[Proj] Conversion from WGS84 to UTM31

[Martin Vermeer]

On Tue, 2006-02-28 at 13:55 +0100, Fabien Brachere wrote:
> Le mardi 28 février 2006 à 13:25 +0200, Martin Vermeer a écrit :
> > On Tue, 2006-02-28 at 11:42 +0100, Fabien Brachere wrote:
> > 
> > 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
> > 
> > Surely there must be a datum offset... UTM31 coordinates on the
> > international ellipsoid sounds like a terrestrial, non-geocentric datum,
> > even if the <23031> entry doesn't provide one. 100 m sounds about right.
> > 
> > - Martin
> 
> Thank you Martin, I think the datum is ED50 but I don't know how to
> apply the offset, with towgs84 parameter or a grid ? If yes, do you know
> where I can find the datum offset or the grid ?

Google is your friend...

dx = -84 m +/- 5 m
dy = -107 m +/- 6 m
dz = -120 m +/- 3 m

see http://www.asprs.org/resources/grids/07-2000-spain.pdf

- Martin

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