[Proj] Converting NZMG -> Lat Long

[Hamish]

Hamish wrote:
> FWIW, from a GRASS-GIS NZMG location using the 7-parm transform (same as
> "proj -ld" shows) I get the following for the cs2cs "from" part:

> GRASS 6.3> g.proj -jf
> +proj=nzmg +x_0=2510000.0000000000 +y_0=6023150.0000000000 +a=6378388 +rf=297 +no_defs +towgs84=59.47,-5.04,187.44,0.47,-0.1,1.024,-4.5993 +to_meter=1.0

...
> using +datum=nzgd49 should give this part:  ("proj -ld")
>    +towgs84=59.47,-5.04,187.44,0.47,-0.1,1.024,-4.5993
> 
> but perhaps not the needed false eastings and northings?? (+x_0 and
> +y_0) same for +a and +rf??

+a and +rf are supplied by +ellps=intl of course,

$ proj -le | grep intl
     intl a=6378388.0      rf=297.          International 1909 (Hayford)


Hamish