[Proj] WGS84 to ED50

[Oscar van Vlijmen]

A bit late reply, but might be still of some use....

> From: Roger Oberholtzer
> Date: Mon, 19 Nov 2007 15:50:17 +0100
> Subject: [Proj] WGS84 to ED50
> 
> Is anyone using proj to convert WGS84 latitudes and longitudes into ED50
> (Spain and Portugal) northings and eastings?
> 
> My attempts get me to within a couple of meters of values calculated by
> Trimble and Applanix (which are within a mm of each other). I did ask a
> question about this a while back and got some answers that improved my
> values by some 100 meters. But I never did get the values I need. So I
> am trying again.
> 
.....

> When I transform:
> 
> lat=42.87645687 lng=-4.88298199 alt=0.00000000
> 
> I get Easting=346318.770 Northing=4749022.461
> 
> but I need Easting=346319.686 Northing=4749023.634
> 
.....
> 
> As Applanix and Trimble provide the same values for Spain (the ones I am
> trying to get from proj), they must be using an existing and agreed upon
> method. I would be surprised if proj couldn't do the same, if I could
> just figure out how to tell it to do so!
> 
> The Applanix provides this information on their calculations:
> 
> Mapping frame datum: ED50_ESPA?A ; a = 6378388.000000; 1/f =
> 297.000000;
> Coordinate transformation from WGS84 to mapping frame datum
> dX = 125.098545; dY = 76.000054; dZ = 156.198703; f =
> 0.999991695369;
> R1 = 0.000000000000; R2 = 0.000000000000; R3 = -0.000005473550;
> sequence of the rotations: x,y,z,1
> Mapping frame projection : TM;
> central meridian = -3.000000 deg;
> latitude of the grid origin = 0.000000 deg; grid scale factor =
> 0.999600:
> false easting = 500000.000000 m; false northing = 0.000000 m;
> 

With these parameters - in the proper units - I get for x,y:
346319.6988, 4749023.4599 m
Differences with the 'needed' values:
dx = 0.013; dy = 0.174 m
I assumed an 'exact' first-order coordinate frame rotation model, order XYZ,
then scale.
I think the given rotation angles are in radians, so I converted them to arc
seconds.
Note that PROJ uses a position vector rotation model and a simple transform
method.