Do you mind calling me, and helping me a bit with a couple of GPS Elevation Questions?
In the morning...
870-356-3797
I have an OPUS answer, but it does not jive with some local datum, by a large amount.
Something is not quite right.
Thanks,
Nate
Just curious but what do you use for equipment, L1 or L1/L2? Which brand? I'm asking as I may have a lot of topo to do on a project and I was thinking of gps.
Well, I could not sleep, so I am back on...
I have Topcon /// Javad they are the old Legacy E System, with 4 megs of memory.
I have some files that I have downloaded, and .... they are in TT (Topcon Tools) but I cannot seem to find the actual file... to send to opus. I already deleted the files in the GPS, so I could do more field work, and they show up in TT but the actual file to send to opus is eluding me.
Also, I am getting a note that says that
"ORTHO HGT: [Geoid Model Not Yet Available w/ NAD83 (2011).]"
This does not make much sense to me, because the integration process can be done, but where data is sparse, it's accuracy is just not very good. It seems that they would publish an ortho, and a warning as to it's estimated accuracy.
o well.
N
Nate, select The NAD CORS96 datum, on the right and it will give you an elevation.
> I have some files that I have downloaded, and .... they are in TT (Topcon Tools) but >I cannot seem to find the actual file... to send to opus.
I use a HiperLite, I get a .tps file to send off to OPUS.
I use PC-CDU to get that file.
:dog:
First a clarification...NAD_83(CORS96) and NAD_83(2011) are DIFFERENT REALIZATIONS of the SAME Datum (NAD_83).
As for the GEOID issue with NAD_83(2011), here's my take on it:
The reason that GEOID09 is NOT used with NAD_83(2011) is PRIMARILY due to the adoption of Absolute Antenna Models in both ITRF2005 (IGS05), and ITRF2008 (IGS08), as opposed to the Relative Antenna Models used with ITRF2000 (IGS00) which was referenced by NAD_83(CORS96).
I also suspect that this Antenna Calibration change is [at least in PART) the reason for the NGS' reprocessing of the Passive Network. Basically, ALL of the GPS-on-Bench Mark data used in the Hybrid Geoid Models (eg. GEOID99, 03, 09) was BASED on the RELATIVE Antenna Models, whereas IGS08 (and therefore NAD_83[2011]) is NOT!
From what I have read, GEOID12 will be based on the Absolute Antenna Models as applied to the Passive Network (and hence the GPS-on-Bench Mark Stations), so when GEOID12 hits the street next Spring (March/April?), then we will see Orthometric Heights in OPUS reports again.
Basically, the change to Absolute Antenna Models on BOTH the Terrestrial Antennas as well as the Space Vehicles in IGS08, WILL change the NAD_83 ellipsoid heights somewhat, and we are also talking about eight (8) years of crustal movement that IS more accurately known in the Active (CORS) Network due to the Multiyear Adjustment (but not in the Passive Network).
I hope that made sense (and is reasonably correct too).
Loyal
If the absolute phase center moves about the ARP a little, how can you quantify it? Also, if the L1 and L2 phase centers have different values, which value would be used by OPUS calculations? We will reel in that 0.04 yet!
Loyal
Thank you for your detailed response. I understood a good bit of it.
It seems that I am ever learning.
Folks like you make that process alot easier.
Nate
Loyal
It’s really amazing how GPS works. The people that have put the system together have come up with elegant solutions to very complicated math to obtain the accuracy we are accustomed to. The Earth-Moon system (the Earth and Moon actually orbit each other) is complicated enough, but the GPS system also has to account for gravitational forces of Jupiter, the Sun, the lumpiness of the Earth itself, special and general relativity and how that effects the clocks on the satellites compared to clocks on the surface and although I’ve never heard it discussed, there are ground based tracking sites at different latitudes moving at quite different speeds while rotating around the Earth which must also cause some relativistic distortions. There are tidal forces not just of the ocean but also of the crust and plate shifts.
All this and more is taken into account by the wizards running this system.
Yet, where is so much time and effort spent: Antenna models!
And I’m not being critical, it just seems odd that so much error and confusion in the GPS system revolves around the Antennas. But, that's where we are and everyone using the system correctly needs to be very careful with how they measure their antennas.
😉