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[mkgmap-dev] A few thoughts on non-rectangular tiles

From Gerd Petermann gpetermann_muenchen at hotmail.com on Mon Dec 1 14:27:19 GMT 2014

Hi Steve,

> Tiles that would contain a land border need to be further split
> along that border. This could be done
> 1. Directly by splitter
> 2. By running mkgmap once for each country.
> 3. Some intermediate process.
> I believe it would be best in the long term for splitter to make the
> split, but perhaps the other strategies could be used temporarily in
> order to concentrate on other parts of the process.

Up to now I see no need to change splitter.
We already have the UnusedElementsRemoverHook,
I would try to add a similar method to
filter data which is outside of a given polygon.
Depending on the complexity of the polygon
this can be quite time consuming for just on tile.
If we try to do that in splitter and try to split e.g.
Europe, we have to store a lot of complex polygons
as we try to process many tiles at once.
I see only one possible advantage when doing it
in splitter: 
A perfect algo would be able to make sure that
all tiles for one country have a similar number of
nodes. When we use mkgmap for filtering a
single rectangular tile might just overlap a country
in a very small area, thus the resulting *.img would
be very small.


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