Adrian<br><br>The problem is that datum transformation is not being done. The coordinate system definition esri:31700 only considers the projection and not a datum transformation (e.g. +towgs84=...). There are different sets of datum shift parameters for datum Dealul_Piscului_1970. In the ArcGIS documentation I found the following:<br>
<br>dX=44.107 dY=-116.150 dZ=-54.648<br>dX=28.000 dY=-121.000 dZ=-77.000<br><br>You must include one of them it in the cs2cs command:<br><br>cs2cs +init=esri:31700 +towgs84=28,-121,-77 +to
+init=epsg:4326 -f '%0.6f'<br><br><br>Regards<br><br>José A. Gonçalves<br><br><br><br><div class="gmail_quote">2011/4/22 Adrian Popa <span dir="ltr"><<a href="mailto:adrian_gh.popa@romtelecom.ro">adrian_gh.popa@romtelecom.ro</a>></span><br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hello everyone,<br>
<br>
I have a problem when converting coordinates from ESRI:31700 (Stereo 70)<br>
to WGS84 (EPSG:4326). The coordinates I get from the conversion have an<br>
offset from the original coordinate of about 50m. Here's an example:<br>
<br>
Original coordinates (Stereo 70): 587486.770, 326878.452<br>
Converted coordinates (WGS84): 26.099032,44.436575<br>
Real coordinates (converted from Stereo 70 with Global Mapper and<br>
checked with a GPS unit): 26.097414, 44.436335<br>
<br>
For the conversion I'm using cs2cs Rel. 4.7.1, 23 September 2009 on<br>
Ubuntu 10.04.<br>
<br>
My ESRI/EPSG definitions are as follows:<br>
<br>
EPSG:<br>
# Dealul Piscului 1970/ Stereo 70 (deprecated)<br>
<31700> +proj=sterea +lat_0=46 +lon_0=25 +k=0.99975 +x_0=500000<br>
+y_0=500000 +ellps=krass +units=m +no_defs <><br>
# WGS 84<br>
<4326> +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs <><br>
<br>
ESRI:<br>
# Dealul Piscului 1970/ Stereo 70<br>
<31700> +proj=stere +lat_0=46 +lon_0=25 +k=0.999750 +x_0=500000<br>
+y_0=500000 +ellps=krass +units=m +no_defs no_defs <><br>
<br>
The command line I'm using is:<br>
$ echo 587486.770 326878.452 | cs2cs +init=esri:31700 +to<br>
+init=epsg:4326 -f '%0.6f'<br>
26.099032 44.436575 0.000000<br>
$ echo 587486.770 326878.452 | cs2cs +init=epsg:31700 +to<br>
+init=epsg:4326 -f '%0.6f'<br>
26.098934 44.436629 0.000000<br>
<br>
I've read that there is a small difference between stere and sterea<br>
projections, and sterea should give a better approximation, but I've<br>
tried with both projections and I still get the ~50m offset.<br>
<br>
Can anybody clue me in as to what I'm doing wrong? I must be missing<br>
something, but I don't know what (I'm somewhat of a noob when it comes<br>
to map projections).<br>
<br>
P.S. The definition for Stereo 70 that I received with my data looks<br>
consistent with the definition inside proj4:<br>
<br>
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]]<br>
<br>
<br>
Thanks,<br>
Adrian<br>
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</blockquote></div><br>