[OSM-dev] Sphere / Web-Mercator
blake at hailmail.net
Thu Oct 9 17:00:09 BST 2008
If you are into reading, here's some code that nicely commented:
On Oct 9, 2008, at 8:38 AM, Dominik Spies wrote:
> 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?
> dev mailing list
> dev at openstreetmap.org
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