[Proj] Web Mercator vs. Web Mercator Auxiliary Sphere

[Aaron Friesen]

Curiosity question ...

>From the Proj4 FAQ, for Web Mercator, the setting should be:

+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 \
                   +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs

I am having to deal with data in "Web Mercator Auxiliary Sphere",
as apparently defined by ESRI.

The WKT form spatialreference.org is:

PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",
    GEOGCS["GCS_WGS_1984",
        DATUM["D_WGS_1984",
            SPHEROID["WGS_1984",6378137.0,298.257223563]],
        PRIMEM["Greenwich",0.0],
        UNIT["Degree",0.0174532925199433]],
    PROJECTION["Mercator_Auxiliary_Sphere"],
    PARAMETER["False_Easting",0.0],
    PARAMETER["False_Northing",0.0],
    PARAMETER["Central_Meridian",0.0],
    PARAMETER["Standard_Parallel_1",0.0],
    PARAMETER["Auxiliary_Sphere_Type",0.0],
    UNIT["Meter",1.0],
    AUTHORITY["ESRI","102100"]]

How does the proj4 definition need to change to match?

Is setting b=6356752.314245 sufficient?

Aaron