You tell the DC what to do, not the other way around.
So, you tell the DC that you want, say, an NAD83(2007) autonomous position and it gives you that?
Pretty cool and makes perfect sense.
Thanks.
It gives you a GIS accurate datum if that. No need to worry about what flavor of NAD83 you are in if you are autonomous.
That's been my experience with GIS. When 2022 parameters for NC were published, I took the WKT string from an Iowa LDP and substituted the NC parameters for the Iowa ones that were labeled NAD83(2011).
My old version of Proj.4 searched to see if it had an existing duplcate file. It did, the original NAD83, so it used that with my substituted 2022 parameters.
I didn't specify a name, like 2022 or something, so everything came bace as NAD83.
But, because I entered Lat/Lon, and the ellipsoid hasn't changed, everything was on the money.
So, I filed away in my own "best practices" mind slot: Always convert old SPC data to the same flavor if you're entering plane coordinates. Know that if you enter Lat/Lon, the SPC coordinates are going to be the specific point on the plane that corresponds to that Lat/Lon on the ellipsoid.
GISers really have to think if they're going to get it right.
So, you tell the DC that you want, say, an NAD83(2007) autonomous position and it gives you that?
Pretty cool and makes perfect sense.
Thanks.
No Math Teacher, not what you want. You have to "get it on" what you want. Any autonomous position is irrelevant to the realization or datum.
So, you tell the DC that you want, say, an NAD83(2007) autonomous position and it gives you that?
Pretty cool and makes perfect sense.
Thanks.
No Math Teacher, not what you want. You have to "get it on" what you want. Any autonomous position is irrelevant to the realization or datum.
Autonomous positions are points on the earth with geocentric coordinates and elliptical heights. They are not relative to any station, derivative or correction. They can be reduced to lat long, grid projection or any calculated datum.
OK, help me better understand. If I drive a nail in pavement and set GNSS over it, it's going to record a Lat/Lon position. From that Lat/Lon position, it can calculate SP coordinates. Regardless of 2011, 2007, HARN or whatever, the same SP coordinates will be calculated because there's only one conversion from GRS80 Lat/Lon to SPC.
Now, how do I get it on 2007?
OK, help me better understand. If I drive a nail in pavement and set GNSS over it, it's going to record a Lat/Lon position. From that Lat/Lon position, it can calculate SP coordinates. Regardless of 2011, 2007, HARN or whatever, the same SP coordinates will be calculated because there's only one conversion from GRS80 Lat/Lon to SPC.
Now, how do I get it on 2007?
Your receiver is going to record an ephemeris and several ‘vectors’ from each satellite. It will then calculate an earth based X Y Z coordinate from the ‘vectors’ and known orbits. This X Y Z coordinate can then be adjusted, derived, corrected and translated into any set of values you wish.
earth based X Y Z coordinate
That is in ITRF or WGS84. All the other expressions are conversions done in your hardware/software. An autonomous position is typically accurate to the meter level. If you process your data against data from the same time at a "known" station such as a CORS, then you can get centimeter accuracy relative to that known position.
earth based X Y Z coordinate
That is in ITRF or WGS84. All the other expressions are conversions done in your hardware/software. An autonomous position is typically accurate to the meter level. If you process your data against data from the same time at a "known" station such as a CORS, then you can get centimeter accuracy relative to that known position.
Correct, but maybe I believe the earth is the center of the universe.
OK, help me better understand. If I drive a nail in pavement and set GNSS over it, it's going to record a Lat/Lon position. From that Lat/Lon position, it can calculate SP coordinates. Regardless of 2011, 2007, HARN or whatever, the same SP coordinates will be calculated because there's only one conversion from GRS80 Lat/Lon to SPC.
Now, how do I get it on 2007?
Your receiver is going to record an ephemeris and several ‘vectors’ from each satellite. It will then calculate an earth based X Y Z coordinate from the ‘vectors’ and known orbits. This X Y Z coordinate can then be adjusted, derived, corrected and translated into any set of values you wish.
Perhaps most importantly, the raw ECEF XYZ values being recorded are referenced to the ITRF, on the current realization, at the current epoch of measurement. So if I were to record data today, my raw measurements would natively be in ITRF2020 at epoch ~2023.485 (julian day 177 out of 365).
If I don't want those values, I have to tell my data collector or my post-processing software where the receiver actually is.
If I feed my base NAD83(2011)[2010.00] coordinates, it's going to continually make the correction from the autonomous position (which is continuously bouncing around) to those values, and broadcast that difference to the rover, and subsequently to the DC, where that ECEF vector is transformed to a LLH at the rover and then to a projected grid coordinate (and sometimes transformed further to a ground coordinate or maybe a custom transformation).
If I instead choose to feed my base HARN values, my rover will be working in HARN.
I can do the same thing in my post-processing software - tell it that my receiver was actually over here, and not over there. The ECEF vector computations are simply translated with respect to the base location, and the reductions to geodetic are simple as both ITRF and NAD83 use the GRS80 ellipsoid (ok, technically the ITRF does not use any ellipsoid, but that's the recommended and industry standard model).
OK, so you define the coordinates of a specific point in your preferred datum and the software calculates coordinates relative to that specific point. Then everything is on your preferred datum.
Is that right?
OK, so let's replace the nail in pavement with NGS mark EX4026. If I set the GNSS over that mark, I want it to give me the superseded coordinates below:
EZ4026 NAD 83(2007)- 35 59 49.32944(N) 079 54 47.97618(W) AD(2002.00) 0How do I do that?
Firmware and Software. Every unit is different. I pretty much have to hook my unit up to a desktop or cell phone to change stuff that deep. I am afraid I might not switch it back. There are hundreds of formats and dozens of coordinate systems, It makes my head spin. Right or wrong, I just use Rinex for static, assumed grid for BaseRover, SPC for rtkN and ground for robot. I can look at any raw file and know where it came from.
It's not easy, is it? That's why I admire you guys, what you know, and the work that you do.
Thanks for the help.
