[Proj] WGS84 to ED50

[Oscar van Vlijmen]

> From: Roger Oberholtzer
> Date: Fri, 28 Dec 2007 19:44:18 +0100
> Subject: Re: [Proj] WGS84 to ED50

>>> Is anyone using proj to convert WGS84 latitudes and longitudes into ED50
>>> (Spain and Portugal) northings and eastings?

>>> 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

>>> 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;

> Your answer is not too late. I have not sorted this issue. What exactly
> did you change to obtain your results? Which angles were in radians
> instead of arc seconds? Was there anything else?

The rotation angles, so in effect only R3.
If you compare simple transforms (sines/cosines in the rotation matrix are
the same as the angles in rad), then coordinate frame has negated angles
compared to position vector.
If you want to do exact (but still first-order Helmert) transforms, then
you'll have to use a specialized datum transformation tool. In the case at
hand differences will emerge starting from the 5th decimal in
easting/northing. So you might as well use PROJ's simple transform.