.. _mapcache_seed:

*****************************************************************************
Seeder
*****************************************************************************

:Author: Thomas Bonfort
:Contact: tbonfort at terriscope.fr
:Author: Mathieu Coudert
:Contact: mathieu.coudert at gmail.com

Mod-mapcache ships with an advanced seeding tool, whose main features are:
 * configurable number of seeding threads, to speed up the rendering
 * ability to reseed tiles older than a certain timestamp
 * ability to seed tiles given a shapefile/OGR datasource

Usage
-----------------------------------------------------------------------------

The seeding utility is named mapcache_seed, and is located under your install
directory (default is /usr/local/bin).


Commandline Options
================================================================================

Options are available in short and long versions (e.g. -c or --config).

**-c | --config [file]**: path to the mapcache.xml configuration file that
contains the tilesets that need to be seeded.

**-D | --dimension "DIMENSION=VALUE"**: used to specify which dimension to use
if the tileset supports dimensions. Can be used multiple times to set multiple
dimensions, e.g. -D "DIM1=VAL1" -D "DIM2=VAL2".

**-e | --extent minx,miny,maxx,maxy**: bounding box of the area to seed.

**-f | --force**: force recreation of existing tiles.

**-g | --grid [grid]**: name of the grid that must be seeded (the selected
tileset must reference the given grid).

**-h | --help**: show help.

**-i | --iteration-mode**: either "*drill-down*" or "*level-by-level*".
Default is to use drill-down for g, WGS84 and GoogleMapsCompatible grids, and
level-by-level for others. Use this flag to override.

**-m | --mode**: the mode to use the seeder: "*seed*", "*delete*" or
"*transfer*".
Default is seed (*mode: seed*).

**-M | --metasize**: override metatile size while seeding, e.g. 8,8.

**-n | --nthreads**: number of parallel threads that should be used to request
tiles from the WMS source. The default is 1, but can be set higher if the WMS
server can withstand parallel requests. (As a rule of thumb, the value chosen
here should never be much higher than the number of CPUs on the WMS server.)

.. note:: This option is imcompatible with the **-p | --nprocesses** option.


**-o | --older [timestamp|now]**: only seed tiles that are older than the given
value. The value can either be the string "*now*", or a date formatted like
year/month/day hour:minute, e.g. "2011/01/31 20:45".

.. note:: A full timestamp should be quoted.

**-p | --nprocesses**: number of parallel processes that should be used to
request tiles from the WMS source.

.. note::

   This option is imcompatible with the **-n | --nthreads** option.

.. warning::

   When working with multiple processes (-p switch) and SQLite cache
   backends, some errors may appear under high concurrency when writing to the
   SQLite database (error: SQL logic error or missing database (1)).
   Upgrading to SQLite >= 3.7.15 seems to resolve this issue.

**-q | --quiet**: don't print progress messages to the standard output.

**-t | --tileset [tileset]**: name of the tileset that must be seeded.

**-v | --verbose**: print verbose debugging info (if compiled in).

**-x | --transfer**: the tileset to transfer when seeder is run in transfer
mode.

**-z | --zoom minzoom,maxzoom**: start and end zoom levels that must be seeded.


Optional Commandline Options When Using OGR/GEOS
================================================================================

At compile time, if OGR and GEOS are found on the system, the seeder tool will
support additional options to seed only the tiles that cover an arbitrary
geographical area. *Important:* Note that, for the time being, the OGR
datasource should be in the same projection as the grid you are seeding, as
there is no automatic reprojection from the datasource projection to the grid
projection.

**-d | --ogr-datasource [ogr_datasource]**: OGR connection to the spatial source.
Consult the OGR documentation for all that is supported. In the simplest case
(e.g. a Shapefile), this is just the full filename of the shapefile.

**-l | --ogr-layer [ogr_layer]**: for datasources that contain multiple layers
(e.g. PostGIS, with multiple tables), determines which layer will be used.

**-s | --ogr-sql [ogr_sql]**: OGR SQL expression that can be applied (see `OGR SQL`_).

**-w | --ogr-where [ogr_where]**: SQL "where" expression to filter out returned values.
This would typically be used to select only the geometry of a given country if the
datasource contains all the world contours.

Important Note
================================================================================

The seeding utility must be run under the same user account as the
user running the webserver. This is required so the permissions on the tiles
created by the seeder are accessible by the webserver, and conversely so the
seeder has the rights to write files to directories created by the webserver.


A sample seeding session goes like this:

::

  [user@host]$ sudo www-data
  [www-data@host]$ /path/to/mapcache/src/mapcache_seed -c /path/to/www/conf/mapcache.xml [[options]]
  [www-data@host]$ logout
  [user@host]$


Examples
================================================================================

Seed the "osm" tileset with the "g" (Google / Web Mercator) grid:
::

   ./src/mapcache_seed -c mapcache.xml -t osm -g g

Seed levels 0 through 12:
::

   ./src/mapcache_seed -c mapcache.xml -t osm -g g -z 0,12

Given a shapefile that contains the world country contours, seed only the
areas that are covered by land (i.e. skip the oceans). Also, use 4 request
threads in parallel:
::

   ./src/mapcache_seed -c mapcache.xml -t osm -g g -z 0,12 -n 4 -d /path/to/seed.shp

Same as beforehand, but only seed the USA (notice the quote usage, required to
create valid SQL with a single-quoted 'US':
::

   ./src/mapcache_seed -c mapcache.xml -t osm -g g -z 0,12 -n 4 -d /path/to/seed.shp -w "FIPS_A2='US'"

Reseed levels 0 to 12 (this could also be done by deleting the cache for levels
0 to 12 and doing a classic seed, but doing so this way does not slow down
access from web clients):
::

   ./src/mapcache_seed -c mapcache.xml -t osm -g g -z 0,12 -o now


.. _`OGR SQL`: http://www.gdal.org/ogr/ogr_sql.html
