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[mkgmap-dev] Sea generation

From Marko Mäkelä marko.makela at iki.fi on Thu Nov 4 19:24:46 GMT 2010

On Thu, Nov 04, 2010 at 08:06:18PM +0100, Lambertus wrote:
>So I'm looking forward to any improvements that work without 
>hand-picking tile borders.

You are cutting a planet extract yourself, aren't you? My problems are 
different, because I am relying on an area extract that is not 
rectangular and lacks information of the bounding polygon. You could be 
suffering from bad data. You know, I have been told that the sea areas 
on the Mapnik rendition are based on some fixed data and the 
natural=coastline lines are ignored. It is relatively easy to keep a 
small area free from mkgmap-reported issues. Usually there are fewer 
than 5 errors when I do a test build, and after fixing the issues, the 
next day I typically get an error-free map. For any bigger area, I guess 
you can never get a mkgmap-complaint-free map, not even if you had the 
resources to fix all the reported errors by the time the next day's 
extract is cloned off.

I have been toying with the idea of hand-picking tile borders for 
Estonia as well, but I don't know if it is worth my trouble. I'd guess 
that the country extract (as opposed to an Europe or planet extract) is 
most useful for islands. Finland is an island in some sense: you can't 
cross the Russian border without a passport and visa, the land borders 
to Sweden and Norway in the north are very far away from most of the 
population, and you will have plenty of time to switch maps when 
crossing the sea borders. Sweden, Norway and Estonia are less of 
islands, because they have easily crossable land borders. The map would 
have to lump several countries together in order to be practical, and I 
don't want to start downloading and cutting the Europe extract.

When it comes to incomplete multipolygons that are severed by the tile 
borders, I guess that mkgmap should just ignore incomplete polygons that 
are totally outside the bounding box. Maybe this has been implemented 
already, because I am seeing very few multipolygon warnings nowadays. I 
should check if there is anything wrong about the two multipolygons that 
mkgmap now complains about near the tile borders.


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