[PROJ] Could you please explain me why I can't project RDN2008 (EPSG:6706) to ERTF2000 (EPSG:9067) or ITRF2000 (EPGS:8997)

[Greg Troxel]

Giacomo Cappellini <giacomo.cappellini.87 at gmail.com> writes:

> Just side note: I'm actually quite surprised about your question about
> WGS84 "Are such non-null transforms between members published somewhere ?"
> as I was considered that like an obvious fact. If this information is not
> officially available to the public, what's the whole point of updating the
> datum? Considering that WGS is currently aligned with ITRF2014 at 2010.000, is
> this made to push new maps to ITRS (that provides all the numbers)?

The new realizations are solutions are estimates of station coordinates,
for the stations in the GPS tracking network.  Because of the way those
are done, they end up being very close to some ITRF (which is quite
intentional).  These are then used to monitor signals and thus the
broadcast orbits are in this frame.  This is useful all by itself --
positions computed by users are more closely aligned to ITRF with every
succeeding WGS84 realization.  This does not require publishing or even
computing a transform from the previous version.

Often, NGA has published transforms, or other people have from analyzing
the changes in station coordinates.  It's important to realize that much
of the new realization is reducing errors and little of it is systematic
shifts, for recent realizations.

Veering off topic for the list, but it's important to understand that
only GPS-only, non-differential (so no SBAS in use!) solutions are in
the WGS84(Gwwww) frames.  Once you use SBAS, the solution is in the
frame of the SBAS reference stations.  I think that's ~always some
recent ITRFyyyy, or an analogous IGSyyyy related frame, but it's
remarkably difficult to get a precise, documented answer.  That's
probably because unless you are doing precise geodetic surveying, all
recent WGS84 and all recent ITRF are equivalent.  And if you are, you're
doing day or multiday static double-differenced carrier phase solutions,
which avoid the "what frame is GPS in' entirely.

I have not been able to find reference frame information published for
the US WAAS, for example.

EGNOS is similarly difficult to find information about.  I was able to
find a paper from 2007 that says that it then used ITRF2000:
  http://geodesy.unr.edu/hanspeterplag/publications/pubs/2007_plag_etal_egnos.pdf

Practically, the errors from autonomous solutions and SBAS solutions are
so vastly greater than the frame differences that I doubt anyone could
tell the difference, even with a year of averaging.  Contrary facts
welcome of course :-)
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