[Proj] Incorrect translations to the Gauss-Boaga system

[Gino Lucrezi]

I am currently using version 4.4.8 of the proj4 libraries. I mostly use them from within PostGIS, but I get the same results calling them on a stand-alone basis.

One widely used coordinate system here in Italy is Gauss-Boaga,
corresponding to EPSG codes 26591 and 26592.

So, I often have to convert between Gauss Boaga and UTM 33 (epsg:23033)

Here are the results for two known points:
cs2cs +init=epsg:26592 +to +init=epsg:23033 -v <<EOF
2413000.0000 4669000.0
2389238.48 4690935.27
EOF

# ---- From Coordinate System ----
#Transverse Mercator
#       Cyl, Sph&Ell
# +init=epsg:26592 +proj=tmerc +lat_0=0 +lon_0=2.54766666666667 
+k=0.999600
# +x_0=2520000 +y_0=0 +ellps=intl +pm=rome +units=m +no_defs
# ---- To Coordinate System ----
#Universal Transverse Mercator (UTM)
#       Cyl, Sph
#       zone= south
# +init=epsg:23033 +proj=utm +zone=33 +ellps=intl +units=m +no_defs
393000.00       4669000.00 0.00
369238.48       4690935.27 0.00

The first point I could check on a map, and it should have been
393070 4669190 I used a good ruler, and I am sure I got this point with an error smaller than 10 metres.

The second point was converted using another (interactive) program, which is usually regarded as authoritative, and it resulted in 369301 4691118

In either case, the resulting point is about 200 metres off from the correct result.

I didn't modify the epsg file in any way.

Did I do anything wrong?

Gino Lucrezi
Penta Consulting Services Srl