NAME
tilecache - Cache and serve map tiles
DESCRIPTION
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.
TileCache was developed by MetaCarta Labs and released to the public
under a BSD license.
The TileCache was designed as a companion to OpenLayers, the BSD
licensed web mapping interface. If you are using TileCache with
OpenLayers, please read the section of this readme which describes how
to do so. For additional 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 tilecache@openlayers.org.
RUNNING UNDER CGI
· TileCache should have a cgi installed under /usr/lib/cgi-bin, called
tilecache.cgi. This is accessible from
http://yourmachine.example.com/cgi-bin/tilecache.cgi.
· Edit /etc/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.
· Visit:
http://yourmachine.example.com/cgi-bin/tilecache.cgi?LAYERS=basic&SERVICE=WMS&BBOX=-180,-90,0,90
· Or visit:
http://yourmachine.example.com/cgi-bin/tilecache.cgi/1.0.0/basic/0/0/0.png
· If you see a tile, TileCache is working correctly.
RUNNING UNDER MOD_PYTHON
· Edit /etc/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:
Alias /tiles /var/lib/python-support/python2.4/tilecache/
<Directory /var/lib/python-support/python2.4/>
SetHandler python-program
PythonHandler TileCache.Service
PythonOption TileCacheConfig /etc/tilecache.cfg
</Directory>
· 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!
RUNNING STANDALONE (UNDER WSGI)
TileCache includes standalone HTTP server which uses the WSGI handler.
This implementation depends on Python Paste , which can be installed
via the python-paste package.
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:
/usr/sbin/tilecache_http_server
This will start a webserver listening on port 8080 (by default), after
which you should be able to open:
http://yourmachine.example.com:8080/1.0.0/basic/0/0/0.png
to see your first tile.
RUNNING UNDER FASTCGI
TileCache includes 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 via the python-paste package:
Once you have done this, you can configure your fastcgi server to use
tilecache.fcgi.
Configuring FastCGI is beyond the scope of this documentation.
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 separated pair of integers, which is used to determine
how many tiles should be rendered when using metaTiling. Default
is 5,5.
resolutions
Comma separate list of resolutions you want the TileCache
instance to support.
size Comma separated 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, ImageLayer
url URL to use when requesting images from a remote WMS server.
Required for WMSLayer.
watermarkImage
The watermarkImage parameter is assigned on a per-layer basis.
This is a fully qualified path to an image you would like to
apply to each tile. We recommend you use a watermark image the
same size as your tiles. If using the default tile size, you
should use a 256x256 image. NOTE: Python Imaging Library DOES
NOT support interlaced images.
watermarkOpacity
The watermarkOpacity parameter is assigned on a per-layer basis.
This configures the opacity of the watermark over the tile, it
is a floating point number between 0 and 1. Usage is optional
and will otherwise default.
extent_type
Setting this to ´loose´ will allow TileCache to generate tiles
outside the maximum bounding box. Useful for clients that don´t
know when to stop asking for tiles.
tms_type
Setting this to "google" will cause tiles to switch vertical
order (that is, following the Google style x/y pattern).
USING TILECACHE WITH OPENLAYERS
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 example-
cgi.html file included in the TileCache distribution, under
/usr/share/doc/tilecache/examples/.
Note: example-cgi.html assumes TileCache is set up under CGI (see
above). If you set up TileCache under mod_python you´d need to slighly
modify example-cgi.html: the URL passed to the OpenLayers.Layer.WMS
constructor must point to the mod_python script as opposed to the CGI
script. 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.
USING TILECACHE WITH MAPSERVER
MapServer has a map level metadata option, labelcache_map_edge_buffer,
which is set automatically by TileCache to the metaBuffer plus five
when metaTiling is on, if it is not set in the mapfile.
If you are using MetaTiling, be aware that MapServer generates
interlaced PNG files, which PIL will not read. See
http://mapserver.gis.umn.edu/docs/faq/pil_mapscript on how to resolve
this.
SEEDING YOUR TILECACHE
The tilecache_seed utility will seed tiles in a cache automatically.
You will need to have TileCache set up in one of the previously
described configurations.
Usage
/usr/sbin/tilecache_seed <url> <layer> [<zoom start> <zoom stop>
[<bbox>]]
Arguments
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 to seed
Seeding by center point and radius
If called without zoom level arguments, tilecache_seed.py will assume
that it needs to read a list of points and radii from standard input,
in the form:
<lat>,<lon>,<radius>
<lat>,<lon>,<radius>
<lat>,<lon>,<radius>
<lat>,<lon>,<radius>
<ctrl + d>
The format of this file is:
lon the position(s) to seed longitude
lat the position(s) to seed latitude
radius the radius around the lon/lat to seed in degrees
Examples
An example with zoom levels 5 through 12 would be like;
$ /usr/sbin/tilecache_seed "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/sbin/tilecache_seed.py "http://example.com/yourdir/tilecache.cgi?" Zip_Codes 0 9
In center point/radius mode, the zoom level range is not specifiable
from the command-line. An example usage might look like:
$ /usr/sbin/tilecache_seed.py "http://example.com/yourdir/tilecache.cgi?" Zip_Codes
-118.12500,31.952162238,0.05
-121.46327,32.345345645,0.08
<Ctrl+D>
... the seeding will then commence ...
CLEANING YOUR TILECACHE
The tilecache_clean utility will remove the least recently accessed
tiles from a cache, down to a specified size.
Usage
/usr/sbin/tilecache_clean [options] <cache_location>
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.
Notes
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 is designed to be run from a cronjob like so:
00 05 * * * /usr/sbin/tilecache_clean.py -s500 /var/www/tilecache
TROUBLESHOOTING
Occasionally, for some reason, when using meta tiles, your server may
leave behind lock files. If this happens, there will be files in your
cache directory with the extension ´.lck´. If you are seeing tiles not
render and taking multiple minutes before returning a 500 error, you
may be suffering under a stuck lock.
Removing all files with extension ´.lck´ from the cache directory will
resolve this problem.
SEE ALSO
memcached(8)
http://tilecache.org/
http://openlayers.org/
http://wiki.osgeo.org/index.php/WMS_Tiling_Client_Recommendation
http://wiki.osgeo.org/index.php/Tile_Map_Service_Specification
AUTHOR
crschmidt@metacarta.com
COPYRIGHT
(c) 2006-2007 MetaCarta, Inc. Distributed under the BSD license.
