[Proj] Using Proj.4 to compress a 10-parameter Molodensky-Badekas datum shift into 7 parameters
ovv at hetnet.nl
Sat Oct 16 07:56:05 EST 2010
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
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
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