map::slippy(n)                 Mapping utilities                map::slippy(n)



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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  ?0.4?

       ::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

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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.

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



map                                   0.4                       map::slippy(n)
