Provided by: tcllib_1.19-dfsg-2_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