[Proj] Re: Campo Inchauspe to WGS84 parameters

Clifford J Mugnier cjmce at lsu.edu
Fri Nov 11 11:44:31 EST 2005

ALL datum shifts are approximations, particularly those that only use the 3
translations.  Accuracy increases as the number of parameters increase
and/or the size of the region being transformed decreases.

One generalization that is ALWAYS correct is that EVERY datum shift will
decrease the accuracy of the original data once it is transformed to the
other datum.

EPSG-published parameters are directed to regions that are predominately
hydrocarbon-producing ... e.g. coastal Argentina.  NIMA-published
parameters are directed to regions that are potential battle zones on land
... e.g. interior AND coastal Argentina.  None of them are "exact."
Classical datums have systematic errors that change greatly over vast
regions.  Argentina is not a small country.  Consider also the many sets of
3-parameter transformations available for the Continental U.S.

For those that "cherry pick" parameters from my columns, I suggest reading
the entire column with the associated background information for the
country of interest.  The primary living authority on Argentine Geodesy is
Mr. Ruben Rodriguez, as referenced in my column.  He is a practicing
Geodesist that lives in Argentina.

Datum shifts are "starters" for general reconaissance.  When one wants the
EXACT transformation parameters for a specific area, one puts a Geodesist
on the ground to find out.  Practical surveying beats out office theory
every time.

Cliff Mugnier

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