[Proj] WGS84 to ED50

[Roger Oberholtzer]

On Mon, 2007-11-19 at 13:57 -0800, Hamish wrote:

> > The Applanix provides this information on their calculations:
> ...
> >  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;
> 
> 
> The above R3,f values makes me hesitate a little, but it may be that Applanix
> and Trimble are both preforming a less precise 3-term transform, while PROJ is
> doing a more precise 7-term transform. That would certainly explain a 1-4m
> error.

My understanding is that Applanix is doing a 7 parameter transform. What
I am unsure of is how to get proj to do the same. If it is the default,
then I am curious how the 7 parameters are specified. Are these the
values in the +towgs84 option? I have another library for this that is
using 7 config values for its 7 parameter transform, and I would expect
to see similar values in proj.

> Rather than trust either software or method implicitly, it would be better to
> judge the results based on published test points from the Spainish and/or
> Portuguese government mapping office, and double check the validity of the
> 7-terms params from an official document too. Depending on national convention,
> the +- signs of the terms may or may not be switched.

I have been trying to do just that. The person I am doing this for in
Madrid has provided the test values I am trying to duplicate. Anyone
know of an official source of test values for Spain?

-- 
Roger Oberholtzer

OPQ Systems / Ramböll RST
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