[Proj] Conversion from WGS84 to UTM31

[Fabien Brachere]

Hello ,
I'm trying to convert data from my GPS to UTM31 coordinates and I use
something like that:

./cs2cs -v +init=epsg:4326 +to +init=epsg:23031
# ---- From Coordinate System ----
#Lat/long (Geodetic)
#
# +init=epsg:4326 +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
# +towgs84=0,0,0
#--- following specified but NOT used
# +ellps=WGS84
# ---- To Coordinate System ----
#Universal Transverse Mercator (UTM)
#       Cyl, Sph
#       zone= south
# +init=epsg:23031 +proj=utm +zone=31 +ellps=intl +units=m +no_defs
0.69315 42.785283333
311308.87       4739728.32 -208.92

The point is in spain and I use wms from icc
( http://shagrat.icc.es/lizardtech/iserv/ows? layer mtc50m which is
EPSG:23031 ) to see if my results are OK.
Unfortunaly the point is about 100 meters far from the real point (as
you can see here: http://map.brachere.net/stade.jpg ).

When I use circe2000 ( from french geographic institut :
http://www.ign.fr/affiche_rubrique.asp?rbr_id=1700&lng_id=FR#68081 ) or
transdat ( http://www.killetsoft.de/transdat.htm ) the conversion result
is:
311405.583 4739753.703 which is exactly where I was with my GPS ( on the
bridge, image http://map.brachere.net/stade_circe.jpg ).

Am I wrong with cs2cs parameters or is there another problem ?
Thank you for your attention.


-- 
Fabien Brachere <fabien.brachere at eikonex.net>
Eikonex