[PROJ] MGA94/MGA2020

[Greg Troxel]

Even Rouault <even.rouault at spatialys.com> writes:

> There are known time-dependent transformation between GDA94 and
> ITRF2014 or GDA2020 and ITRF2014. Your GPS probably outputs
> coordinates in WGS 84 (G1762) (or maybe another realization), but you
> may perhaps try to assume that ITRF2014 and that WGS 84 are equivalent
> for your purposes.

Agreed, but even worse:

  If your receiver is not doing differential it will output "WGS84(G1762)
  current epoch".

  If it is doing differential (apparently no SBAS there) it will output
  in the frame of the differential system.  I think US WAAS, not
  relevant in .au, is in IRTF2008, but it's remarkably hard to find that
  out.  

  Each ITRF has a normal reference epoch, and if you are worried about
  the 7 cm/year motion of .au, you may want to pay attention to that.

  If you aren't doing short-baseline differential or RTK, then this may
  not really matter.  If you are, I would not be surprised if your
  coordinates are in GDA2020.  As an example, RTK in the US is typically
  in "NAD83(2011) epoch 2010.0" which is our national
  more-or-less-plate-fixed datum.
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