[Proj] Problem overlaying georeferenced images in Google,Maps(projection problem!)

[Frank Warmerdam]

Eric Miller wrote:
> Yes, Google maps uses a spherical model rather than ellipsoidal (hence, +a == +b in the destination coordinate system).  So, it's not really WGS84.  However, my understanding is that GMaps projection assumes there isn't any difference.  So, source coordinates should be converted to Geodetic on the WGS84 ellipsoid/datum and then projected onto the Google Mercator "WGS84" sphere ignoring the fact that the models are really different.  So, the +towgs84 parameter on the destination should probably be defined as +towgs84=0,0,0.

Folks,

I haven't followed this issue closely, but please be sure you are aware of:

 
http://trac.osgeo.org/proj/wiki/FAQ#ChangingEllipsoidWhycantIconvertfromWGS84toVirtualEarthMercator

Best regards,
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