[Proj] New Zealand grid?

Hamish hamish_nospam at yahoo.com
Thu Jul 7 01:04:54 EDT 2005

> >> I just noticed the new datum grid files (v1.3) that add the New
> >> Zealand grid.  I put these in the proj_src/nad folder, reconfigure,
> >> make and install, but I don't see any indication that the New
> >> Zealand grid file has been incorporated into proj - nothing
> >> installed in share/proj, and I can't tell if it's added to the
> >> library in some way.
> >>
> >> Is this a lark?  Or did I miss something to install this file
> >> (nzgd2kgrid0005.gsb)?
> >
> > I see I neglected to commit a change to the nad/Makefile.am and
> > nad/Makefile.in for installing .gsb files.  I have done so now.
> >
> > In the meantime you can just copy the .gsb file to /usr/local/share/
> > proj manually.
> So the gsb is something that proj knows about, and nothing is  
> generated from it (like for the lla files)?

It's the NTv2 binary grid, you can use it directly. An ASCII version of
the grid is available from the LINZ website if you want it.

The NZ binary grid is also integrated in GRASS 5.4 and newer (stored in
$GISBASE/etc/nad/) and available as a grid transform option if you use
the nzgd49 datum. NZGD49 is usually used with the nzmg projection or
older lat/lon surveys. This grid file is useful for converting NZGD49
datum to the NZGD2000 datum (nzgd2k ~ wgs84) which is used with the new
NZTM projection. NZGD2k is a dynamic datum which tries to deal with the
fact that one half of the country is moving 5cm/year in the opposite
direction from the other half. Currently tagged at ".2000" IIRC.

NZMG & NZTM are EPSG codes 27200 and 2193, respectively.

In GRASS 6.1-cvs from the last few weeks you can use g.proj to get
working projection parameters which can be fed into cs2cs.

e.g. for NZMG:
G6.1> g.proj -jf
+proj=nzmg +lat_0=-41.0000000000 +lon_0=173.0000000000
+x_0=2510000.0000000000 +y_0=6023150.0000000000 +a=6378388 +rf=297
+no_defs +nadgrids=$GISBASE/etc/nad/nzgd2kgrid0005.gsb

If not in /usr/share/proj/ or wherever other PROJ4 grids are stored
either put it there or supply full path to the file, as GRASS now does,
and it should work without any further effort.


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