I'm looking at the documentation for Google Map Overlays and the section on Google Maps Coordinates, located here:
http://code.google.com/apis/maps/documentation/overlays.html#Google_Maps_Coordinates The documentation says: "Each tile within Google Maps consists of 256 x 256 pixels. A point on a particular tile can therefore be referenced using a GPoint x,y pair. The origin (0,0) for each tile is denoted at the northwest corner of the tile. Therefore, for the single tile which represents the entire earth, the origin is set to lie at the North Pole and -180 degrees longitude, where you see Alaska." Last I checked, the North Pole is not in Alaska. More importantly, since this is a Mercator (coaxial cylindrical) projection, the North Pole must be at y = -Infinity! So clearly there is some cut-off value of latitude that's taken to be y = 0, presumably the one that makes the projected world map square. My tests tell me this value is latitude = 85.05113°, which would be quite a way north and a bit west of Alaska. The image that follows the above quoted text reflects this position more accurately, but insets the coordinate system. My tests also show that values north of this latitude will be mapped up to a point, in the gray area above the map tile. The cut-off at latitude = 90° is y = -74, so clearly a Mercator projection is no longer being used in this range (something nonlinear, though). Probably some people will be confused by this and/or duplicate the time I spent to determine the limits. I hope the Google team will correct the text to document the latitude limits and behavior in the polar regions with the default projection. It would also be better if the image was corrected, too, by moving the coordinate axes all of the way to the upper left corner. Thanks, -- Andy --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google Maps API" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/Google-Maps-API?hl=en -~----------~----~----~----~------~----~------~--~---
