Yo Greg! On Sat, 20 Dec 2025 20:48:24 -0500 Greg Troxel <[email protected]> wrote:
> "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. I think you over sepcify. All I meant was not the cheap stuff. > >> 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 Yes. > and the averaged position from SBAS is *closer to the true position of > the monument*? No, further. SBAS degrades the fix quality. THis is obvious with gpsprof. > >> 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. But when talking "accuracy" we are using consistent datums. > >> 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. And yet, 99% do. > > >> 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. Depending on your definition of "recent". > 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. Seems about right. > In 6 years, that's 18 cm. That is easily detectable with RTK and a > high-quality RTN. And much smaler than Hans is seeing. So not a complete explanation of his errors. And then only if he is using the wrong datum. > Even if I'm off by a factor of 2 in rate, it's still detectable. Of course. We know, because we see it. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 [email protected] Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can't measure it, you can't improve it." - Lord Kelvin
pgpehczixxeSh.pgp
Description: OpenPGP digital signature
