[OSM-dev] Y-Boundary of Mercator-Projection

Matthias Brandt mb at blau.de
Wed Feb 4 12:46:58 GMT 2009

Tom Hughes wrote:
> Matthias Brandt wrote:
>> Tom Hughes wrote:
>>> Matthias Brandt wrote:
>>>> i've searched the archive of this mailinglist and the wiki about 
>>>> the magical y-boundary set to 85.05113° (respective 180° projected) 
>>>> in the Mercator Projection.
>>> Did you have an alternative value in mind?
>> Not really. But I would like to know, if there is any reason for 
>> this. I'm writing my Bachelorthesis about OpenStreetMaps and I would 
>> like to explain this bound.
> If what you're asking is why it doesn't just go to 90 degrees then you 
> might want to consider what happens to the projection function in the 
> limit as the latitude approaches 90 degrees...
Yes, I know the problem with values reaching 90°.

Iván Sánchez Ortega wrote:
> Quadtiles, quadtiles, quadtiles. Having a big square allows you to
> subdivide images in a fashion similar to quadtrees. Using rectangles would
> mess things up.
Thank you! That's what I needed to know :-)


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