[Proj] Meaning of 7-parameter transformation rotations

Frank Warmerdam warmerdam at pobox.com
Wed Nov 30 14:16:46 EST 2005

On 11/30/05, Clifford J Mugnier <cjmce at lsu.edu> wrote:
> Gentlemen:
> Note that the SENSE of the rotations have two common usages.  The American
> Standard versus the European Standard differ!  To transform in the same
> direction, the signs are OPPOSITE from one "standard" to another.
> Generally speaking, a 7-parameter  transformation, whether it is a
> Bursa-Wolfe or a Molodensky, MUST have a "test point" provided so that the
> user knows which sense the rotations need for the desired transformation
> direction.
> The Americans, Australians, and Luxemborgs use one SENSE, the Europeans use
> the other.  In regard to the rest of the world, it depends on which
> brand-name of GPS Geodetic Processing software was used to derive the
> parameters from some collection of data points.  See my monthly column for
> such important minutiae for country to country considerations.
> Be careful of 'dem signs!  :-)


Your point is quite correct.  I believe that PROJ
is using the European definition so that we can directly
apply the numbers from EPSG.

Test points are always a good idea.  I wish the EPSG
database came with a test point for each coordinate system.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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