[Proj] NZGD2000 to NZGD49

Wed May 17 02:51:36 EDT 2006

Hi Anthony

Thanks for the tips.

I checked the epsg file and also read the man page for cs2cs which I should
have done first.

Using cs2cs -lp and -ld showed that nzgd49 and nzmg were available but
nzgd2000 was conspicuous by it's absence.

The epsg file had  the following for nzgd2000:

+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs

So I then tried the following:

cs2cs +proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs +to
+proj=nzmg +datum=nzgd49 +nadgrids=nzgd2kgrid0005

Which seemed to work (the first set of coordinates entered get droppped, but
I think I saw a bug logged for that already).

Using the following coordinates:

175.232739997 -37.3476467750

Gave me:

2708093.01      6425845.96

Whereas the LINZ site (
http://www.linz.govt.nz/rcs/linz/pub/web/root/core/SurveySystem/GeodeticInfo/CoordinateConversions/coordinateconversions/index.jsp

Gave me the following for the conversion:

175.232739997 -37.347646775         2708091.7091 6425845.7365

Which is 2 meters different in the x coordinate.

I then set PROJ_DEBUG to see what was going on and it said it couldn't open
/usr/local/share/proj/nzgd2kgrid0005, so I changed the command to add in the
.gsb on the end and got the correct answer (saw somehwre on the net with the
.gsb dropped off so incorrectly thought it was not needed).

cs2cs +proj=longlat +ellps=GRS80 +a=6378137 +rf=298.257222101 +to +proj=nzmg
+datum=nzgd49 +nadgrids=nzgd2kgrid0005.gsb
pj_open_lib(proj_def.dat): call fopen(/usr/local/share/proj/proj_def.dat) -
succeeded
pj_open_lib(proj_def.dat): call fopen(/usr/local/share/proj/proj_def.dat) -
succeeded

pj_open_lib(nzgd2kgrid0005.gsb): call
fopen(/usr/local/share/proj/nzgd2kgrid0005.gsb) - succeeded
NTv2 NZNAT    141x141: LL=(166,-48) UR=(180,-34)
pj_apply_gridshift(): failed to find a grid shift table for
                      location (0.0000000dW,0.0000000dN)
   tried: nzgd2kgrid0005.gsb
*       * 0.00
175.232739997 -37.3476467750
NTv2 - loading grid NZNAT
pj_open_lib(nzgd2kgrid0005.gsb): call
fopen(/usr/local/share/proj/nzgd2kgrid0005.gsb) - succeeded
pj_apply_gridshift(): used NZNAT
2708091.71      6425845.74 -0.00

Success, thank you.

I mainly use postgres and have data stored in NZGD2000/latlong(SRID=4167),
which I need to convert to  NZMG (SRID=27200)

How do I set up proj so that it uses the grid shift for this transform. Do I
have to add something somewhere to make it use it?
Postgres doco states if it is there it will use it but how???? cs2cs had a
lot of trouble, and using transform in postgres gives the same result as
cs2cs not finding the gsb file.

Simon

On 5/17/06, Anthony Dunk <AnthonyD at rocketmail.com> wrote:
>
> Hi Simon,
>
> I think the problem is that NZ datums are not defined in PROJ (I found
> the same was true of Australian datums). You will need to provide the
> ellipsoid parameters for these datums instead. i.e. +a=6378388.0
> +rf=297.0 for NZGD49 and +a=6378137.0 +rf=298.257222 for NZGD2000.
>
> So, to convert from NZGD200 Lat/Lon to NZGD49 Lat/Lon try this:
>
> cs2cs +proj=latlong +a=6378137.0 +rf=298.257222 +to +proj=latlong
> +a=6378388.0 +rf=297.0 +nadgrids=nzgd2kgrid0005
>
> Anthony.
>
> --- Simon O'Malley <simonom at gmail.com> wrote:
>
> > Hi
> >
> > I am trying to test the datum shift (using nzgd2kgrid0005.gsb file)
> > for
> > conversions between NZGD2000 and NZGD49(NZMG).
> >
> > I have downloaded the proj-datumgrid-1.3.zip file, and extracted
> > everything
> > under the nad directory.
> >
> > configured, make, and make install. However the gsb file does not get
> > copied
> > to /usr/local/share/proj
> >
> > I copied it across but postgis does not appear to use it i.e. my
> > transformed
> > coordinates are not correct, as verified by the linz website and
> > other
> > software that uses the grid file.
> >
> > I then tried to use cs2cs to validate it but all attempts at
> > specifying the
> > projections and datums gave me errors.
> >
> > I have tried multiple versions of:
> >
> > cs2cs +proj=latlong +datum=nzgd2000 +nadgrids=nzgd2kgrid0005 +to
> > +proj=nzmg
> > +datum=nzgd49
> >
> > After setting PROJ_DEBUG I get:
> >
> > pj_open_lib(proj_def.dat): call
> > fopen(/usr/local/share/proj/proj_def.dat) -
> > succeeded
> > Using from definition: proj=latlong datum=nzgd2000
> > nadgrids=nzgd2kgrid0005
> > Rel. 4.4.9, 29 Oct 2004
> > <cs2cs>:
> > projection initialization failure
> > cause: unknown elliptical parameter name
> > program abnormally terminated
> >
> > Tried upper and lower case NZGD2000, NZGD49, NZMG, latlong, longlat,
> > without
> > nadgrids???
> > Do I have to add an ellipsoid to the projection definitions for
> > cs2cs?
> >
> > The grid shift file does not appear to mentioned in any of the files
> > in
> > /usr/local/share/proj is that normal?
> >
> > Some pointers would be appreciated.
> >
> > Simon
> > > _______________________________________________
> > Proj mailing list
> > Proj at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/proj
>
>
>
>
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