Datums and movement

New to surveying and trying to understand datums.

I have a plan surveyed in Oct,94 in GDA94. So I can set the project to match. But, since the survey is so old, does the GPS automatically compensate for the movement in the earth relative to the satellites based on today’s date.

I.e. I’ve just discovered that Australia is moving north east 7cm/ year. But the satellites are not…
2023-1994 = 29. 29yrs X 7cm/yr = 203cm.

A peg surveyed that many years ago is now 203cm away. How is this dealt with?

Thanks in advance

Hi Tristan,

Oh, that’s a good question!

Datums are tied to some surface area (local or global). When that area moves, the datum moves with it. This means that to match your new data to the old project, you need to work in the same datum as before—GDA94.

To collect the data in GDA94 with Reach RS2, you just need to have a base placed in GDA94. If you work with the NTRIP service, check the datum info of the mount points with the provider. If you place the base manually, enter its coordinates in GDA94 in the Base settings tab.

P.S. Just thought to share this page with you. I was curious to read there about the datums in Australia. You might find it useful too.


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