[Proj] +towgs84 approximation error

Jochem jochem.lesparre at kadaster.nl
Thu Mar 23 04:21:12 EST 2017

Hi Kristian,

I can not show that cs2cs makes an approximation error by using only cs2cs.
I have to compare it with other software. But what transformation software
is available to you that would you trust more than Proj.4? The best way to
show it, is to compute a transformation in computational software like
Matlab twice. One time with the approximate formulas, giving the same result
as cs2cs, and one time with the strict formulas, giving a 4 cm different
result. As not everyone here will have Matlab, I am thinking of using Excel.
Do you think that is a good idea?

Thanks for the information on how to use a development version of PROJ.4
with QGIS. This sounds complicated. Maybe I would manage to do it with a lot
of effort and some help. But I am afraid I can't expect the government
agency here to reproduce that.

In the Netherlands, the official transformation RDNAPTRANS will probably be
updated this year in a way that it can be done with Proj.4. I hoped to be
able to do the same here, but the approximation error is preventing me from
doing so.

Regards, Jochem

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