Re: my total miserable failed experiment with PPP and rtklib

[Greg Troxel]

Hans Mayer <gpsd@ma.yer.at> writes:

> On 25.07.23 01:01, Greg Troxel wrote:
>> rtlklib itself has a comlicated history, and you should be aware of
>> rtklibexplorer, and likely use their code.

My point is that rtklibexplorer's version of rtklib is at least
semi-recently maintained, and has fixed a lot of things.

>> Missing from your discussion was a mention of datum.   GPS itself will
>> give positions in WGS84(G2139) at least this week.  But as soon as you
>> use SBAS you get positions in the SBAS reference frame.  If you are in
>> .at, vs just using a .at email address, that is likly EGNOS and thus
>> probably some ITRF2008 or ITRF2014 -- but do look it up and tell us.
>
> This I have to verify. But SBAS was switched on.

So if being pedantic, which you should be, you have to look up EGNOS
docs and figure out their reference frame.  But all modern WGS84 and all
modern ITRF are basically the same, at the cm level.

> Are there recommended online tools to recalculate from WGS84 date ?

This question doesn't make sense to me.

>> Then, for a reference station, questions arise:
>>
>>    how stable is the antenna mounting?
>
> Fix mounted on the top of the roof.  But a tornado could break it :-(
>
>>    is it a geodetic-grade antenna
>
> no idea.

I didn't mean your station.  I meant the reference station whose data is
being sent to you via NTRIP.

> As antenna I use the recommended multi-band active gnss antenna
> HAB-ANN-MB-00-00 with SMA Connector from ublox.…
>
>>    is it dual frequency?
>
> Yes.

As Gary said, this is not a great antenna.   It's a workable antenna for
mobile use.  Look at eg the TOP106 from sparkfun, and similar units from
ardsimple.

>>    how was the reference position determined? *
>>
>>    what datum is the reference position in? **
>>
>> * There is a dreadful culture of using several minutes of "survey in" to
>>    establish position.   That can be ok for some uses, if understood, but
>>    it is not ok for a public NTRIP feed.
>
> I used this ntrip streams
>
> https://igs.bkg.bund.de/ntrip/streams
>
> it seems that this base stations are running since a while.

So you have to dig in and read the metadata about the particular stream
you are using.  I am using MaCORS, a service of the Massachusetts
Department of Transportation (MassDOT), which is using Leica equipment
set up to professional surveying standards.  It is documented to be in
NAD83(2011) epoch 2010.0 and they base coordinates on static solutions
relative to NGS CORS (which is the foundation of active control in the
US).

If the reference station you are using -- not just the NTRIP service --
is not run by someone who is at the level of a professional surveyor
(they can be an amateur; they just need to be that
careful/knowledgeable) then you cannot really trust it.