[Proj] Google Mercator Projection

[Jose Gonçalves]

The formula for "Google Mercator" Y coordinate is:

6378137 * LN ( TAN ( PI / 4.0 + LAT / 2.0 ) )

For LAT=52.4827802220782 you get 6887893.49, which is what you are obtaining
with proj.
The other value is some 30 km smaller. May be it was calculated with the
actual Mercator projection of the ellipsoid.

Regards

José Gonçalves



2011/8/4 zagot <maurelio at live.it>

> Hi to All,
> this is an oldie, but i cannot seem to find a solution.
> When i want to do a transform on a wgs84 to google/bing the y coordinate
> shifts.
>
> I have read this  variuos post and this official note:
>
> http://trac.osgeo.org/proj/wiki/FAQ#ChangingEllipsoidWhycantIconvertfromWGS84toGoogleEarthVirtualGlobeMercator
>
> ...so I tried adding +nadgrids=@null like i read, but with this example:
>
> from ..."+proj=latlong +datum=WGS84";
>
> to... "+proj=merc +a=6378137 +b=6378137 +lat_t1=0.0 +lon_0=0.0 +x_0=0.0
> +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs"
>
> i have this result -626172.1357121646,  6887893.4928337997
>
> in the result y differ from correct value:6853955.508199729 (with Proj.NET
> the result is correct)
>
> ..seems adding +nadgrids=@null  have no effect
>
> what's I wrong?
>
> thanks in advance
>
> sorry for my english
> thanks
>
>
> --
> View this message in context:
> http://osgeo-org.1803224.n2.nabble.com/Google-Mercator-Projection-tp6651663p6651663.html
> Sent from the PROJ.4 mailing list archive at Nabble.com.
> _______________________________________________
> Proj mailing list
> Proj at lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/proj
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20110804/d27dbf40/attachment.html>