[Proj] Using Proj.4 to compress a 10-parameter Molodensky-Badekas datum shift into 7 parameters

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In reply to:

[Proj] Using Proj.4 to compress a 10-parameter Molodensky-Badekas datum 
shift into 7 parameters
Noel Zinn (cc) ndzinn at comcast.net
Fri Oct 15 13:57:24 EST 2010

Your provision of a worked example "compressing" a M-B transformation into a
7-parameter transformation is a real contribution.  Thanks ... and thanks to
Melita Kennedy, too.

I've coded this example in Matlab and agree with your final results
> 66d4'54.705"W   9d34'49.001"N   180.499

Nevertheless, I disagree with your first intermediate computation
>  2464278.090  -5783490.207  974643.507

My intermediate results are
=>  2464278.08979296  -5783490.39620226   974642.385933922

etc...

REPLY:

I have no difficulties reproducing the EPSG example exactly with my own 
Molodensky-Badekas routines or with Mikaels procedure around an M-B 
corrected set of dX,dY,dZ for a 7-parameter datum shift.
Please note that M-B parameters are usually stated as for a coordinate frame 
rotation model, whereas PROJ4 uses a position vector rotation model.
One shouldn't always blame PROJ4.
I haven't tested the geocentric -> geodetic code from PROJ4's geocent.c, but 
it certainly looks good.

Oscar van Vlijmen