On 7/30/2016 1:57 PM, Andrew Harvey wrote:
On Sat, 30 Jul 2016, at 08:40 AM, Warin wrote:
The change, distance wise, is upto 1.5 metres, well within commercial
GPS uncertainties.
The change is to the datum. How this will work out with future global
datums we will have to wait and see.
In another 30 years there will probably be another change of around 1.5
metres again.
As receivers become more accurate and folks start use other ground based
positioning technology that gives millimetre accuracy, then that data in
OSM will over time become more out of sync as the tectonic plate moves
while the coordinate system remains fixed.
When that happens it would be good to see a future OSM API that lets us
upload data in a coordinate system like GDA so that we don't need to be
constantly updating coordinates to reflect the move in the techtonic
plate.
Sigh.
Simply changing from AGD66 to GDA94 can produce a change of around 100 metres
in location of a coordinate.
So a change in datum can correct the drift without changing the coordinates.
From the above you can see that OZ moves at upto about 50 mm per year.
At present there is no datum system that 'drifts' over time, that would give a
system that would need little alteration and fewer of them.
People who require the accuracy take into account the drift (usually
professional surveyors with very expensive receivers, antennas etc.).
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