[Proj] Portuguese Modified Grid - Datum 73

[Jean-Claude REPETTO]

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