Offset in WGS84 to UTM32 ED50 projection about proj HOT 10 CLOSED

Comment by warmerdam on 25 Mar 2009 15:56 UTC
What definitions are you using for ED50? I imagine this is a problem with the EPSG "init file" which may lack any information on how to transform ED50 to WGS84.

This is not a bug in PROJ.4, though it does tend to lead people astray.

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Comment by lcivik on 26 Mar 2009 12:14 UTC
I use code epsg:23032 for Geotools and Proj4, while I use code 82343 for
Oracle srid. All codes refers to this wkt

PROJCS[/ UTM zone 32N",GEOGCS
["ED50",
DATUM["European_Datum_1950",SPHEROID["International 1924",6378388,297,
AUTHORITY"EPSG","7022"],AUTHORITY["EPSG","6230"]],PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","
9122"]],AUTHORITY["EPSG","4230"]],
PROJECTION["Transverse_Mercator"],PARAMETER
["latitude_of_origin",0],PARAMETER["central_meridian",9],
PARAMETER
["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER
["false_northing",0],
UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY
["EPSG","23032"]].

The offset between GeoTools/Oracle and Proj4 is more than
100m.

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Comment by lcivik on 26 Mar 2009 12:15 UTC
Replying to warmerdam:

What definitions are you using for ED50? I imagine this is a problem with the EPSG "init file" which may lack any information on how to transform ED50 to WGS84.

This is not a bug in PROJ.4, though it does tend to lead people astray.

I use code epsg:23032 for Geotools and Proj4, while I use code 82343 for Oracle srid. All codes refers to this wkt

PROJCS[/ UTM zone 32N",GEOGCS ["ED50", DATUM["European_Datum_1950",SPHEROID["International 1924",6378388,297, AUTHORITY"EPSG","7022"],AUTHORITY[AUTHORITY"EPSG","8901"], UNIT9122"],AUTHORITY[PROJECTIONTransverse_Mercator?,PARAMETER "latitude_of_origin",0,PARAMETER[PARAMETER "scale_factor",0.9996,PARAMETER["false_northing",0, UNIT["EPSG","23032"].

The offset between GeoTools/Oracle? and Proj4 is more than 100m.

from proj.

Comment by lcivik on 26 Mar 2009 12:16 UTC

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Comment by warmerdam on 26 Mar 2009 15:25 UTC
I have checked and confirmed that the PROJ.4 EPSG init file does not by default contain datum shift values for ED50. This is almost certainly because the original EPSG database provides more than one option.

You need to decide on a datum shift transform you would like to use in your area and add it to the init file definition.

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Comment by lcivik on 26 Mar 2009 16:12 UTC
In epsg init file I found this entry
<23032> +proj=utm +zone=32 +ellps=intl +units=m +no_defs no_defs <>
Can you tell me what i should do in order to solve my problem? My area of interest covers only Italy.

Thanks.

Replying to warmerdam:

I have checked and confirmed that the PROJ.4 EPSG init file does not by default contain datum shift values for ED50. This is almost certainly because the original EPSG database provides more than one option.

You need to decide on a datum shift transform you would like to use in your area and add it to the init file definition.

from proj.

Comment by warmerdam on 27 Mar 2009 04:07 UTC
The following topic talks about how to define a towgs84 parameter. Getting the right values for ED50 is basically an effort in searching the web with google (possibly including the PROJ.4 mailing list archives), or reviewing the EPSG database in detail (an involved process IMHO).

http://trac.osgeo.org/proj/wiki/GenParms#towgs84-DatumtransformationtoWGS84

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Comment by lcivik on 27 Mar 2009 09:49 UTC
Replying to warmerdam:

The following topic talks about how to define a towgs84 parameter. Getting the right values for ED50 is basically an effort in searching the web with google (possibly including the PROJ.4 mailing list archives), or reviewing the EPSG database in detail (an involved process IMHO).

http://trac.osgeo.org/proj/wiki/GenParms#towgs84-DatumtransformationtoWGS84
Towgs84 parameter concerns the transformation from certain projection to WGS84. In my case i need the transformation from WGS84 (gps datum) to UTM32 ED50 (epsg code 23032). Actually, i think that trasformation given by proj4 is wrong.

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Comment by warmerdam on 27 Mar 2009 11:26 UTC
If you describe the ED50 datum with information on how it should be transformed to WGS84,then PROJ can use that information also to go the other way - from WGS84 to ED50.

I would like to stress that there are many possible transformations from ED50 to WGS84, and because it is impossible for PROJ to pick one that is certain to be right, it does not use any datum shift at all until you specify one. So, even if you use the EPSG init file, it is up to you to provide a datum shift value if you want one applied.

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Comment by rouault on 11 May 2009 22:16 UTC
Look at this : http://earth-info.nga.mil/GandG/coordsys/onlinedatum/CountryEuropeTable.html#

You might want to try then "+proj=utm +zone=32 +ellps=intl +units=m +towgs84=-87,-98,-121 +no_defs" which is the "Mean Solution". Or -97,-103,-120 which is "Sardinia (Italy)"

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