[Proj] EPSG:28992 to EPSG:23031 conversion

[Mikael Rittri]

I looked in the EPSG database and found three transformations that could be useful. 

Name               | Code | Accuracy | Parameters for cs2cs 	
ED50 to WGS 84 (1) | 1133 |   10 m   | +towgs84=-87,-98,-121
ED50 to WGS 84 (2) | 1134 |    6 m   | +towgs84=-87,-96,-120
ED50 to WGS 84 (32)| 1999 |    3 m   | +towgs84=-83.11,-97.38,-117.22,0.005693,-0.04469,0.04428,1.218

(I am not sure what EPSG means by "Accuracy".)

The transform (1) is the same as Paul Kelly used. The Area of Use seems to be all 
countries in Europe where ED50 is defined except Great Britain and Ireland 
(namely "Austria; Belgium; Denmark; Finland; Faroe islands; France; Germany (west); 
Gibraltar; Greece; Italy; Luxembourg; Netherlands; Norway; Portugal; Spain; Sweden; 
Switzerland.") I could reproduce Paul's result, which gave a horizontal error 
of 2.11 m compared to your official result.  

The transform (2) has an Area of Use given as "Austria; Denmark; France; Germany (west); Netherlands; Switzerland."
When I tried it on your example, I got the result 

530199.428   5708616.032   0.738

with a horizontal error of 0.28 m. 

The transform (32) has an Area of Use given as "Netherlands - offshore North Sea."
When I tried it, I got the result 

530200.258   5708615.921   -11.560

with a horizontal error of 0.80 m. 

The source for (1) and (2) is given as "U.S. Defense Mapping Agency TR8350.2 September 1987," 
and the source for (32) is given as "Nederlandse Aardolie Maatschappij (NAM)."

Best regards,

Mikael Rittri
Carmenta AB
Box 11354
SE-404 28 Göteborg
Visitors: Sankt Eriksgatan 5
SWEDEN
Tel: +46-31-775 57 37
Mob: +46-703-60 34 07 
mikael.rittri at carmenta.com
www.carmenta.com

-----Original Message-----
From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of Paul Kelly
Sent: den 8 oktober 2008 23:33
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] EPSG:28992 to EPSG:23031 conversion

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,-0.406857330322398,0.3507326765425
>>> +63,-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
>> 
>> _______________________________________________
>> Proj mailing list
>> Proj at lists.maptools.org
>> http://lists.maptools.org/mailman/listinfo/proj
>> 
>> 
>
>
> --
> Bart van den Eijnden
> OSGIS, Open Source GIS
> bartvde at osgis.nl
> http://www.osgis.nl
>
> _______________________________________________
> Proj mailing list
> Proj at lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/proj
>
>
_______________________________________________
Proj mailing list
Proj at lists.maptools.org
http://lists.maptools.org/mailman/listinfo/proj