[PROJ] Pipeline: Cartesian transform to change from ellipsoid to sphere

[Laura, Jason R]

List,

I have a set of body-centered body-fixed coordinates that were computed with an ellipsoid of +a=3396190 +b=3376200. I am attempting to reproject these into a spherical datum (+R=3396190) using the pipeline syntax. For example,

        +proj=pipeline +units=m
        +step +proj=cart +a=3396190 +b=3376200
        +step +proj=cart +R=3396190

Which is failing with a unit warning. I suspect I am missing something basic.

I have looked at the geodesic -> Helmert -> geodesic transformation tutorial, but I am clearly misunderstanding something (https://proj.org/en/9.3/tutorials/EUREF2019/exercises/pipelines.html#geodetic-helmert-geodetic)

Looking at these docs, I tried:

        +proj=pipeline
        +step +proj=cart +a=3396190 +b=3376200
        +step +proj=helmert +z=19990 +convention=position_vector
        +step +inv +proj=cart +R=3396190

But I get an invalid latitude error (which I believe means I am misspecifying the input system).

Any suggestions appreciated,
Jay
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20240812/25d47c71/attachment.htm>