[PROJ] WGS 84 to GDA2020 in EPSG

[Greg Troxel]

Javier Jimenez Shaw via PROJ <proj at lists.osgeo.org> writes:

> Hi
>
> Preparing a talk for FOSS4G Europe in Tartu (see you there if you come!), I
> found that the 3 transformations  in EPSG from WGS 84 to GDA2020 (2, 3 and
> 4) they all have 3m accuracy.
> That is not giving a clue to PROJ about which one is better.
>
> (2) is a null Helmert transformation.
> (3) is a Helmert with 7 numbers
> (4) uses a grid.
>
> Is there anybody from the Australian agency here? Is there any reason why
> the three transformations have the same accuracy? I would expect different
> values. I looks like a copy-paste issue.
>
> The same happens with the transformation from WGS 84 to GDA94.

Part of the problem is likely "WGS84 is an ensemble" and how proj
handles that.  I'll leave it at that today :-)

Have you looked for transforms from recent realizations of WGS84 (or
ITRF) to GDA2020?  For transforms from the ensemble, 2m (maybe it's 3m
there) is the best you can do.

Sorry  but I think the ensemble issues have to be detangled to really
address this.