Mapnik's OGC Server

Overview

This page dicusses all things related to supporting OpenGeospatial Consortium (OGC) server related specifications in Mapnik.

As of 0.3.0, Mapnik provides an beta Web Mapping Service (WMS) compliant server, written in Python.

Features

Supports both versions 1.1.1 and 1.3.0 of the specification.

Supports all operations:

  • GetCapabilities
  • GetMap
  • GetFeatureInfo (As of 0.4.0)

Supports defining styles and layers in python and by loading an xml mapfile (as of 0.6.0)

It can be configured to be run within a webserver as either:

  • CGI
  • FastCGI
  • WSGI
  • mod_python (as of 0.6.0)

Or can be run as a local process using a wsgiref localserver

See below for Sample configurations

Dependencies

  • Python
  • Mapnik installed with Python Bindings
  • Proj4 epsg file with all needed customs projections added (ie. google mercator)
  • lxml (Optional as of 0.6.1 -if not present will fall back on built-in xml lib)
  • PIL (Python Imaging Library)
  • For running as CGI or FastCGI:

Installation

  • The server code is automatically installed in the Python site-packages folder along with the Mapnik Python bindings.
  • To test installation try importing the ogcserver module within a python interpreter: 
    >>> from mapnik import ogcserver
>>> # no error means proper installation
  • To test that your Proj4 'epsg' file can be located choose and EPSG code your server will be exposing, say EPSG 4326 (WGS 84) or EPSG 900913 (Google Mercator), try instantiating from the Mapnik python bindings: 
    >>> from mapnik import Projection
>>> Projection('+init=epsg:4326')
Projection('+init=epsg:4326')
>>> Projection('+init=epsg:900913')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: failed to initialize projection with:+init=epsg:900913
  • In this example 4236 was found, but 900913 needs to be manually added to the 'epsg' file usually located at /usr/share/proj/epsg. On Mac OS X if you installed the PROJ framework from KyngChaos Wiki the location will be at /Library/Frameworks/PROJ.framework/resources/proj. 
    <900913> +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs  <>

Setup

See the OgcServerSvn (Web-based view of the document available in the mapnik source code here)

Sample Configurations

Usually this file is named 'wms.py':

WSGI 

#!/usr/bin/env python

import sys
from mapnik.ogcserver.wsgi import WSGIApp
sys.path.append('/path/to/map_factory/')

application = WSGIApp('/path/to/ogcserver.conf')
  • To run the WSGI as a standalone server do: 
    # add these line to the bottom of your wsgi-based 'wms.py'

if __name__ == '__main__':
    from wsgiref.simple_server import make_server
    httpd = make_server('localhost', 8000, application)
    print "Listening on port 8000...."
    httpd.serve_forever()
  • And then do: 
    $ python wms.py
Listening on port 8000.... # go to http://localhost:8000 in your browser

CGI/FastCGI 

#!/usr/bin/env python

import sys
from mapnik.ogcserver.cgiserver import Handler
sys.path.append('/path/to/map_factory/')
from jon import fcgi

class OGCServerHandler(Handler):
    configpath = '/path/to/ogcserver.conf'

fcgi.Server({fcgi.FCGI_RESPONDER: OGCServerHandler}).run()

Mod Python

Note that the mod_python environment keeps Python code in memory, so after making changes to worldMapServer.py or other files, an Apache reload or restart may be required.

wms.py 

#!/usr/bin/env python

import sys
from mapnik.ogcserver.modserver import ModHandler
sys.path.append('/path/to/map_factory/')

handler = ModHandler('/path/to/ogcserver.conf')

Apache Configuration 

<Directory "/home/dane/projects/ogcserver/">
  PythonPath "['/home/dane/projects/ogcserver/'] + sys.path"
  AddHandler mod_python .py
  PythonHandler wms
</Directory>

Plans for the future

  • Test with various WMS clients
  • Add support for text/xml and text/html to GetFeatureInfo (only supports text/plain in 0.4.0)
  • Investigate WMS-C integration

History

For a bit of history on the server development see: http://lists.berlios.de/pipermail/mapnik-devel/2006-April/000011.html