[Proj] Amersfoort / RD New

[Roger Oberholtzer]

On Wed, Nov 2, 2016 at 9:48 AM, Bas Couwenberg <sebastic at xs4all.nl> wrote:

> On 2016-11-02 09:36, Roger Oberholtzer wrote:
> > I have updated to 4.9.3. My rdnap file is identical to yours:
> >
> > # RDNAP with NTv2 and VDatum
> > <rdnap> +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889
> > +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel
> > +nadgrids=rdtrans2008.gsb +geoidgrids=naptrans2008.gtx +units=m
> > +no_defs
> > <>
> >
> > If I run this:
> > cs2cs  -r +init=epsg:4258 +to +init=rdnap:rdnap -f %.4f
> >
> > And provide these locations:
> >
> > 50.792584908 5.773795547 174.9478
> >
> > I get this:
> >
> > 182225.9086     311388.1617 128.9976
> >
> > Not the values you listed:
> >
> > 182260.4500     311480.6701 129.0000
> >
> >
> > I'm confused.
>
> Does your epsg file use +towgs84 values for EPSG:4258?
>
>   # ETRS89
>   <4258> +proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs  <>
>
> I guess you're on Windows, which uses a different libc that may also
> explain the divergence.
>

I'm on Linux. I see that when I updated my libproj, a new epsg file was
installed. I don't usually use that file. I did here because I wanted to
duplicate your exact command. 4258 is defined as:

<4258> +proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs  <>

I'm curious why you use both the definition in the epsg file, as well as
the one in rdnap. Why not everything in the rdnap file? What is your
definition for 4258?

If I change my command to:

cs2cs  -r  +to +init=rdnap:rdnap

I see that the grid shift file is now read. But my computed values are
still:

182225.9086     311388.1617 128.9976




-- 
Roger Oberholtzer
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