[Proj] WGS84 to ED50

Mon Nov 19 19:26:28 EST 2007

Hi everyone,

Clifford is right....this is an interesting thread.

Let me provide some documentation and some web-sites that 
may be able to aid in what you are trying to do.

ED50, and especially in Spain, parts of France, etc. is 
not fully defined in transformations between ED50 and 
WGS80 or ETRS.

The Spanish Gov't has various methods depending on regions 
(such as Catalin, Valencia, etc.) - so you can not apply 
one method of transformation over a region.

The Gov't worked on REGENTE to be able to transform 
between ED50 and ETRS. Which from my reading (it is in 
Spanish) is based on the NTv2 grid type files. This method 
will provide a higher accuracy in your transformation - 
but there will still be errors.

To compare co-ordinates using REGENTE between ED50 and 
ETRS, please see the following link:

http://www.ign.es/ign/es/IGN/calculadora_geodesica.jsp

You want to use option: ED50-ETRS89

For the reverse, use option ETRS89-ED50

For information on REGENTE the following are two good 
documents:

http://www.gfy.ku.dk/~iag/Spain_Sapporo_2003.pdf

The above was presented at the IUGG in Sapporo Japan in 
2003.

The following is a summary of methods used in transforming 
between ED50 and ETRS.

http://www.euref-iag.net/symposia/book2003/4-6.pdf

It is an interesting read.

Datum transformations are not simple. In many cases, the 
old networks were a series of triangulation networks tied 
together, yet each of these surveys were done at different 
accuracies and different times. Often over many years over 
a large area - take the Indian subcontinent for example.

I will do some more research and see what tools, both 
provided by the Spanish Gov't (often it is just a simple 
request for files in a specific format - such as in South 
Africa - for files in NTv2), or by contacting local 
agencies and companies.

I hope the above information clears up some questions 
about the problems of assuming something as simple as 
7-parameter transformation for such a large area.

If you have any questions, feel free to contact me.

Kind regards,
Dean

On Mon, 19 Nov 2007 16:43:39 -0600
  "Clifford J Mugnier" <cjmce at lsu.edu> wrote:
> I have been reading this thread with some amusement, as 
>datum shifts are only a compromise to begin with, and 
>attempting to achieve better than 1-2 meters with even a 
>7-parameter transformation is a totally unreasonable 
>expectation.  The original data for the classical datum 
>is not that good!
> 
> Matching another transformation is a reasonable 
>expectation, but it could be (likely), that the "client" 
>is attempting to match actual observations with 
>Trimble/Applanix gear working directly in WGS84 rather 
>than a Trimble/Applanix algorithm!  European Datum 50 
>(ED50) was "cooked up" in 1950 by Geodesists at the U.S. 
>Army Map Service after WWII using geodetic surveys of 
>Spain and Portugal performed over the prior 50-75 years! 
> That stuff wasn't that good!
> 
> Try reading my columns on the Grids and Datums of Spain 
>and Portugal at:  www.ASPRS.org/GRIDS  and you'll get a 
>better appreciation of the complexity of the problem 
>being sought with a mere 7-parameter transformation. 
> (Spain is July, 2000, and Portugal is April, 2002)
> 
> Combining Applanix and Trimble gear is cutting-edge 
>geodetic equipment commonly used for Real Time Kinneatic 
>(RTK) Aerial Photography for hair-splitting accuracy. 
> That stuff is working directly in WGS84 Broadcast 
>Ephemeris and is then re-adjusted in post-processed mode 
>with the Precise Ephemeris a couple weeks later.
> 
> That's NOT going to "match" data that's 75-100 years 
>old!
> 
> PROJ4 is a cartographic tool and is not a geodetic 
>panacea.
> 
> Clifford J. Mugnier, C.P., C.M.S.
> LSU Student ASCE Chapter Faculty Advisor
> and
> National Director (2006-2008),
> Photogrammetric Applications Division
> American Society for Photogrammetry and Remote Sensing 
> and 
> Chief of Geodesy,
> CENTER FOR GEOINFORMATICS 
> Department of Civil Engineering 
> CEBA 3223A
> LOUISIANA STATE UNIVERSITY 
> Baton Rouge, LA  70803
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> Honorary Life Member of the 
> Louisiana Society of Professional Surveyors 
> Member Emeritus of the ASPRS 
> Member of the Americas Petroleum Survey Group
> ======================================================
> http://www.asprs.org/resources/GRIDS/ 
><https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=http://www.asprs.org/resources/GRIDS/> 
> ======================================================
> 
> ________________________________
> 
>From: proj-bounces at lists.maptools.org on behalf of Roger 
>Oberholtzer
> Sent: Mon 19-Nov-07 16:24
> To: PROJ.4 and general Projections Discussions
> Subject: Re: [Proj] WGS84 to ED50
> 
> 
> 
> 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
> Ramböll Sverige AB
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> 
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> 

Dean C. Mikkelsen, B.Sc., P.Eng.
Terra ETL Ltd.
Victoria, BC, Canada

Phone/Mobile: +1 (250) 88TERRA (83772)
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