[PROJ] MGA94/MGA2020

[henning at kaarta.com]

Hello,

I have a set of ground control points provided by a surveyor in Australia
that were created in June 2020.

They are expressed in MGA94 / Zone 56 CRS, which I believe is EPSG:28356.

I would like to convert these points to MGA2020 (EPSG:7856) and relate them
to actual data coming from a Trimble GPS today.

Using PROJ7, I am able to get transformed values between MGA94 and MGA2020
that reflect the displacement of the Australian continent between those
CRSs, e.g. (using some round numbers to illustrate here)

 

echo 300000 6000000 0 | cs2cs +init=epsg:28356 +to +init=epsg:7856 -d 3

300000.435          6000001.421 0.000

 

However, in comparing the results to current readings from the GPS,  I see
they're off by what may be the continental drift that's occurred in the last
15 months - about 8 cm northeast.

I know PROJ7 knows about time-dependent transformations, I just can't seem
to figure out how to use that to get my GCP coordinates in today's MGA2020
grid. I've naively tried

 

echo 300000 6000000 0 2020.5 | cs2cs +init=epsg:28356 +to +init=epsg:7856 -d
3

300000.435          6000001.421 0.000 2020.5

 

but it comes up with the same numbers. 

Do I need to construct a more elaborate pipeline, and is this even something
cs2cs can be used for?
Any tips or tricks would be appreciated! As you might have guessed, I'm
pretty much a novice with PROJ7.

Thanks,

Henning Pangels

 



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