[Proj] New Zealand Map grid projection

[Frank Warmerdam]

On 11-03-27 08:26 PM, Claire Castellazzi wrote:
> Hi,
>
>
> I've got a problem with the results of the NZMG projection.
>
> Using proj 4.7.1 (23 sept 2009), I got :
>
>  >proj -I +proj=nzmg
>
> #2864916.8 6160570.9
>
> #177d8'19.853"E39d41'14.816"S
>
>
> But when I check my results with the Land Information New Zealand (LINZ)
>
> /_http://www.linz.govt.nz/geodetic/conversion-coordinates/online-conversion-service/converter/index.aspx_/
>
>
> I got :
>
> # New Zealand Map Grid Northing Easting : 6160570.9 2864916.8
>
> # World Geodetic System 1984 Latitude Longitude : 39 41 08.483 S 177 08 20.625 E

Claire,

Above you did not specify a datum for your NZMG projection and by default
the proj command is not changing datum.  What you want, apparently is:

cs2cs +proj=nzmg +datum=nzgd49 +to +proj=latlong +datum=WGS84
2864916.8 6160570.9
177d8'20.573"E	39d41'8.543"S 18.928

Things are still off by a fraction of a second, but much closer than you
were getting.  Note that the internal definition of +datum=nzgd49 is

   +ellps=intl +towgs84=59.47,-5.04,187.44,0.47,-0.1,1.024,-4.5993

I don't know what definition LINZ uses for NZGD49 - perhaps something
more accurate or even a grid shift based file?

Best regards,
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