"Gary E. Miller" <[email protected]> writes:
> I do. And it does help. And some u-blox survey grade receivers do not
> even give you the option to use SBAS.
"survey grade" more or less means "carrier phase measurements, post
processed or RTK", which does not care about the navigation solution.
>> especially for L1-only receivers. Actual data with and without,
>> compared to surveyed reference coordinates, would be interesting.
>
> I have done some quick eyeball tests, and confirmed SBAS does not help.
You mean:
autonomous navigation solution, say an hour's worth
vs
navigation solution with SBAS, same time interval
and the averaged position from SBAS is *closer to the true position of
the monument*?
>> Yes, but the data you get back can be in varying datums, including
>> NAD83(CSRS) (which is close to NAD83(2011)).
>
> Not large enough to get the variations Hans is seeing.
NAD83 vs ITRF is big. But he's all ITRFyyyy/WGS84(Gwww) sort of things.
>> Yes, because you are asking "how have the ITRF2020 coordinates changed
>> between a measurement 3 years ago and a measurement yesterday, when
>> those coordinates are expressed as "epoch of data".
>
> That is not large enough to make what he sees. Easy to check. My
> nearby CORS station has charts of historical drift.
True it's not really big enough, but it's unsound to ignore it.
>> Formally, I see it as confused to compare data in a dynamic datum at
>> different epochs, unless you are trying to calculate station
>> velocities. The ITRF papers talk about bringing data to a common
>> epoch in explaining how the ITRF solutions are done.
>
> That makes sense. They keep moving the 0,0,0 point of ECEF. But
> not much more than 10 cm.
The difference in origin/scale/orientiation between recent realizations
is a cm or so.
But the ITRF2020 position of a disk in bedrock in Europe at epoch 2020.0
and epoch 2025.9 is going to be different because the plate is moving
with respect to ITRF2020. Glancing hastily at plate motion data
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GL106373
I am going to assume 3 cm/y for EURA, matching NOAM.
In 6 years, that's 18 cm. That is easily detectable with RTK and a
high-quality RTN.
Even if I'm off by a factor of 2 in rate, it's still detectable.
