Every tile has a sice of BO_TILE_SIZE * BO_TILE_SIZE. BO_TILE_SIZE is defined in
defines.h and is currently 48. This will probably not change and therefore every
tile has a size of 48*48.

The ground pixmap (currently only earth.png) consists of 32 (8*4) tiles horizonatlly
and 39 (I hope...) tiles vertically. This means the pixmap consists of 32*39
tiles each with a size of 48*48.

I have not yet found out the correct order of the pixmaps so here is what I have
so far.
Everything I'm telling now refers to the horizontally couning, so e.g. the tile
33 means the first tile in the second line.

The tiles are grouped into transitions and types. Each transition is part of a
group. One transition consists of 4 tiles which all belong to this transition
and this type (aka groundType).

The pixmap file starts with "without" a transition. IMHO this is a small bug as
it should be transition_Unknown - but that doesn't matter.
Without transition means that the tile just shows the plain pix. The order
- "Unknown"
- "Deep Water"
- "Water"
- "Grass"
- "Desert"
- "GrassMineral"
- "GrassOil"
as said above all these have four different tiles, so this makes 7*4=28 tiles.

Now the real transition start. First the type is Grass->Water. Dunno how to
describe this in boson... it might be that this has (in boson) the type water
but it might be possible that this has the type grass... I will look at this
someday.
All following tiles are of this type Grass->Water. The Transition Order:
- Up Left
- Up Right
- Down Left
- Down Right
- Up
- Down
- Left
- Right
(=> makes 8*4=32 tiles. )
Where e.g. "Right" means that the Water is on the right side (the grass ends at
the right).
Now come the inverted tranitions (FIXME: dunno what inverted means...):
- Up Left inverted
- Up Right inverted
- Down Left inverted
- Down Right inverted
(=> makes 4*4=16 tiles)
==> makes 32+16=48 tiles.

About the next i'm not fully sure (once again): It seems that this is the type
"Water->Grass" as there seems to be more water than grass on the tiles.
==> makes again 48 tiles.
