[Proj] Portuguese Modified Grid - Datum 73
Jean-Claude REPETTO
jrepetto at free.fr
Wed Jun 23 08:11:48 EST 2010
Le 23/06/2010 14:41, Roger Oberholtzer a écrit :
>
> "+proj=tmerc " // Projection
> "+ellps=intl " // Spheroid
> "+k=1.0 " // Scale factor at central meridian
> "+x_0=180.598 " // False easting
> "+y_0=-86.98999999999999 " // False northing
> "+lon_0=-8.131906111111112 " // Longitude of central meridian
> "+lat_0=39.66666666666666 " // Latitude of origin
> "+towgs84=0,0,0,0,0,0,0 "
> "+no_defs"
>
> With test locations, I have a rather large error.
>
> Reference point (Santa Cruz):
>
> Latitude: 41.6743830556 Longitude: -8.3312663889 (WGS84)
> Easting: -16493.683 Northing: 222799.692
>
> Using the above definition, I get this:
>
> Easting: -16421.042 Northing: 222981.401
Hello Roger,
I am using these parameters in ttMaps :
+proj=tmerc +lat_0=39.66666666666666 +lon_0=-8.131906111111112 +k=1
+x_0=180.598 +y_0=-86.98999999999999 +ellps=intl
+towgs84=-239.749,88.181,30.488,0.263,0.082,1.211,2.229 +units=m +no_defs
The result is :
-16496.92 222796.31
that is far better than with your parameters.
Obviously your +towgs84 parameter is wrong, since the datums are different.
Jean-Claude
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