[Proj] WGS84 to ED50

Roger Oberholtzer roger at opq.se
Mon Nov 19 09:50:17 EST 2007

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.

As an example, I have (via the C API):

fromProj = pj_init_plus(
			"+proj=latlong "
			"+ellps=WGS84 "

toProj = pj_init_plus(
			"+proj=utm "
			"+ellps=intl "
			"+k=0.999600 "
			"+x_0=500000.0 "
			"+y_0=0.0 "
			"+zone=30 "
			"+units=m "

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

Granted the difference is 1.489 meters. But at other locations it can be
a couple of meters away. The +towgs84 parameters cane from an e-mail
from Karel Cech on this list. Using these did improve the my values. But
I am not sure the values are correct.

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 =
 Coordinate transformation from WGS84 to mapping frame datum
    dX = 125.098545; dY = 76.000054; dZ = 156.198703; f =
    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 =
 false easting = 500000.000000 m; false northing = 0.000000 m;

Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Kapellgränd 7
P.O. Box 4205
SE-102 65 Stockholm, Sweden

Office: Int +46 8-615 60 20
Mobile: Int +46 70-815 1696

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