On Thu, Feb 12, 2009 at 09:19:24AM +0000, Nick Whitelegg wrote: > Have now got the right projection string working, thanks. However one > thing I'd like to clarify in my mind (and apologies if this is > slightly OT) is what the "Google Mercator projection units", as > obtained by the code below, actually represent. They do *not* appear > to correspond to pixels at any given zoom level: I've tested this on > three nearby points on the Earth and the differences in "Google > projection units" between them do not appear to correspond exactly to > pixels at any given zoom level. So is there a simple arithmetic > relation between "Google projection units" and pixels at any given > zoom level?
The units of this mercator projection are meters. At the most zoomed out level, a single pixel is: 20037508.34 / 128 = 156543.03390625 meters in each direction. Each time you zoom in, that number cuts in half. Regards, -- Christopher Schmidt MetaCarta _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
