[Proj] Portuguese Modified Grid - Datum 73

[Jose Gonçalves]

2010/6/23 Roger Oberholtzer <roger at opq.se>

> On Wed, 2010-06-23 at 15:11 +0200, Jean-Claude REPETTO wrote:
> > +towgs84=-239.749,88.181,30.488,0.263,0.082,1.211,2.229
>


Those +towgs84 parameters convert Datum73 to WGS84 with errors of the order
of 1 meter. I have a datum shift grid file to convert from Datum 73 to
ETRS89 available on the address:

http://www.fc.up.pt/pessoas/jagoncal/coordenadas/pt73_e89.gsb


You can convert ETRS89 long-lat to projected Datum73 with the follwoing
command line (errors in general smaller than 10 cm) :

cs2cs +init=epsg:4258 +towgs84=0,0,0 +to +init=epsg:27492
+nadgrids=pt73_e89.gsb


The WGS84 coordinates of your test point are not very accurate.


Regards

José A. Gonçalves
University of Porto, Portugal
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