NGS Technical Report 62 on geometric coordinates released

Wow, looks very interesting.

It will take a little time to digest this baby.

Thanks Mike
Loyal

Thanks, this is a good paper on just how complicated it is to keep the CORS system up, running and updated.......

Loyal, post: 433660, member: 228 wrote: It will take a little time to digest this baby.

No kidding. But in a quick look, I was interested to note that they're down to a level below tectonic plate motion, where they can plot distortions in the plate as well.

That's interesting for sure. I feel like I'm pretty savvy as a surveyor who uses geodesy while not being a geodesist. I understand the approach to the Euler rotation, if not all of the math discussed in the paper, but I don't know that I have a good grasp on what the end product will be for me to build my surveys on (mapping, as the paper refers to it). I think it will be counter-productive. If a surveyor can't understand what he's getting or how to use it, he's not going to use it. I think they over-thought it for us "mappers". Maybe implementation will be simpler than what I imagine though...

I certainly haven't digested it all, but what I've absorbed so far looks like minimal change in methods from what we're used to. Am I wrong?

Currently, OPUS or your proprietary tools find a position in IGS coordinates at current epoch and transform to fixed-epoch, plate-fixed NAD83(2011). Won't the new implementation essentially do the same steps with new tables/formulas to get 2022 coordinates? Those will be plate-fixed within similar accuracy to what we're used to? Then they have identified additional time-dependent regional corrections that may get to even better accuracy.

From what I read, the OPUS result will be time dependent and then there will be the IFV (intra-frame velocity) version which sounds similar to HTDP for local velocities, but I still don't know if it will be to a specific epoch or not. I didn't quite catch what they were saying there. You may be right.

Re-reading some of it gives me the impression that OPUS will apply the major time-dependent transformation due to Euler pole motion, and only that transformation. We can probably use that result like we use NAD83(2011), except of course it is calculated for the 2022 definition. There won't be frequent changes of datum tag like we've had with NAD83(86) (HARN) (2007) (2011), but it says at the top of p. 19 they might need to update the Euler pole data every decade.

There is a difference in philosophy, p. 20: "The goal of applying the Euler Pole rotation ... is not to arrive at 2022 coordinates at a reference epoch, but to arrive in that [frame] at the same epoch as the IGS frame." I think if Intra-Frame Velocity were zero, this distinction would be moot.

Page 18: "The intra-frame velocities will not be removed when NGS provides coordinates ... Instead they will be provided as a separate service by NGS ..."

Page 19 indicates to me the Intra-Frame-Velocity tool will be somewhat analogous to HTDP to get estimates of where a point was at a given epoch of your choice. However, they aren't claiming geodetic accuracy for this tool, only an accuracy that may be useful to users. The IFV may have a version tag; p. 29 indicates that as NGS accumulates data in the future they may update it every 5 to 10 years.

It isn't clear to me how important the latter will be for various surveying applications. I happen to be in about the most stable place shown in their figure, with a tiny IFV. But I can see New Englanders and folks in several other areas needing the IFV calculation for a lot of careful work, more so as time goes on and the differences accumulate. The west coast may need IFV corrections for most survey work, which won't surprise anyone out there.