[PROJ] Static/Dynamic Webmapping Problem version 2.0

[Even Rouault]

> So if you start out in 1994 and keep measuring the same point in GDA94, its
> coordinates will change and get increasingly far from their initial value.

When you say "same point", you mean a point at fixed coordinates in ITRF right 
? (so contrary to common langage where when talking about "same point" we 
generally think of a point physically attached to the plate (not talking about 
region subject to crustal deformation/earthquakes)).

> In GDA2020 they will also change with time, but instead will approach the
> GDA94 numbers measured in 1994, until in 2020 they will be the same--but
> then start diverging again. The point is that the coordinate values
> measured at a place in 1994, expressed in GDA94, will match the values
> measured at the same place in 2020 expressed in GDA2020. Neither is
> plate-fixed. 

> There will be a time-dependent reference frame known as the
> Australian Terrestrial Reference Frame (ATRF) that is plate-fixed: in 2020
> it will match GDA2020.

Hum, my understanding of ATRF (based on 
http://spatialservices.finance.nsw.gov.au/__data/assets/pdf_file/
0018/217224/2017_Janssen_Position90_GDA2020_AUSGeoid2020_and_ATRF_explained.pdf 
) is that it is NOT plate-fixed. It is a realization of ITRF, so it is as 
Earth-fixed as ITRF is. Basically coordinates in ATRF at yyyy.yy should be pretty 
much the same as if expressed in WGS84(G1762)@yyyy.yy

Even

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