[Proj] EPSG:28992 to EPSG:23031 conversion

[Paul Kelly]

On Wed, 8 Oct 2008, Bart van den Eijnden (OSGIS) wrote:

> Hi Jean-Claude,
>
> I am using PROJ 4.4.9 so that should not be necessary or am I mistaken?

I think you are mistaken, but would be interested if you could explain 
your reasoning behind that understanding. There seems to be a lot of 
confusion about the differences in this area in PROJ 4.4.9 and it might 
help to understand what is causing this confusion.

Jean-Claude is indeed correct about the second transformation lacking 
datum transformation paramters. If I use +towgs84=-87,-98,-121 (a general 
solution for ED 1950 across Europe) with your command-line I get the 
output:
530201.420293435        5708616.572244617 1.595183260
which is much closer to the official results. I suspect if you found a 
datum tranformation set for ED 1950 specifically covering the Netherlands 
rather than Europe as a whole you could get very close. (The NIMA TR8350.2 
document might perhaps be useful here; I haven't looked.)

Best regards,

Paul

>
> Best regards,
> Bart
>
> Jean-Claude Repetto wrote:
>> bartvde at osgis.nl wrote :
>> 
>>> when I use PROJ.4 to do a conversion between EPSG:28992 (the Dutch
>>> national grid) and UTM zone 31 ED50 I get:
>>> 
>>> cs2cs -f %.9f +proj=sterea +lat_0=52.15616055555555
>>> +lon_0=5.38763888888889 +k=0.999908 +x_0=155000 +y_0=463000 +ellps=bessel
>>> +units=m
>>> +towgs84=565.2369,50.0087,465.658,-0.406857330322398,0.350732676542563,-1.8703473836068,4.0812 
>>> +no_defs +to +proj=utm +zone=31 +ellps=intl +units=m +no_defs
>>> 19465 394814
>>> 530108.861080788        5708613.329898705 -150.818087836
>>> 
>>> 
>>> Northing 5708615,754
>>> Easting 530199,479
>>> 
>>> so especially the difference in easting is too large.
>>> 
>>> Is there a logical explanation for this difference? TIA.
>> 
>> Hi Bart,
>> 
>> I think you have forgotten the +towgs84 parameters to do the WGS84 -> ED50 
>> transformation.
>> 
>> Jean-Claude
>> 
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>> 
>
>
> -- 
> Bart van den Eijnden
> OSGIS, Open Source GIS
> bartvde at osgis.nl
> http://www.osgis.nl
>
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