[Proj] wrong values for shift utm ed50 to utm wgs84

[Markus Neteler]

On Thu, May 27, 2004 at 08:06:56AM +0200, Christoph Dohmen wrote:
> Hi all,
> 
> I have to translate several values from utm ed50 to utm wgs84. I tried this 
> with several tools and got different values :-( And especially using cs2cs I 
> got definitly _wrong_ values. Just an example:
> 
> values to translate as metre values from zone 32 north in ed50:
> 488000 E 
> 5902000 N
> 
> using the demo-version of transdat I get the following:
> 487916.915498 E 
> 5901796.048890 N
> 
> using the online-tool from http://www-ipf.bau-verm.uni-karlsruhe.de/cgi-bin/
> trafo.tcl I get:
> 487921.76 E
> 5901788.00 N
> 
> and using cs2cs (from proj 4.4.8) I get:
> 488000.00 E
> 5902000.00 N
> with the params: cs2cs +proj=utm +ellip=intl +to +proj=utm +ellip=WGS84 
> +datum=WGS84  << EOF
> > 488000 5902000
> > EOF

It should be ellps, not ellip, I think.
Hint: Use the -v flag to see which parameters are really used.
 
> using cs2cs +proj=utm +a=6378388.0 +b=6356911.94613 +zone=32 +to +proj=utm 
> +ellps=WGS84 +zone=32 << EOF with the same values result in:
> 488000.36 E
> 5901787.27 N
> 
> and cs2cs -v +init=epsg:23032 +to +init=epsg:32632 << EOF for the above 
> mentioned point results also in:
> 488000.36 E
> 5901787.27 N
> 
> >From several sources I read the there should be an offset in germany from 
> round about -80m east and -200m north. Those values are 'nearly' calculated 
> by the first two tools. But using cs2cs there is an offset of +0.36m east and 
> -212.73m north. The northing offset seems to look allright but the easting 
> offset must be wrong.
> 
> So, what is the mistake I made? Wrong params for cs2cs??
> Can anyone help me or even just give me a hint how to translate utm ed50 to 
> utm wgs84?

It seems that you are missing the ED50 Datum (here the "whole country" Potsdam datum):

cs2cs -v +init=epsg:23032 +towgs84=598.1,73.7,418.2,0.202,0.045,-2.455,6.70 +to +init=epsg:32632
# ---- From Coordinate System ----
#Universal Transverse Mercator (UTM)
#       Cyl, Sph
#       zone= south
# +init=epsg:23032 +towgs84=598.1,73.7,418.2,0.202,0.045,-2.455,6.70
# +proj=utm +zone=32 +ellps=intl +units=m +no_defs
# ---- To Coordinate System ----
#Universal Transverse Mercator (UTM)
#       Cyl, Sph
#       zone= south
# +init=epsg:32632 +proj=utm +zone=32 +ellps=WGS84 +datum=WGS84 +units=m
# +no_defs +towgs84=0,0,0
#--- following specified but NOT used
# +ellps=WGS84
488000 5902000
487930.33       5901554.44 930.44


You may want to select the appropriate Potsdam datum for your zone.

Hope this helps

 Markus

-- 
Markus Neteler     <neteler itc it>       http://mpa.itc.it
ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18        -       38050 Povo (Trento), Italy