[GRASSLIST:4592] Re: Datum transform frustrations

[Joel Peter William Pitt]

Hamish wrote:

>>and for the destination map:
>>-PROJ_INFO-------------------------------------------------
>>name       : Transverse Mercator
>>datum      : nzgd2k
>>towgs84    : 0.000,0.000,0.000
>>proj       : tmerc
>>ellps      : grs80
>>a          : 6378137.0000000000
>>es         : 0.0066943800
>>f          : 298.2572221010
>>lat_0      : 0.0000000000
>>lon_0      : 173.0000000000
>>k_0        : 0.9996000000
>>x_0        : 1600000.0000000000
>>y_0        : 10000000.0000000000
>>-PROJ_UNITS------------------------------------------------
>>unit       : meter
>>units      : meters
>>meters     : 1.0
>>    
>>
>You might check against a test coordinate:
>
>Eastern entrance to Akaroa Harbour:
>
>NZMG projection w/ NZGD49 datum
>  2507512.60416667   5702150
>
>NZTM projection w/ NZGD2k datum
>  1597502.78125      5140557.1875
>
>Lat/Lon w/ WGS84 datum
>  172:58:08.07E      43:53:17.0925S
>
>
>(give or take a few meters)
>
>
>
>You should definitely get the LINZ vector coastline from NZTopoOnline: 
>  http://www.nztopoonline.linz.govt.nz
>
>(Uses Arc/Web so horribly slow and mostly unusable... but you can
>extract shape files eventually)
>
>those are provided in NZTM/gd2k and you can figure out what's right and
>what's wrong from there.
>  
>
Thanks Hamish :)

Okay, I extracted the region around Akaroa from NZTopoOnline and
overlaid it. One of my files was significantly off.

Now I have a slightly different (or maybe related) problem:
The projection co-ordinates match when I use "d.where -d -w"
for both nzmg and tmerc projections, but the longitude and
latitude is way off (approximately, if not exactly, the same for both):

172.96917306E       43.87039362S

When I use ArcMap it shows the same coordinates, but the correct
lat/long values.

Joel