[Proj] +towgs84 approximation error

[Kristian Evers]

Jochem,

> I can not show that cs2cs makes an approximation error by using only cs2cs.
> I have to compare it with other software.

Sure you can.

You have coordinates that you trust and know to be true, right? Let us
see those. Both the coordinates before and after the transformation.
Then do the transformation with cs2cs. Use the same parameters as
the trusted coordinates were created with. Now we can compare the
two sets of coordinates, and maybe figure out what is going on here.

Kristian



> -----Oprindelig meddelelse-----
> Fra: proj-bounces at lists.maptools.org [mailto:proj-
> bounces at lists.maptools.org] På vegne af Jochem
> Sendt: 23. marts 2017 10:21
> Til: proj at lists.maptools.org
> Emne: Re: [Proj] +towgs84 approximation error
> 
> 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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> tp5313738p5313821.html
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