[Tilesathome] Coastline and ocean leakage in Iceland

[Rob Reid]

Ævar Arnfjörð Bjarmason wrote the following on 02/10/2008 06:48:
> A bunch of tiles covering Iceland are inappropriately either blue or
> white squares on land or near the coast:
>
> http://openstreetmap.org/?lat=65.47&lon=-22.71&zoom=8&layers=0B00FTF
>
> This also happens inland:
>
> http://openstreetmap.org/?lat=65.396&lon=-14.227&zoom=9&layers=0B00FTF
>
> I can't see what the problem is, here's perhaps a better example where
> an area of the ocean is rendered as if it's a landmass but there's no
> island (or anything else but the ocean) in that area:
>
> http://openstreetmap.org/?lat=65.7839&lon=-23.8626&zoom=13&layers=0B00FTF
>
> What's the problem?
>   
Osmarender uses a file called oceantiles_12.dat to establish if a tile 
at zoom 12 is ocean or land because when it is rendering it only has the 
data for that tile and so may not know where the nearest coastline is.

Looking at your 3rd example the z12 tile in question is here :
http://server.tah.openstreetmap.org/Browse/details/tile/12/1776/1044/

Checking oceantiles for this tiles gives the following result showing it 
marked as a land tile :

     ./png2tileinfo.pl check 1776 1044
    oceantiles_12.png(1776, 1044) = 1 (*land*)

If you run tilesAtHome you should already have the png2tileinfo 
directory which contain the tools for fixing this.
If not you can check it out with svn from here :
http://svn.openstreetmap.org/applications/rendering/png2tileinfo/
And read the README for details on how to check/set tiles.

To commit changes you will need an svn account.

If that all seems a bit complicated let me know and I'll add Iceland to 
the places I've been doing oceantiles fixes for.

rcr