[OSM-dev] Projection problems

Jon Burgess jburgess777 at googlemail.com
Tue Dec 16 20:49:47 GMT 2008


On Tue, 2008-12-16 at 17:27 +0000, Thomas Wood wrote:
> osm2pgsql uses a spherical mercator projection which cuts down on the
> amount of math required to produce a reasonable estimation of the
> earth for our uses.
> It's not a 'proper' projection in the GIS sense, but it works for our
> purposes.
> 
> http://wiki.openstreetmap.org/index.php/Mercator#Spherical_Mercator
> 
> I'm not sure what scaling factor osm2pgsql uses

For the spherical project we assume a radius of exactly 6378137m which
gives a circumference of 40075016.6856m. This maps +-180 degrees of
longitude to +-20037508.3428.

	Jon







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