[Proj] Offset when converting coordinates from ESRI:31700 to EPSG:4326

[Adrian Popa]

Hello everyone,

I have a problem when converting coordinates from ESRI:31700 (Stereo 70)
to WGS84 (EPSG:4326). The coordinates I get from the conversion have an
offset from the original coordinate of about 50m. Here's an example:

Original coordinates (Stereo 70):  587486.770, 326878.452
Converted coordinates (WGS84): 26.099032,44.436575
Real coordinates (converted from Stereo 70 with Global Mapper and
checked with a GPS unit): 26.097414, 44.436335

For the conversion I'm using cs2cs Rel. 4.7.1, 23 September 2009 on
Ubuntu 10.04.

My ESRI/EPSG definitions are as follows:

EPSG:
# Dealul Piscului 1970/ Stereo 70 (deprecated)
<31700> +proj=sterea +lat_0=46 +lon_0=25 +k=0.99975 +x_0=500000
+y_0=500000 +ellps=krass +units=m +no_defs <>
# WGS 84
<4326> +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs <>

ESRI:
# Dealul Piscului 1970/ Stereo 70
<31700> +proj=stere +lat_0=46 +lon_0=25 +k=0.999750 +x_0=500000
+y_0=500000 +ellps=krass +units=m +no_defs  no_defs <>

The command line I'm using is:
$ echo 587486.770 326878.452 | cs2cs +init=esri:31700 +to
+init=epsg:4326 -f '%0.6f'
26.099032    44.436575 0.000000
$ echo 587486.770 326878.452 | cs2cs +init=epsg:31700 +to
+init=epsg:4326 -f '%0.6f'
26.098934    44.436629 0.000000

I've read that there is a small difference between stere and sterea
projections, and sterea should give a better approximation, but I've
tried with both projections and I still get the ~50m offset.

Can anybody clue me in as to what I'm doing wrong? I must be missing
something, but I don't know what (I'm somewhat of a noob when it comes
to map projections).

P.S. The definition for Stereo 70 that I received with my data looks
consistent with the definition inside proj4:

PROJCS["Stereo_70",GEOGCS["GCS_Dealul_Piscului_1970",DATUM["D_Dealul_Piscului_1970",SPHEROID["Krasovsky_1940",6378245,298.3]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Double_Stereographic"],PARAMETER["False_Easting",500000],PARAMETER["False_Northing",500000],PARAMETER["Longitude_Of_Origin",25],PARAMETER["Scale_Factor",0.99975],PARAMETER["Latitude_Of_Origin",46],UNIT["Meter",1]]


Thanks,
Adrian
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