[Gdal-dev] Spherical Mercator using PROJ.4

[ronan.gdal]

I would like to use Spherical Mercator projection (the earth is a sphere model). 

My purpose is to produce raster for other software using Mercator projection Sphere formula : merc = ln( tan ( pi / 4 + L / 2 ) ).

My test have been using POSTGIS, entering following PROJ.4 parameters :
+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +k=1.0 +x_0=0 +y_0=0 +units=m +nodefs.

(a=WGS major axis, b=a (excentricity should be null); I've also tried b=0, +ellips=sphere ... always same result!).

Results looks like to be always Mercator ellipsoid projection formula, never SPHERE formula.

Is there any way to use PROJ.4 sphere formula ?

Thanks. 
Ronan

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