README for png2tileinfo
-----------------------

This is the "source" for the oceantiles_12.dat file used in
close-areas.pl and in lowzoom.pl of the tilesAtHome project, as
well as the tahngo t@h server.

The oceantiles_12.dat file contains two bits for every level-12
tile in the world, specifying whether it is a land tile, a sea tile,
a coastal tile, or unknown.

The file is easy to access by the programs using it, but difficult
to edit. So here is the "source data" in the form of a large PNG
file 4096x4096 pixels for the whole planet, in which each pixel
corresponds to one level-12 tile and may have one of four colours:

white - coastline intersects with this tile
green - no coastline intersect, land tile
blue -  no coastline intersect, sea tile
black - unknown

If you find errors in the data file - i.e. an inland area rendered
blue or a sea area not rendered blue -, you can simply fix the PNG file
with any image editor, then run png2tileinfo, and you have a new
data file. (Please make sure to upload both the .png file that you
changed and the .dat file created!)

Please note that the code is picky about the colours used. Nothing
but "pure" colors will do - blue has to be 0,0,255, green has to be
0,255,0, black is 0,0,0 and white 255,255,255.

Main usage:
-----------
% cd applications/rendering/png2tileinfo
% svn update
% perl png2tileinfo.pl check 3762 2471
oceantiles_12.png(3762, 2471) = 3 (mixed)
% perl png2tileinfo.pl set 3762 2471 land
% perl png2tileinfo.pl

[wait until file generated...]

% svn commit

Programm help text shown for wrong arguments:
---------------------------------------------
1 Usage: png2tileinfo.pl check <x> <y>
2        png2tileinfo.pl set <x> <y> <land|sea|mixed> ...
3        png2tileinfo.pl diff oldfile.png newfile.png
4        png2tileinfo.pl svndiff
5        png2tileinfo.pl view
6        png2tileinfo.pl copydiff [oldfile.png newfile.png targetfile.png]

1) check the type of a tile

2) set the type of a tile

3) show the differences between two files

4) show the difference between current state and the SVN copy of last checkout

5) view all tiles as ASCII text

6) copy differences between old and new file into target file
   if no file names are given the software searches for two
   oceantiles_12.png.r<num> files which are the result of a checkout conflict
   and copies the differences between these two files in the oceantiles_12.png
   This is required when the file has been changed in SVN during own changes.


Note
---------------------------------------------
Please note that changes which are done through informationfreeway.org do NOT
automatically end up here. The changes are stored localy on that host and are
manually and erratically incorporated here. A better way for changes is thus
to mail the change request to the list T@h mailing list at
<tilesathome@openstreetmap.org>.