[Proj] Convert a planetographic latitude to a planetocentric latitude

[Jean-Christophe Malapert]

Hello,

I am quite new to the use of  Proj4. I spend a few days to investigate a
problem but I have no clue how to solve it. So that's why I am writing to
you.  I hope you will be able to answer me.

I have 2 different CRS for the same planet : one is based on the sphere (CRS1,
radius=3396190) and another one based on the ellipse (CRS2, a=3396190
b=3376200). When I give the (longitude, latitude) in the CRS1 as inputs (
planetocentric latitude = planetographic latitude), I want to get the
planetographic latitude expressed in the CRS2. So, I wrote the following
command :
cs2cs +proj=latlong +a=3396190 +b=3396190 +to +proj=latlong +a=3396190
+b=3376200
> 0 80  # longitude latitude

I get the following result "0dE 80dN 0.000" . The latitude should change
but it is not the case !!! Should I add some options ?  Is it possible to
do this kind of transformation with proj4 ?

Thanks in advance,
Jean-Christophe
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