1map::slippy(n)                 Mapping utilities                map::slippy(n)
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5______________________________________________________________________________
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NAME

8       map::slippy - Common code for slippy based map packages
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SYNOPSIS

11       package require Tcl  8.4
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13       package require Tk  8.4
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15       package require map::slippy  ?0.5?
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17       ::map::slippy length level
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19       ::map::slippy tiles level
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21       ::map::slippy tile size
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23       ::map::slippy tile valid tile levels ?msgvar?
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25       ::map::slippy geo 2tile geo
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27       ::map::slippy geo 2tile.float geo
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29       ::map::slippy geo 2point geo
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31       ::map::slippy tile 2geo tile
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33       ::map::slippy tile 2point tile
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35       ::map::slippy point 2geo point
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37       ::map::slippy point 2tile point
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39       ::map::slippy fit geobox canvdim geobox zmin zmax
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41______________________________________________________________________________
42

DESCRIPTION

44       This  package  provides  a number of methods doing things needed by all
45       types of slippy-based map packages.
46

API

48       ::map::slippy length level
49              This method returns the width/height of a  slippy-based  map  at
50              the  specified  zoom  level, in pixels. This is, in essence, the
51              result of
52
53
54                expr { [tiles $level] * [tile size] }
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56
57       ::map::slippy tiles level
58              This method returns the width/height of a  slippy-based  map  at
59              the specified zoom level, in tiles.
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61       ::map::slippy tile size
62              This method returns the width/height of a tile in a slippy-based
63              map, in pixels.
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65       ::map::slippy tile valid tile levels ?msgvar?
66              This method checks whether tile described  a  valid  tile  in  a
67              slippy-based map containing that many zoom levels. The result is
68              a boolean value, true if the tile is valid, and false otherwise.
69              For  the  latter a message is left in the variable named by msg‐
70              var, should it be specified.
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72              A tile identifier as stored in tile is a  list  containing  zoom
73              level, tile row, and tile column, in this order. The command es‐
74              sentially checks this, i.e. the syntax, that the zoom  level  is
75              between  0  and  "levels-1", and that the row/col information is
76              within the boundaries for the zoom level, i.e.  0  ...   "[tiles
77              $zoom]-1".
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79       ::map::slippy geo 2tile geo
80              Converts  a  geographical  location at a zoom level (geo, a list
81              containing zoom level, latitude, and longitude, in  this  order)
82              to  a tile identifier (list containing zoom level, row, and col‐
83              umn) at that level. The tile identifier uses pure  integer  num‐
84              bers  for  the  tile coordinates, for all geographic coordinates
85              mapping to that tile.
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87       ::map::slippy geo 2tile.float geo
88              Converts a geographical location at a zoom level  (geo,  a  list
89              containing  zoom  level, latitude, and longitude, in this order)
90              to a tile identifier (list containing zoom level, row, and  col‐
91              umn) at that level. The tile identifier uses floating point num‐
92              bers for the tile coordinates, representing not  only  the  tile
93              the geographic coordinates map to, but also the fractional loca‐
94              tion inside of that tile.
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96       ::map::slippy geo 2point geo
97              Converts a geographical location at a zoom level  (geo,  a  list
98              containing  zoom  level, latitude, and longitude, in this order)
99              to a pixel position (list containing zoom level, y,  and  x)  at
100              that level.
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102       ::map::slippy tile 2geo tile
103              Converts  a tile identifier at a zoom level (tile, list contain‐
104              ing zoom level, row, and  column)  to  a  geographical  location
105              (list  containing  zoom  level, latitude, and longitude, in this
106              order) at that level.
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108       ::map::slippy tile 2point tile
109              Converts a tile identifier at a zoom level (tile,  a  list  con‐
110              taining  zoom  level, row, and column, in this order) to a pixel
111              position (list containing zoom level, y, and x) at that level.
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113       ::map::slippy point 2geo point
114              Converts a pixel position at a zoom level (point, list  contain‐
115              ing  zoom level, y, and x) to a geographical location (list con‐
116              taining zoom level, latitude, and longitude, in this  order)  at
117              that level.
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119       ::map::slippy point 2tile point
120              Converts  a  pixel  position at a zoom level (point, a list con‐
121              taining zoom level, y, and x, in this order) to a  tile  identi‐
122              fier  (list  containing  zoom  level,  row,  and column) at that
123              level.
124
125       ::map::slippy fit geobox canvdim geobox zmin zmax
126              Calculates the zoom level (whithin the  bounds  zmin  and  zmax)
127              such  that geobox (a 4-element list containing the latitudes and
128              longitudes lat0, lat1, lon0 and lon1 of a geo box, in  this  or‐
129              der)  fits  into  a  viewport given by canvdim, a 2-element list
130              containing the width and height of the viewport, in this order.
131

COORDINATE SYSTEMS

133       The commands of this package operate on three distinct coordinate  sys‐
134       tems, which are explained below.
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136   GEOGRAPHIC
137       Geographical  coordinates  are  represented  by Latitude and Longitude,
138       each of which is measured in degrees, as they are essentially angles.
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140       Zero longitude is the Greenwich meridian, with  positive  values  going
141       east,  and negative values going west, for a total range of +/- 180 de‐
142       grees. Note that +180 and -180 longitude are the same  meridian,  oppo‐
143       site to greenwich.
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145       zero  latitude  the Equator, with positive values going north and nega‐
146       tive values going south. While the true range is  +/-  90  degrees  the
147       projection  used  by  the  package  requires us to cap the range at +/-
148       85.05112877983284 degrees. This means that north and south pole are not
149       representable and not part of any map.
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151   TILES
152       While  Geographical coordinates of the previous section are independent
153       of zoom level the tile coordinates are not.
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155       Generally the integer part of tile coordinates represent  the  row  and
156       column number of the tile in question, wheras the fractional parts sig‐
157       nal how far inside the tile the location in question is, with pure  in‐
158       teger coordinates (no fractional part) representing the upper left cor‐
159       ner of the tile.
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161       The zero point of the map is at the upper left  corner,  regardless  of
162       zoom  level,  with  larger  coordinates  going  right  (east)  and down
163       (south), and smaller coordinates going  left  (west)  and  up  (north).
164       Again regardless of zxoom level.
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166       Negative tile coordinates are not allowed.
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168       At  zoom  level 0 the whole map is represented by a single, putting the
169       geographic zero at 1/2, 1/2 of tile coordinates, and the range of  tile
170       coordinates as [0...1].
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172       To  go  from  a  zoom level N to the next deeper level N+1 each tile of
173       level N is split into its four quadrants, which then are the  tiles  of
174       level N+1.
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176       This  means  that  at  zoom level N the map is sliced (horizontally and
177       vertically) into 2^N stripes, for a total of 4^N tiles, with tile coor‐
178       dinates ranging from 0 to 2^N+1.
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180   PIXELS/POINTS
181       pixel  coordinates,  also  called point coordinates are in essence tile
182       coordinates scaled by the size of the image representing a  tile.  This
183       tile size currently has a fixed value, 256.
184

REFERENCES

186       [1]    http://wiki.openstreetmap.org/wiki/Main_Page
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KEYWORDS

189       geodesy, geography, latitute, location, longitude, map, slippy, zoom
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193tcllib                                0.5                       map::slippy(n)
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