0 0
      SYMBOL 'circle'
      COLOR 0 0 0


You also need to set the IMAGEPATH value in your mapfile since MapServer
uses this directory to store temporary files downloaded from the remote
WFS server:


      IMAGEPATH "/tmp/ms_tmp/"
      IMAGEURL ...

TODO, Known limitations:

** Before 3.7 release **
- Queries not supported yet, still working on this.  For now you can 
  only render maps but cannot query using WFS layers.

- Projection support incomplete.  If you use projections then make sure the
  layer's PROJECTION object in the mapfile is set to the same projection
  as the SRS supported for this TYPENAME in the remote WFS server.

** Longer term TODO and limitations **

- Need some caching mechanism to avoid downloading the same data multiple
  times if the BBOX of the map doesn't change.

- Temporary WFS (gml) files are written to the IMAGEPATH directory, but 
  this could become a security concern since it makes the raw GML data 
  downloadable by someone who could guess the gml filename.  We should
  consider having a "wfs_tmpdir" metadata that, if it is set will define
  a directory where temp files should be written.  The default would still
  be to use the value of IMAGEPATH if "wfs_tmpdir" is not set.
- Xerces is an annoying dependency for GML support in OGR.  There have
  been discussions about modifying the OGR GML driver to use in internal
  XML parser by default.  This would save us from the Xerces dependency.
  There is no formal plan for when this would happen yet.

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