Yo Greg! On Sat, 20 Dec 2025 19:20:47 -0500 Greg Troxel <[email protected]> wrote:
> "Gary E. Miller" <[email protected]> writes: > > > Most people doig high preceicion just turn off the SBAS stuff. It > > is lower wuality than the basic GPS now. > > I hear people say that. It's not clear to me that it's true, I do. And it does help. And some u-blox survey grade receivers do not even give you the option to use SBAS. > 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. And, as you imply, if you have L2, you don't need the ionosphere corrections from SBAS. All the GNSS signals are publicly available, except the SBAS ones, so hard to say exactly what is in the SBAS signals. > > >> >> After that, if you are using a dynamic datum (Egnos TRF, ITRFnn, > >> >> WGS84), or a static datum on the wrong plate (NAD83 in EU), then > >> >> you need to bring positions to a common epoch to compare them. > >> >> > > > > This does not really apply with CSRS-PPP. All you send to them is > > your measured psuedoranges. Before any corrections have been done > > in the reciver. > > 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. > > The CSRS-PPP uses the currenent IRTF, or the IRTF of the time an > > older statsset was acrquired. > > This is blurring two things. Every 5ish years, there is a new ITRF > reference frame. And then, for e.g. ITRF2020, the coordinates have > some epoch. There is a default epoch for data that does not have an > epoch label. Not large enough to get the variations Hans is seeing. > > Then Hans is just comparing the results from CSR-PPP for data taken > > at different times. So, Apples to Apples. > > 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. > When you compare coordinates from different epochs, the difference is > the sum of plate motion and the true difference. Yes, which is not the 2 meters Hans is seeing. > 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. 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
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