[Tilesathome] Strange rendering of straight lines

[Dirk-Lüder Kreie]

Matthias Julius schrieb:
> Maarten Deen <mdeen at xs4all.nl> writes:
> 
>> I'm a bit puzzled for the reason why this gets rendered as it does:
>> <http://informationfreeway.org/?lat=-84.951&lon=-144.66&zoom=12&layers=B0000F000F>
> 
> It looks really interesting.
> 
>> Tiles are
>> <http://server.tah.openstreetmap.org/Browse/details/tile/12/402/4083/>
>> <http://server.tah.openstreetmap.org/Browse/details/tile/12/402/4082/>
>> <http://server.tah.openstreetmap.org/Browse/details/tile/12/401/4082/>
>>
>> In JOSM, this is a straight line. Why does the render mess this up so much?
>> Two tiles have a turn in the coastline, and the middle tile is not in line with 
>> the outer two.
>>
>> If you look in JOSM with the slippymap plugin, the rendering is way off of where 
>> it should be.
>>
>> And the coast is riddled with these tiles.
>> Is this some side-effect from being close to the pole?
> 
> I guess it is a projection error.  Those are always more visible at
> higher latitudes.
> 
> Where do the coastlines get closer to where they should be?  At the
> top, middle or bottom of the tiles?

It starts to become more than a pixel at about 84.1° South

If the node is in the bottom half of the tile, the rendering is too far 
north, if the node is around the center, everything looks fine, and if 
the node is in the upper half of the tile, the rendering is too far to 
the south.

-- 

Dirk-Lüder "Deelkar" Kreie
Bremen - 53.0952°N 8.8652°E

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