[PROJ] Helmert and coordinate convertion question

[Søren Holm]

Hi

I'm scratching my head here.

How do I convert the projected coordinates from the etmerc step into 
cartessian coordinates for the helmert step ?

cct +proj=pipeline +step +proj=etmerc +ellps=GRS80 +lat_0=0 +lon_0=20.25 
+k=1 +x_0=150000 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m 
+no_defs +step +proj=cart +ellps=GRS80 +step +proj=helmert 
+convention=coordinate_frame


Thanks in advance.

/Søren Holm