bionic (3) map_slippy_cache.3tcl.gz

NAME

       map::slippy::cache - Management of a tile cache in the local filesystem

SYNOPSIS

       package require Tcl  8.4

       package require Tk  8.4

       package require img::png

       package require map::slippy

       package require map::slippy::cache  ?0.2?

       ::map::slippy::cache cacheName cachedir provider

       cacheName valid tile ?msgvar?

       cacheName exists tile

       cacheName get tile donecmd

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DESCRIPTION

       This  package  provides  a  class  for  managing  a  cache  of  tiles  for slippy-based maps in the local
       filesystem.

API

       ::map::slippy::cache cacheName cachedir provider
              Creates the cache cacheName and configures it with both the path to the  directory  contaiing  the
              locally  cached  tiles  (cachedir), and the command prefix from which it will pull tiles asked for
              and not yet known to the cache itself (provider).

              The result of the command is cacheName.

   METHODS
       cacheName valid tile ?msgvar?
              This method checks the validity of a the given tile identifier.  This is a convenience wrapper  to
              ::map::slippy tile valid and has the same interface.

       cacheName exists tile
              This  methods  tests whether the cache contains the specified tile or not. The result is a boolean
              value, true if the tile is known, and false otherwise. The tile is identified by a list containing
              three elements, zoom level, row, and column number, in this order.

       cacheName get tile donecmd
              This  is the main method of the cache, retrieving the image for the specified tile from the cache.
              The tile identifier is a list containing three elements, the zoom level, row, and column number of
              the tile, in this order.

              The  command  refix  donecmd will be invoked when the cache either knows the image for the tile or
              that no image will forthcoming.  It will be invoked with either 2 or 3 arguments, i.e.

              [1]    The string set, the tile, and the image.

              [2]    The string unset, and the tile.

              These two possibilities are used to either signal the image for the tile, or that the tile has  no
              image defined for it.

              When  the  cache  has  no  information  about  the tile it will invoke the provider command prefix
              specified during its construction, adding three  arguments:  The  string  get,  the  tile,  and  a
              callback  into  the cache. The latter will be invoked by the provider to either transfer the image
              to the cache, or signal that the tile has no image.

              When multiple requests for the same tile are made only one request will be issued to the provider.

REFERENCES

       [1]    http://wiki.openstreetmap.org/wiki/Main_Page

KEYWORDS

       cache, filesystem, location, map, slippy, tile, zoom