---------
TileCache
---------
TileCache is a BSD licensed tile caching mechanism. The goal is to make it
easy to set up a WMS or TMS frontend to any backend data services you might be
interested in, using a pluggable caching and rendering mechanism.
This implements the WMS-C server recommendation, as defined by
http://wiki.osgeo.org/index.php/WMS_Tiling_Client_Recommendation and the Tiled
Map Service specification, available at
http://wiki.osgeo.org/index.php/Tile_Map_Service_Specification
TileCache will run under Python CGI or mod_python.
Backend rendering can be powered by remote, or cascading, WMS requests, or by
MapServer rendering via python-mapscript. Support for other rendering engines
can be added with the implementation of a single function.
Caches can be maintained on disk, or via the memcached memory-based LRU caching
daemon.
TileCache was developed by MetaCarta Labs and released to the public under a
BSD license. For updates on tools released by MetaCarta Labs, you can subscribe
to the Labs Announce list, available at
http://labs.metacarta.com/mailman/listinfo/announce .
The TileCache was designed as a companion to OpenLayers, the BSD licensed web
mapping interface. For help with setting up TileCache for use with OpenLayers,
please feel free to stop by #openlayers, on irc.freenode.net, or to send email
to labs@metacarta.com.
To set up a TileCache under CGI
===============================
* Extract the code to some web directory (e.g. in /var/www).
* Edit tilecache.cfg to point the DiskCache to the location you wish
to cache tiles, and the layers to point to the map file or WMS
server you wish to cache
* Permit CGI execution in the TileCache directory.
For example, if TileCache is to be run with Apache, the
following must be added in your Apache configuration:
AddHandler cgi-script .cgi
Options +ExecCGI
where /var/www/tilecache is the directory resulting from
the code extraction.
* Visit:
http://example.com/yourdir/tilecache.cgi?LAYERS=basic&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&BBOX=-180,-90,0,90&WIDTH=256&HEIGHT=256
or:
http://example.com/yourdir/tilecache.cgi/1.0.0/basic/0/0/0.png
* If you see a tile you have set up your configuration correctly. Congrats!
Non-standard Python Location: If your Python is not at /usr/bin/python
on your system, you will need to change the first line of tilecache.cgi
to reference the location of your Python binary. A common example is:
#!/usr/local/bin/python
Under Apache, you might see an error message like:
[Wed Mar 14 19:55:30 2007] [error] [client 127.0.0.1] (2)No such file or
directory: exec of '/www/tilecache.cgi' failed
to indicate this problem.
You can typically locate where Python is installed on your system via the
command `which python`.
Windows users: If you are using Windows, you should change the first line
of tilecache.cgi to read:
#!C:/Python/python.exe -u
C:/Python should match the location Python is installed under on your
system. In Python 2.5, this location is C:/Python25 by default.
To set up a TileCache under mod_python
======================================
* Extract the code to some web directory (e.g. /var/www).
* Edit tilecache.cfg to point the DiskCache to the location you wish
to cache tiles, and the layers to point to the map file or WMS
server you wish to cache
* Add the following to your Apache configuration, under a heading:
AddHandler python-program .py
PythonHandler TileCache.Service
PythonOption TileCacheConfig /path/to/tilecache.cfg
An example might look like:
AddHandler python-program .py
PythonHandler TileCache.Service
PythonOption TileCacheConfig /var/www/tilecache/tilecache.cfg
where /var/www/tilecache is the directory resulting from
the code extraction.
* Visit one of the URLs described above, replacing tilecache.cgi with
tilecache.py
* If you see a tile you have set up your configuration correctly. Congrats!
To set up a TileCache under a standalone HTTP Server
====================================================
TileCache as of version 1.4 comes with a standalone HTTP server which uses
the WSGI handler. This implementation depends on Python Paste, which can be
downloaded from:
http://cheeseshop.python.org/pypi/Paste
For versions of Python earlier than 2.5, you will also need to install
wsgiref:
http://cheeseshop.python.org/pypi/wsgiref
Once you have all the prerequisites installed, simply run:
python tilecache_http_server.py
This will start a webserver listening on port 8080, after which you should
be able to open:
http://hostname:8080/1.0.0/basic/0/0/0.png
to see your first tile.
To set up a TileCache under FastCGI
===================================
TileCache as of version 1.4 comes with a fastcgi implementation. In
order to use this implementation, you will need to install flup, available
from:
http://trac.saddi.com/flup
This implementation also depends on Python Paste, which can be downloaded
from:
http://cheeseshop.python.org/pypi/Paste
Once you have done this, you can configure your fastcgi server to use
tilecache.fcgi.
Configuring FastCGI is beyond the scope of this documentation.
To set up a TileCache under IIS
===============================
Installing TileCache for use with IIS requires some additional configuration.
* Install Python for Windows
* Follow "Using Python Scripts with IIS" to setup Python CGI for IIS.
http://support.microsoft.com/kb/276494
* Edit metabase.xml to get correct Security Permissions for IIS 6.0.
http://blogs.msdn.com/david.wang/archive/2005/04/20/IIS6-CGI-Web-Service-Extension.aspx
* Edit tilecache.cgi to specify your configuration file explicitly:
svc = Service.load("C:\\TileCache\\tilecache.cfg")
Configuration
-------------
TileCache is configured by a config file, defaulting to tilecache.cfg.
There are several parameters to control TileCache layers that are applicable
to all layers:
bbox -- The bounding box of the Layer. The resolutions array defaults
to having resolutions which are equal to the bbox divided by
512 (two standard tiles).
debug -- Whether to send debug output to the error.log. Defaults to "yes",
can be set to "no"
description -- Layer description, used in some metadata responses. Default
is blank.
extension -- File extension of the layer. Used to request images from
WMS servers, as well as when writing cache files.
layers -- A string used to describe the layers. Typically passed directly
to the renderer. The WMSLayer sends this in the HTTP request,
and the MapServerLayer chooses which layer to render based on
this string. If no layer is provided, the layer name is used
to fill this property.
levels -- An integer, describing the number of 'zoom levels' or
scales to support. Overridden by resolutions, if passed.
mapfile -- The absolute file location of a mapfile. Required for
MapServer and Mapnik layers.
maxResolution -- The maximum resolution. If this is set, a resolutions
array is automatically calculated up to a number of
levels controlled by the 'levels' option.
metaTile -- set to "yes" to turn on metaTiling. This will request larger
tiles, and split them up using the Python Imaging library.
Defaults to "no".
metaBuffer -- an integer number of pixels to request around the outside
of the rendered tile. This is good to combat edge effects
in various map renderers. Defaults to 10.
metaSize -- A comma seperated pair of integers, which is used to
determine how many tiles should be rendered when using
metaTiling. Default is 5,5.
resolutions -- Comma seperate list of resolutions you want the TileCache
instance to support.
size -- Comma seperated set of integers, describing the width/height
of the tiles. Defaults to 256,256
srs -- String describing the SRS value. Default is "EPSG:4326"
type -- The type of layer. Options are:
* WMSLayer
* MapnikLayer
* MapServerLayer
url -- URL to use when requesting images from a remote WMS server. Required
for WMSLayer.
OpenLayers with TileCache
=========================
To run OpenLayers with TileCache the URL passed to the OpenLayers.Layer.WMS
constructor must point to the TileCache script, i.e. tilecache.cgi or
tilecache.py. As an example see the index.html file included in the TileCache
distribution.
Note: index.html assumes TileCache is set up under CGI (see above). If you set
up TileCache under mod_python you'd need to slighly modify index.html: the URL
passed to the OpenLayers.Layer.WMS constructor must point to the mod_python
script as opposed to the CGI script, so replace tilecache.cgi with
tilecache.py. Similarly, you would need to edit this URL if you were to use
TileCache with the standalone HTTP Server or FastCGI.
The most important thing to do is to ensure that the OpenLayers Layer
has the same resolutions and bounding box as your TileCache layer. You can define
the resolutions in OpenLayers via the 'resolutions' option or the 'maxResolution'
option on the layer. The maxExtent should be defined to match the bbox parameter
of the TileCache layer.
If you are using TileCache for overlays, you should set the 'reproject' option
on the layer to 'false'.
To use TileCache to seed your cache
===================================
* Set up the tilecache.cfg if you have not already done so in one of the
above configurations
* In /var/www/tilecache/TileCache, where /var/www/tilecache is the
directory resulting from the code extraction.
* The syntax is in the form of;
python ./Client.py
where:
url -- http://example.com/yourdir/tilecache.cgi? or
http://example.com/yourdir/tilecache.py
layer -- same layer name that is in the tilecache.cfg
zoom start -- Zoom level to start the process
zoom end -- Zoom level to end the process
bbox -- The bounding box (see the *** note *** above)
An example with zoom levels 5 through 12 would be like;
/usr/bin/python ./Client.py "http://example.com/yourdir/tilecache.cgi?"
Zip_Codes 5 12 "-118.12500,31.952162238,-116.015625,34.3071438563"
The bbox can be dropped and defaults to world lonlat(-180,-90,180,90)
/usr/bin/python ./Client.py "http://example.com/yourdir/tilecache.cgi?"
Zip_Codes 0 9
Keeping Your Disk Cache to a Reasonable Size
============================================
The tilecache_clean.py utility will remove the least recently accessed
tiles from a cache, down to a specified size.
usage: tilecache_clean.py [options]
options:
--version show program's version number and exit
-h, --help show this help message and exit
-s SIZE, --size=SIZE Maximum cache size, in megabytes.
-e ENTRIES, --entries=ENTRIES
Maximum cache entries. This limits the
amount of memory that will be used to store
information about tiles to remove.
The --entries option to tilecache_clean.py is optional, and is used to regulate
how much memory it uses to do its bookkeeping. The default value of 1 million
will hopefully keep RAM utilization under about 100M on a 32-bit x86 Linux
machine. If tilecache_clean.py doesn't appear to be keeping your disk cache
down to an appropriate size, try upping this value.
tilecache_clean.py is designed to be run from a cronjob like so:
00 05 * * * /usr/local/bin/tilecache_clean.py -s 500 /var/www/tilecache
Note that, on non-POSIX operating systems (particularly Windows),
tilecache_clean.py measures file sizes, and not disk usage. Because most
filesystems use entire file blocks for files smaller than a block, running 'du
-s' or similar on your disk cache after a cleaning may still return a total
cache size larger than you expect.
=30=