@lurker I had to stop thinking of all of the varibles, my head was starting to hurt. Compensating magma movement, China population, tidal redistribution pulling the moon out of orbit, all of my control points no longer accurate. Blam.
I wonder about volcanic eruptions. It could be argued that magma stays earthbound, but there's a heckuva lot of water vapor and gases being thrown out, too. Ash that was concentrated in a small space is redistributed worldwide.
But maybe the solution is to have farmers 180 degrees around the earth from our midwest to draw out an equal amount of water.
Both start from an autonomous postion. It is the same thing, just a longer observation time. 15 minutes of static is the same as 2 hours of static, just longer and more precise. Autonomous positions are just as accurate as a NAD83 position, its just the value that is different.
Where did that original CORS value come from? Of course it is adusted, just like your traverse gets adjusted. The value may change, but it is still just a nail in the dirt measured with the same two angles and same two distances.
The CORS Stations that I use get revised annually from new autonomous postions.
I think we are discussing two different things. I'm not against using autonomous positions, and I don't disagree that autonomous positions will converge over time. (They can, however, bounce around a lot more or a lot less depending on where the receiver is and local conditions.) I was focusing on the implications of selecting one system vs another in the software.
The NGS doesn't typically revise NCN positions on a yearly basis. Usually it's only when a new antenna is installed, or it drifts by several cm. Are you using local/state CORS?
I wonder about volcanic eruptions. It could be argued that magma stays earthbound, but there's a heckuva lot of water vapor and gases being thrown out, too. Ash that was concentrated in a small space is redistributed worldwide.
But maybe the solution is to have farmers 180 degrees around the earth from our midwest to draw out an equal amount of water.
Austrailia could become a rainforest again, all in the name of saving the planet.
Both start from an autonomous postion. It is the same thing, just a longer observation time. 15 minutes of static is the same as 2 hours of static, just longer and more precise. Autonomous positions are just as accurate as a NAD83 position, its just the value that is different.
Where did that original CORS value come from? Of course it is adusted, just like your traverse gets adjusted. The value may change, but it is still just a nail in the dirt measured with the same two angles and same two distances.
The CORS Stations that I use get revised annually from new autonomous postions.
I think we are discussing two different things. I'm not against using autonomous positions, and I don't disagree that autonomous positions will converge over time. (They can, however, bounce around a lot more or a lot less depending on where the receiver is and local conditions.) I was focusing on the implications of selecting one system vs another in the software.
The NGS doesn't typically revise NCN positions on a yearly basis. Usually it's only when a new antenna is installed, or it drifts by several cm. Are you using local/state CORS?
NGS and CORS Station are two differents things on two different ellipses. Go to a CORS Station that you use. In the archives, you can find the value they used last year and the year before. If reprocessing old data, you need to use that years data. I am not trying to be a butt, I do a good job of that without trying, but there is info in this overall post that I dont believe to be accurate, or more exactly, not stated correctly.
FWIW, any visit to Australia should include visits to the Gondwana Rainforests. Lovely, lush, verdant with abundant wildlife.
Wooah, had no idea. See what a little groundwater will do.
I did not realize this was an old post. There are broken links embedded in some replies.
For the Helmert transformation parameters used by the US NGS for NAD83 #### to ITRF #### see: https://geodesy.noaa.gov/CORS/news/historical_helmert.shtml
NGS and CORS Station are two differents things on two different ellipses.
There may be other CORS from sources outside the NGS, but there is a single NOAA CORS Network (NCN).
The NGS does not change the published values for the NCN every year. They spell out pretty clearly under what conditions those values might change.
Go to a CORS Station that you use. In the archives, you can find the value they used last year and the year before.
The nearest NCN CORS to me is SEDR. Its value has been modified three times per its coordinates page link.:
If I pull data for SEDR from three years ago, the .DS datasheet I get has the exact same coordinates as it does today. The RINEX header has the same information.
The short-term and long-term time series shows how the daily solution compares to the published solution, but the published solution is not being modified year-over-year. It explicitly shows their variation with respect to the last adjusted position (MYCS2).
Now, if we are talking OPUS solutions, those positions are computed in ITRF (currently ITRF2014) at the current epoch (technically the middle of the observation) and transformed back to NAD83(2011)[2010.00]. But that's a different application and a different workflow.
As autonomous positioning relies on the broadcast ephemeris, users interested in its accuracy might want to view this article: https://iopscience.iop.org/article/10.1088/1757-899X/631/4/042013/pdf
As autonomous positioning relies on the broadcast ephemeris, users interested in its accuracy might want to view this article: https://iopscience.iop.org/article/10.1088/1757-899X/631/4/042013/pdf
Which is why we dont use a single satellite to obtain a position.
NGS and CORS Station are two differents things on two different ellipses.
There may be other CORS from sources outside the NGS, but there is a single NOAA CORS Network (NCN).
The NGS does not change the published values for the NCN every year. They spell out pretty clearly under what conditions those values might change.
Go to a CORS Station that you use. In the archives, you can find the value they used last year and the year before.
The nearest NCN CORS to me is SEDR. Its value has been modified three times per its coordinates page link.:
If I pull data for SEDR from three years ago, the .DS datasheet I get has the exact same coordinates as it does today. The RINEX header has the same information.
The short-term and long-term time series shows how the daily solution compares to the published solution, but the published solution is not being modified year-over-year. It explicitly shows their variation with respect to the last adjusted position (MYCS2).
Now, if we are talking OPUS solutions, those positions are computed in ITRF (currently ITRF2014) at the current epoch (technically the middle of the observation) and transformed back to NAD83(2011)[2010.00]. But that's a different application and a different workflow.
Yea, them NOAA sites, I dont use them. Checked a couple months ago when I was near one and was only 1.9 feet out. At least they are getting better. The nearest three are 100 miles away. Not a good solution, but knock yourself out.
Evidently you did not carefully read the article. It does not discuss using one SV for positioning. It does, in the context of analyzing the accuracy of broadcast ephemeris data, focus on one SV as an example.
See:
Yea, them NOAA sites, I dont use them. Checked a couple months ago when I was near one and was only 1.9 feet out.
To be clear, are you saying that there are NGS CORS that are both active and 1.9 feet away from their current published position?
I'd be interested in how you managed to occupy a CORS that already has an antenna on it, especially considering many CORS positions are not physical monuments, but the antenna's ARP or L1/L2 position.
concentrated in a small space is redistributed universally
