[MetaCRS] RE: CS-Map: info about EUROP50-7P, a 7-parameter ED50-to-WGS84 datum shift?

[Norm Olsen]

Hello Mike . . .

Yes, you got the correct list.

The definition in question was added to the dictionaries by an employee who is no longer with us, so there is no resource to refer to other than the Portuguese authority or ESRI.  It sure looks like a simple typo by someone.

I did find the following: http://www.asprs.org/resources/grids/04-2002-portugal.pdf

May quick look did not find any 7 parameter definitions, but it did have an promising reference (although it appears to be seven years old):

Thanks go entirely to Jorge Teixeira
Pinto, director of Geodetic Services,
Instituto Portugués de Cartografia e
Cadastro.

At ESRI, the person to contact is Melita Kennedy.  She might be able to provide a degree of confidence that the ESRI definition is correct.

Norm

-----Original Message-----
From: metacrs-bounces at lists.osgeo.org [mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of Mikael Rittri
Sent: Tuesday, February 03, 2009 5:47 AM
To: metacrs at lists.osgeo.org
Subject: [MetaCRS] CS-Map: info about EUROP50-7P, a 7-parameter ED50-to-WGS84 datum shift?

Hello,
sorry if this is the wrong mailing list for my question.

I found the following datum shift for ED50 to WGS84 in CS-Map\Dictionaries\datums.asc:

DT_NAME: EUROP50-7P
        DESC_NM: European 1950, mean Values (7 Parameter Transform)
# aka ED50, ED 50
# Used for Austria, Belgium, Denmark, Finland, France, W. Germany, Gibraltar, Greece
# Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland
        SOURCE: IPCC - Instituto Português de Cartografia e Cadastro
        ELLIPSOID: INTNL
     USE: 7PARAMETER
        DELTA_X: -66.863
        DELTA_Y: -134.888
        DELTA_Z: -111.49
        ROT_X: 0.53
        ROT_Y: 0.14
        ROT_Z: -0.57
        BWSCALE: -3.4

which looked interesting, since I couldn't find it in the EPSG's database.
(The only EPSG shifts for ED50 over such a large area are 3-parameter
 transforms taken from US DMA TR8350.2:
 - "ED50 to WGS 84 (1)" with the same area of use, and accuracy 10 m,
 - "ED50 to WGS 84 (2)", with a smaller area of use, and accuracy 6 m,
 the accuracy here is the one-sigma error.)

But I didn't find the accuracy of the 7-parameter transform in the CS-Map
sources.  So I tried to find the Portuguese original source, without success.

However, I did find a similar transform in ArcGIS, called ED_1950_To_WGS_1984_PT7,
( http://gis.sfsu.edu/helpdesk/arcmap/projections/Map_Projection_Tables.pdf ),
which is identical to the CS-Map version, except that
    dX = -68.863 (not -66.863 as in CS-Map).

So, it seems that either ArcGIS or CS-Map has the wrong value for dX, but I don't
know which one.
   I realize that the result of using the wrong dX is probably less than the method
accuracy, but I would still like to know which one is correct.
   More important, I would really like to know the method accuracy (preferably
both the one-sigma error and the maximal error, if the original source gives them).

Best regards,
--
Mikael Rittri
Carmenta AB
SWEDEN
www.carmenta.com
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