[Proj] Amersfoort / RD New

[Bas Couwenberg]

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.

> On Tue, Nov 1, 2016 at 3:28 PM, Bas Couwenberg <sebastic at xs4all.nl> 
> wrote:
> 
>> On 2016-11-01 15:05, Roger Oberholtzer wrote:
>> > I downloaded the grid shift file from
>> > http://www.kadaster.nl/transformatie-van-coordinaten
>> >
>> > I am not using it yet. I took one of the sample points from the Use doc
>> > that came with it to see what I got compared to the expected. For
>> > example:
>> >
>> > Zuid-Limburg:
>> > Ref:   Latitude: 50.7925849160 Longitude: 5.7737955480 Altitude:
>> > 245.948
>> > Ref:   Easting:     182260.450 Northing:    311480.670 Altitude:
>> > 200.000
>> > Proj4: Easting:     182225.909 Northing:    311388.163 Altitude:
>> > 245.948
>> > 98.746 meters from Ref
>> >
>> > The reference values are ETRS89. But I cannot think that accounts to
>> > 100
>> > meters of difference. My proj spec is:
>> >
>> >      +proj=sterea
>> >      +lat_0=52.15616055555555
>> >      +lon_0=5.38763888888889
>> >      +k=0.9999079
>> >      +x_0=155000
>> >      +y_0=463000
>> >      +ellps=bessel
>> >
>> > +towgs84=565.4174,50.3319,465.5542,-0.398957388243134,0.
>> 343987817378283,-1.87740163998045,4.0725
>> >      +units=m
>> >      +no_defs
>> >
>> > Doing this via the C API as I do for many other projections. These are
>> > passed to pj_init_plus.
>> >
>> > Would the grid shift make such a large correction?
>> 
>>  From the proj-rdnap test script (using PROJ.4 4.9.3):
>> 
>>   Test:   05 Zuid-Limburg
>>   Exec:   cs2cs -r +init=epsg:4258 +to +init=rdnap:rdnap -f %.4f
>>   Input:  50.792584908 5.773795547 174.9478
>>   Output: 182260.4500     311480.6701 129.0000
>>   Expect: 182260.4500     311480.6700 129.000
>>   Test OK: From ETRS89 to RD/NAP - 05 Zuid-Limburg (Not identical, but
>> within margin)
>> 
>> The above uses the test values from "Use of RDTRANS2008 and
>> NAPTRANS2008.pdf" included in the NTv2.zip, your values are different,
>> not sure where you got those.
>> 
>> The rdnap configuration for the above test contains:
>> 
>>   # 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
>> <>
>> 
>> Try using the grid shift files for your test, it should be more 
>> accurate
>> (at ground level) than using +towgs84 values.
>> 
>> Kind Regards,
>> 
>> Bas