[Proj] Google Mercator Projection

Jose Gonçalves jagoncal at gmail.com
Thu Aug 4 09:10:51 EST 2011

You can't mix "+a=6378137 +b=6378137" and "+datum=WGS84".
The control +datum implies an ellipsoid, which will conflict with the
definition of the sphere. Presumably the behaviour of the program is to
consider the last to be specified.

The conversion from WGS84 geographic coordinates to Google Mercator in the
command line does not need CS2CS. It can be done with PROJ, since it doesn't
involve a datum transformation:

echo -5.625 52.4827802220782 | proj +a=6378137 +b=6378137 +proj=merc
-626172.14      6887893.49



> You have forgotten to specify the datum for the projected CRS :
> cs2cs +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 +datum=WGS84 +units=m
> +nadgrids=@null +no_defs
> -5.625 52.4827802220782
> -626172.14      6853979.30 0.00
> Jean-Claude
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