[MetaCRS] CS-Map: info about EUROP50-7P,
a 7-parameter ED50-to-WGS84 datum shift?
Mikael.Rittri at carmenta.com
Tue Feb 3 07:47:11 EST 2009
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:
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
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).
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