Provided by: tcllib_1.17-dfsg-1_all 
NAME
map::slippy - Common code for slippy based map packages
SYNOPSIS
package require Tcl 8.4
package require Tk 8.4
package require map::slippy ?0.5?
::map::slippy length level
::map::slippy tiles level
::map::slippy tile size
::map::slippy tile valid tile levels ?msgvar?
::map::slippy geo 2tile geo
::map::slippy geo 2tile.float geo
::map::slippy geo 2point geo
::map::slippy tile 2geo tile
::map::slippy tile 2point tile
::map::slippy point 2geo point
::map::slippy point 2tile point
::map::slippy fit geobox canvdim geobox zmin zmax
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DESCRIPTION
This package provides a number of methods doing things needed by all types of slippy-based
map packages.
API
::map::slippy length level
This method returns the width/height of a slippy-based map at the specified zoom
level, in pixels. This is, in essence, the result of
expr { [tiles $level] * [tile size] }
::map::slippy tiles level
This method returns the width/height of a slippy-based map at the specified zoom
level, in tiles.
::map::slippy tile size
This method returns the width/height of a tile in a slippy-based map, in pixels.
::map::slippy tile valid tile levels ?msgvar?
This method checks whether tile described a valid tile in a slippy-based map
containing that many zoom levels. The result is a boolean value, true if the tile
is valid, and false otherwise. For the latter a message is left in the variable
named by msgvar, should it be specified.
A tile identifier as stored in tile is a list containing zoom level, tile row, and
tile column, in this order. The command essentially checks this, i.e. the syntax,
that the zoom level is between 0 and "levels-1", and that the row/col information
is within the boundaries for the zoom level, i.e. 0 ... "[tiles $zoom]-1".
::map::slippy geo 2tile geo
Converts a geographical location at a zoom level (geo, a list containing zoom
level, latitude, and longitude, in this order) to a tile identifier (list
containing zoom level, row, and column) at that level. The tile identifier uses
pure integer numbers for the tile coordinates, for all geographic coordinates
mapping to that tile.
::map::slippy geo 2tile.float geo
Converts a geographical location at a zoom level (geo, a list containing zoom
level, latitude, and longitude, in this order) to a tile identifier (list
containing zoom level, row, and column) at that level. The tile identifier uses
floating point numbers for the tile coordinates, representing not only the tile the
geographic coordinates map to, but also the fractional location inside of that
tile.
::map::slippy geo 2point geo
Converts a geographical location at a zoom level (geo, a list containing zoom
level, latitude, and longitude, in this order) to a pixel position (list containing
zoom level, y, and x) at that level.
::map::slippy tile 2geo tile
Converts a tile identifier at a zoom level (tile, list containing zoom level, row,
and column) to a geographical location (list containing zoom level, latitude, and
longitude, in this order) at that level.
::map::slippy tile 2point tile
Converts a tile identifier at a zoom level (tile, a list containing zoom level,
row, and column, in this order) to a pixel position (list containing zoom level, y,
and x) at that level.
::map::slippy point 2geo point
Converts a pixel position at a zoom level (point, list containing zoom level, y,
and x) to a geographical location (list containing zoom level, latitude, and
longitude, in this order) at that level.
::map::slippy point 2tile point
Converts a pixel position at a zoom level (point, a list containing zoom level, y,
and x, in this order) to a tile identifier (list containing zoom level, row, and
column) at that level.
::map::slippy fit geobox canvdim geobox zmin zmax
Calculates the zoom level (whithin the bounds zmin and zmax) such that geobox (a
4-element list containing the latitudes and longitudes lat0, lat1, lon0 and lon1 of
a geo box, in this order) fits into a viewport given by canvdim, a 2-element list
containing the width and height of the viewport, in this order.
COORDINATE SYSTEMS
The commands of this package operate on three distinct coordinate systems, which are
explained below.
GEOGRAPHIC
Geographical coordinates are represented by Latitude and Longitude, each of which is
measured in degrees, as they are essentially angles.
Zero longitude is the Greenwich meridian, with positive values going east, and negative
values going west, for a total range of +/- 180 degrees. Note that +180 and -180 longitude
are the same meridian, opposite to greenwich.
zero latitude the Equator, with positive values going north and negative values going
south. While the true range is +/- 90 degrees the projection used by the package requires
us to cap the range at +/- 85.05112877983284 degrees. This means that north and south pole
are not representable and not part of any map.
TILES
While Geographical coordinates of the previous section are independent of zoom level the
tile coordinates are not.
Generally the integer part of tile coordinates represent the row and column number of the
tile in question, wheras the fractional parts signal how far inside the tile the location
in question is, with pure integer coordinates (no fractional part) representing the upper
left corner of the tile.
The zero point of the map is at the upper left corner, regardless of zoom level, with
larger coordinates going right (east) and down (south), and smaller coordinates going left
(west) and up (north). Again regardless of zxoom level.
Negative tile coordinates are not allowed.
At zoom level 0 the whole map is represented by a single, putting the geographic zero at
1/2, 1/2 of tile coordinates, and the range of tile coordinates as [0...1].
To go from a zoom level N to the next deeper level N+1 each tile of level N is split into
its four quadrants, which then are the tiles of level N+1.
This means that at zoom level N the map is sliced (horizontally and vertically) into 2^N
stripes, for a total of 4^N tiles, with tile coordinates ranging from 0 to 2^N+1.
PIXELS/POINTS
pixel coordinates, also called point coordinates are in essence tile coordinates scaled by
the size of the image representing a tile. This tile size currently has a fixed value,
256.
REFERENCES
[1] http://wiki.openstreetmap.org/wiki/Main_Page
KEYWORDS
geodesy, geography, latitute, location, longitude, map, slippy, zoom