Hi Dominic, If you are into reading, here's some code that nicely commented:
http://trac.osgeo.org/gdal/browser/sandbox/klokan/globalmaptiles.py Cheers, Dane On Oct 9, 2008, at 8:38 AM, Dominik Spies wrote: > Hi, > > I'm trying to implement some projection-code for a project of mine.. > But I have some trouble with the Mercator projection. > > I understood that the projection we use in the slippy map is called > Sphere / Web-Mercator, or EPSG:900913 or EPSG:3785 and is also used by > Google, MS, Yahoo and so on.. > > So there is some description on MSDN > (http://msdn.microsoft.com/en-us/library/bb259689.aspx) which says: > > y = 0.5 – log((1 + sin(Latitude)) / (1 – sin(Latitude))) / (4 * pi) > > on some other pages and wikipedia I found that one: > > y = 0.5 * ln( (1 + sin(Latitude)) / (1 – sin(Latitude)) ) > > where this is called the projection for GoogleMaps. > > > So - this is not the same. I understand that the first one is somehow > clipped to Lat +-85.05... and then scaled to 0 to 1. > > Huh, the second one. what scale is this? I can't figure out how to > use it.. > > Can someone point me into the right direction? Something to read? > > Regards, > > Dominik > > _______________________________________________ > dev mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/dev _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
