GNSS/WAAS User from Georgia

I'm not sure I understand what you're asking, but it sounds like you are looking for a way to assess true accuracy.?ÿ Explore the National Geodetic Survey's NGS Data Explorer (geodesy.noaa.gov/NGSDataExplorer/) and find a benchmark with GPS and vertical control (solid black circle with solid black triangle).?ÿ Looking at the sparsity of them in Georgia makes me appreciate North Carolina.

Take your mapping grade unit and locate the NGS benchmark and see how it compares to the published coordinates. The benchmark data sheets can be a bit overwhelming but I believe there are help guides on NGS's website. If not, just post it here and I or someone else can walk you through it.

You might want to check out Bad Elf Flex?ÿ or Extreme.

Another option would be to get together with a surveyor and establish your own benchmark near your work area.?ÿ Regardless of the unit, mapping or survey grade, it's a good idea to tie into a known point or two to reduce the risk of a blunder.

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Well, I'm not altogether sure all that you are involved in, however, the only way that I know of to be 100% sure of gnss data is some form of redundancy.

We can essentially remove from our equation full autonomous shots, as they don't have the underlying data to achieve the accuracy needed.

This brings us to DGPS. Differential GPS. Which is what we use.?ÿ

With DGPS, we need some sort of redundancy. For that we usually use time.

In canopy situations, you can use lots of time.?ÿ

Anyway, I'm curious, as to your full motivation, and specifications needed.?ÿ

Lots of USED gps gear is available, that can probably meet your specs, on a budget.

Talk more, and others can point you in a good direction.

Nate

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At the accuracy expected of a unit relying on WAAS you probably don't need to worry about which ITRF version.

If you compare to an NGS data sheet, it is essential to understand the difference between ITRF and NAD83(date), which may be a couple meters.

I don't know how your receiver treats datum conversions, but I would be suspicious of taking it at face value, and want to do that comparison. Some major manufacturers labeling is confusing (Trimble has been discussed in that regard). I know older Garmin sports receivers ignored the difference between WGS84, which is a snapshot of ITRF, and NAD83 which is tied to the moving North American tectonic plate.

The NGS site has conversion tools that will be useful.

I have done testing on well surveyed points (?ñ0.01 m with respect to ITRF) with survey grade receivers/antennas. As Bill stated, the accuracy of WAAS renders the question of which ITRF version moot.?ÿ

I have a Trimble alloy running at the office, it usually has RTX turned on. I just now switched off RTX and turned on SBAS corrections (WAAS). Here is a plot showing the jump when RTX was turned off. The RTX is usually within ?ñ1 or 2 cm.?ÿ

Here is the vertical...

I also turned on a GGA NMEA output at 1 hz, and and capturing the data stream. I will post later today or tomorrow morning a plot of the WAAS positions.?ÿ

I should add that the reference position is NAD83 (2011) epoch 2010.0, transformed from ITRF2014 using HTDP including 60 days of data. This is because I use it as an internet base for RTK over cell.?ÿ

I have done testing on well surveyed points (?ñ0.01 m with respect to ITRF) with survey grade receivers/antennas. As Bill stated, the accuracy of WAAS renders the question of which ITRF version moot.?ÿ

I have a Trimble alloy running at the office, it usually has RTX turned on. I just now switched off RTX and turned on SBAS corrections (WAAS). Here is a plot showing the jump when RTX was turned off. The RTX is usually within ?ñ1 or 2 cm.?ÿ

Here is the vertical...

I also turned on a GGA NMEA output at 1 hz, and and capturing the data stream. I will post later today or tomorrow morning a plot of the WAAS positions.?ÿ

Note that the receiver is tracking 4 constellations, 30+ satellites. HOWEVER, when using WAAS it only uses the GPS satellites for the position computation.?ÿ

I should add that the reference position is NAD83 (2011) epoch 2010.0, transformed from ITRF2014 using HTDP including 60 days of data. This is because I use it as an internet base for RTK over cell.?ÿ

Considering that the goal of WAAS is to support air navigation, and WAAS specs/goals are for ~8m accuracy at the 95% confidence level, and the last several realizations of ITRF (going back twenty years to ITRF2000) have transformation parameters of a few millimeters between them, it really doesn't matter what WAAS is broadcasting. (I guess there could be?ÿ

Even considering that the real-world accuracy of WAAS is generally better than 8m, any differences between current ITRF parameters and a WAAS-broadcast correction of another realization of WAAS is going to be buried deep in that 1-3 meters of accuracy that WAAS is good for.

Generally speaking, even RTK is going to have a hard time differentiating between two, and even three, adjacent realizations of ITRF.

The differences between the more recent various realizations of ITRF is generally at the mm level.?ÿ

For example, the difference between ITRF2014 and ITRF2020 at epoch 2015.0 is:

Much larger differences are due to the velocities (i.e. plate motion), which varies depending on what plate the station is on (and also where on the plate) and what epoch is used. Where I am located, in western PA, the velocities are relatively small, but there are stations with velocities greater than 5 cm/year.?ÿ?ÿ

5 hours of WAAS:

Horizontal:?ÿ

Vertical:?ÿ

And finally, 24hurs...the blue is ITRF14 current epoch...

Thanks to everyone for the replies and especially to John for the graphs. The SXblue II makes no transformations to WAAS solution, leaving it in the ITRF in use. The points are well taken that which ITRF makes no practical difference. I just wanted to set it to the one in use, if possible. John's graphs show the same kind of wandering delta in all 3 axes that I have seen with WAAS. This pretty well defines it's accuracy. With 4 constellations, and WAAS on GPS, I have achieved 7 inch accuracy on a USGS benchmark on a mountain top with 1 hour of data. This benchmark has an accuracy of amount +/- 2 cm but provides a clear sky for a best case test.