Hi Oliver

> For the overlapping maps have a look:
> 
> http://www.qlandkarte.org/shot8.png

This about how the planet XML file is split into the individual xml files
for each tile.  The splitter program ideally would clip every feature at the
boundary but this is difficult as there is no polygon primitive in OSM so
you need to do half the work just to know how to clip it.

Because of that I implemented a clipping feature within mkgmap so that a
map splitting program can just just include every feature that is within a
tile, and not worry about overspilling.  It just has to include a <bounds/>
element which is a standard element in OSM.

I downloaded three tiles from the computerteddy set and this is how they
look:

http://www.mkgmap.org.uk/tmp/before.png

The overspill pushes the tile boundary out and causes overlap.

I manually added <bounds minlat=".." maxlat=".." minlon=".." maxlon=".."/>
elements to the source OSM files and ran mkgmap on it again.
This time the tiles are exactly the right size and there is no overlap.

http://www.mkgmap.org.uk/tmp/after.png

This doesn't work fully with the existing tiles, because each feature is
placed into just the one file, rather than being repeated in each tile that
the feature overlaps.

I don't think the code for the actual program that splits the planet file
is available so I don't know how it works or how easy it would be to
modify it to do that.  But if it could then you would get perfect
non-overlapping .img tiles.

..Steve

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