141 lines
4.4 KiB
Text
141 lines
4.4 KiB
Text
# $Id$
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Mapnik OGC Server
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-----------------
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Introduction
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------------
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Mapnik provides a server package to allow the publishing of maps
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through the open and standard WMS interface published by the Open Geospatial
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Consortium (OGC). It is in implemented in Python, around the core C++
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library.
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Features/Caveats
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----------------
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- WMS 1.1.1 and 1.3.0
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- CGI/FastCGI
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- GetCapabilities and GetMap support only (NO GetFeatureInfo ... yet)
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- JPEG/PNG output
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- XML/INIMAGE/BLANK error handling
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- Multiple named styles support
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- Reprojection support
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- Supported layer metadata: title, abstract
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- Needs to be able to write to tempfile.gettempdir() (most likely "/tmp")
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Dependencies
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------------
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Please properly install the following before proceeding further:
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- jonpy (http://jonpy.sourceforge.net/)
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- lxml (http://codespeak.net/lxml/)
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- PIL (http://www.pythonware.com/products/pil)
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- PROJ.4 (http://proj.maptools.org/)
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Installation
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------------
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- Make sure Mapnik was compiled and linked with PROJ.4 support. If this isn't
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the case, recompile Mapnik and make sure it is.
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- The executable "ogcserver" in utils/ogcserver will work for both CGI and
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FastCGI operations. Where to place it will depend on your server's
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configuration and is beyond this documentation. For information on FastCGI
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go to http://www.fastcgi.com/.
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Configuring the server
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----------------------
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- You will need to edit the ogcserver executable for now. It is a simple
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Python text script.
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1) Edit the path to the interpreter in the first line.
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2) Edit the path to the config file if you don't like the default.
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- Copy the sample configuration "ogcserver.conf" file in utils/ogcserver to
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the location you specified in the previous step.
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- Edit the configuration file to your liking, the comments within the file will
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help you further. Be sure to at the very minimum edit the "module"
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parameter, the server will not work without you setting it properly first.
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Defining layers and styles for use by the ogcserver
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---------------------------------------------------
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The ogcserver obviously needs layers to publish. For now, with Mapnik, this
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can only be done by writing code. In this case, a Python script will need to be
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written to describe the layers and respective styles. For information on the Python
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API, look in demo/python, or in docs/epydocs.
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The server needs a python module, with code that looks like this:
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from mapnik.ogcserver.WMS import BaseWMSFactory
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from mapnik import Layer, Style
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class WMSFactory(BaseWMSFactory):
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def __init__(self):
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BaseWMSFactory.__init__(self)
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sty = Style()
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...
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self.register_style('stylename', sty)
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lyr = Layer('layername', '+init=epsg:4326')
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lyr.title = 'Layer title'
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lyr.abstract = 'Layer abstract'
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...
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self.register_layer(lyr, 'stylename')
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self.finalize()
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The rules for writing this class are:
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- It MUST be called 'WMSFactory'.
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- It MUST sub-class mapnik.ogcserver.WMS.BaseWMSFactory.
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- The __init__ MUST call the base class'.
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- Layers MUST be named with the first parameter to the constructor.
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- Layers MUST define an EPSG projection in the second parameter to the
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constructor. This implies that the underlying data must be in an EPSG
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projection already.
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- style and layer names are meant for machine readability, not human. Keep
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them short and simple, without spaces or special characters.
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- For human readable info, set the title and abstract properties on the layer
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object.
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- DO NOT register styles using layer.styles.append(), instead, provide style
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information to the register_layer() call:
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register_layer(layerobject, defaultstylename, tuple of alternative style names)
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- No Map() object is used or needed here.
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- Be sure to call self.finalize() once you've registered everything! This will
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validate everything and let you know if there's problems.
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To Do
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-----
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- Investigate moving to cElementTree from lxml.
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- Add some internal "caching" for performance improvements.
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- Support GetFeatureInfo (Requires core changes).
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- Switch to using C/C++ libs for image generation, instead of PIL (also
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requires core changes). PIL requirement will remain for INIMAGE/BLANK
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error handling.
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Conclusion
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----------
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This is the very first implementation of a WMS for Mapnik. Although inital
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testing seems to suggest it works well, there may be bugs, and it lacks some
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useful features. Comments, contributions, and requests for help should all be
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directed to the Mapnik mailing list.
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Enjoy!
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J.F.
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