On Nov 30, 7:15 pm, PHL <[EMAIL PROTECTED]> wrote: > On Nov 30, 8:00 pm, bratliff <[EMAIL PROTECTED]> wrote: > > > Also, I have made improvements to: > > > http://www.polyarc.us/usgs > > > It requires the browser to support: > > > JavaScript > > DHTML > > DOM > > > It produces a WMS tile layer overlay for Google's static map. The > > alignment improves in larger numbered zoom levels. EPSG:4326 is > > different than Google's Mercator projection but nothing else is > > available. > > Is that the reason for the few degrees shift towards North in the WMS > layer? > (At least that’s what happens in my Firefox 3 at the moment).
I do not know the specifics of EPSG:4326 except to say it is not identical to Google's Mercator projection. I suspect it is a Euclidian projection. At zoom levels 1 through 4, each tile spans a large number of degrees of Latitude. The discrepency is very noticable. At zoom levels 7 through 17, each tile spans fewer degrees of Latitude. The discrepency will gradually shrink. If the USGS server supports something like Google's Mercator projection, I am not aware of it. Slicing it into tiles masks the difference. Google does something similar with their GroundOverlays. By using your own span algorithm to choose the zoom level for Google's static map, you know it will be identical to the zoom level you choose for your image. Otherwise, you may discover the zoom levels differ by one in some borderline cases. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
