[postgis-users] Coordinate transformation problem

[Guido Lemoine]

Are you sure your Belgian Lambert 1972 has SRID 31370, and not 31300??

Guido Lemoine

 srid  | auth_name | auth_srid | srtext |  proj4text
-------+-----------+-----------+--------+-----------
 31300 | EPSG      |     31300 |
 
PROJCS["Belge 1972 / Belge Lambert 72",GEOGCS["Belge 
1972",DATUM["Reseau_National_Belge_1972",
SPHEROID["International 1924",6378388,297,AUTHORITY["EPSG","7022"]],
AUTHORITY["EPSG","6313"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4313"]],
PROJECTION["Lambert_Conformal_Conic_2SP_Belgium)"],
PARAMETER["standard_parallel_1",49.83333333333334],
PARAMETER["standard_parallel_2",51.16666666666666],
PARAMETER["latitude_of_origin",90],
PARAMETER["central_meridian",4.356939722222222],
PARAMETER["false_easting",150000.01256],
PARAMETER["false_northing",5400088.4378],
UNIT["metre",1,AUTHORITY["EPSG","9001"]],
AUTHORITY["EPSG","31300"]]
                                                                                                          

+proj=lcc +lat_1=49.83333333333334 +lat_2=51.16666666666666 +lat_0=90 
+lon_0=4.356939722222222
+x_0=150000.01256 +y_0=5400088.4378 +ellps=intl +units=m +no_defs


Arnaud Lesauvage wrote:

> Hi list !
>
> I am trying to convert data from Belgian Lambert 1972 (SRID 31370) to 
> WGS84 UTM (zone 31N) (SRID 32631).
> The result of Transform(my_lambert_geom,32631) gives my a noticeably 
> misplaced result.
> The data is approximatively shifted of 100 meters !
>
> (see attached picture, grey is from the Lambert dataset, red is from 
> the UTM31N dataset, blue is the UTM31N data shifted to fit to the 
> Lambert data)
>
> The Lambert data comes from the Belgian Register, and has a .prj file 
> attached to it. I checked the .prj, and it corresponds to what I can 
> see in my spatial_ref_sys table.
> The WGS84 UTM31N data comes from TeleAtlas (I have confirmation that 
> it is in UTM 31N).
>
> How can I explain this shift ? I understand that converting conic to 
> geodetic projections implies some distortion, but 100 meters is quite 
> huge !
> What is wrong here ?
>
> Thanks for your help !
> -- 
> Arnaud
>
> ------------------------------------------------------------------------
>
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