[GRASSLIST:1701] v.proj bug?

David Orme d.orme at imperial.ac.uk
Thu Nov 6 10:57:24 EST 2003


I e-mailed a while back about a problem with s.proj - I've encountered 
something similar in v.proj.

I have a raster dataset in the old New Zealand South Island grid 
(Transverse Mercator: central meridian 171.5E, latitude of origin 44S, 
scale 1, false easting 500000, false northing 500000, units yards, 
ellipse international). This projection is included in ArcMAP and when 
I compare a graticuled map in ArcMAP to (coarse scaled) printed grid of 
the raster  for the dataset, there is a very close match.

I've tried to set up a GRASS location to match this (I've appended the 
PROJ_INFO) and downloaded the DCW vector coastline to use as a base 
map. I imported this into a latlong location and v.proj'd it across and 
found that the coordinates did not match ArcMAP. I've picked two South 
Island locations as test sets  - Cape Providence (bottom left) and the 
tip of Farewell Spit (top right). These have the following lat longs 
(in s.in.ascii format and cs2cs):

166:27:28.0E 46:00:55.0S Cape_Providence
173:01:05.1E 40:33:28.8S Farewell_Spit

166d27'28.0E 46d00'55.0S
173d01'05.1E 40d33'28.8S

In ArcMAP (and through a separate NZ grid application for Classic Mac 
and approximately from my printed grid) these have the NZ SI 

72976E 241337N Cape_Providence
640603E 916716N Farewell_Spit

I've run the vector file and these two coordinates through cs2cs: the 
vector file imported through cs2cs and the e00 imported through v.proj 
overlie exactly and the coordinates of the points out of cs2cs are:

119772.29E 288333.97N Cape_Providence
687425.44E 963732.29N Farewell_Spit

The cs2cs arguments used were:

cs2cs +proj=latlong +ellps=clrk66 +to +proj=tmerc +lat_0=44S 
+lon_0=171.5E +x_0=500000 +y_0=500000 +ellps=intl +units=yd

I have also tried moving the units argument to earlier in the argument 

cs2cs +proj=latlong +ellps=clrk66 +to +proj=tmerc  +units=yd +lat_0=44S 
+lon_0=171.5E +x_0=500000 +y_0=500000 +ellps=intl

This _does_ change the coordinates, but unfortunately not to match 

109519.78E 263652.58N Cape_Providence
628581.82E 881236.81N Farewell_Spit

Any suggestions?

David Orme

New Zealand South Island Location PROJ_INFO:

name: Transverse Mercator
proj: tmerc
ellps: international
a: 6378388.0000000000
es: 0.0067226700
f: 297.0000000000
lat_0: -44.0000000000
lon_0: 171.5000000000
k_0: 1.0000000000
x_0: 500000.0000000000
y_0: 500000.0000000000

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