"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, especially for L1-only receivers. Actual data with and without, compared to surveyed reference coordinates, would be interesting. >> >> 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)). > 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. > 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". No, because the plate has moved relative to ITRF2020. and the real point is likely to evaluate changes in coordinates due to measurement accuracy or local motion and one wants to take out plate motion. This is why people use datums like NAD83 in the US, or ETRF in EU, which more or less remove plate motion. When you compare coordinates from different epochs, the difference is the sum of plate motion and the true difference. 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.
