184 lines
No EOL
6.4 KiB
Text
184 lines
No EOL
6.4 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 Mapnik C++
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library.
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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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Features
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--------
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- WMS 1.1.1 and 1.3.0
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- CGI/FastCGI, WSGI, mod_python
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- Supports all 3 requests: GetCapabilities, GetMap and GetFeatureInfo
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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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- Ability to request all layers with LAYERS=__all__
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Caveats
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----------------
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- GetFeatureInfo supports text/plain output only
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- PNG256(8-bit PNG not yet supported)
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- CGI/FastCGI interface needs to be able to write to tempfile.gettempdir() (most likely "/tmp")
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- Need to be further evaluated for thread safety
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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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- Mapnik python bindings (which will also install the `ogcserver` module code)
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- lxml (http://codespeak.net/lxml/)
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- PIL (http://www.pythonware.com/products/pil)
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For the CGI/FastCGI interface also install:
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- jonpy (http://jonpy.sourceforge.net/)
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Installation
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------------
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- The OGCServer uses the Mapnik interface to the Proj.4 library for projection support
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and depends on integer EPSG codes. Confirm that you have installed Proj.4 with
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all necessary data files (http://trac.osgeo.org/proj/wiki/FAQ) and have added any custom
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projections you need to the 'epsg' file usually located at '/usr/local/share/proj/epsg'.
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- Test that the server code is available and installed properly by importing it within a
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python interpreter::
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>>> from mapnik import ogcserver
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>>> # no error means proper installation
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- There is a sample python script called "wms.py" in the utils/ogcserver folder of the
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Mapnik source code that will work for both CGI and FastCGI operations. Where to place it
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will depend on your server choice and configuration and is beyond this documentation.
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For information on FastCGI 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 create two simple python scripts:
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1) The web-accessible python script ('wms.py') which will import the
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ogcserver module code and associate itself with the 'ogcserver.conf'
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configuration file. The code of this script will depend upon whether
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you deploy the server as cgi/fastcgi/wsgi/mod_python. See the Mapnik
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Community Wiki for examples: http://trac.mapnik.org/wiki/OgcServer and
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see the cgi sample in the /utils/ogcserver folder.
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2) A 'map_factory' script which loads your layers and styles. Samples of this
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script can be found below.
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- Next you need to edit the ogcserver.conf file to:
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1) Point to the 'map_factory' script by using the "module" parameter
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2) Fill out further settings for the server.
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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
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--------------------------
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The ogcserver obviously needs layers to publish and styles for how to display those layers.
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You create you layers and styles in the 'map_factory' script.
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For now this can be done by either loading an XML mapfile inside that script using the
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'loadXML()' function or by writing your layers and styles in python code, or both.
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The 'map_factory' module must look, at a bare minimum like if you load layers and styles
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using an existing XML mapfile::
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from mapnik.ogcserver.WMS import BaseWMSFactory
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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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self.loadXMl('/full/path/to/mapfile.xml')
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self.finalize()
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Or if you want to define your layers and styles in pure python dynamically you might
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have a 'map_factory' more like::
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from mapnik.ogcserver.WMS import BaseWMSFactory
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from mapnik import *
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SHAPEFILE = '/path/to/world_borders.shp'
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PROJ4_STRING = '+init=epsg:4326'
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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,rl = Style(),Rule()
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poly = PolygonSymbolizer(Color('#f2eff9'))
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line = LineSymbolizer(Color('steelblue'),.1)
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rl.symbols.extend([poly,line])
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sty.rules.append(rl)
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self.register_style('world_style',sty)
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lyr = Layer('world',PROJ4_STRING)
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lyr.datasource = Shapefile(file=SHAPEFILE)
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lyr.title = 'World Borders'
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lyr.abstract = 'Country Borders of the World'
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self.register_layer(lyr,'world_style',('world_style',))
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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 of 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 have registered everything! This will
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validate everything and let you know if there are any problems.
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- For a layer to be queryable via GetFeatureInfo, simply set the 'queryable'
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property to True::
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lyr.queryable = True
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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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- 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. |