NAD83(2011)

NAD83(CONUS) Molodensky has transformation parameters of 0,0,0.

You do not need any other file as long as you put a NAD83(2011) coordinate in for your base.

What if I don't have a NAD83(2011) coordinate for my base?

what coordinate do you have for your base?

I take an autonomous reading when the job begins. If I have the NAD83(Conus)(Mol) datum in my data collector won't I have just a NAD83 coordinate for my base?

then you will have a WGS84 position ± a few meters. Since the transformation is 0,0,0 that is what you will have. Not worth the trouble to transform n autonomous position from WGS84 to NAD83, as the accuracy of your position is probably less than the transformation.

I get what you're saying.

Just for curiosity's sake, is there a good paper/article on the actual transformation from NAD83 to NAD83(2011), and maybe a piece of software that can be used to perform the transformation?

> Just for curiosity's sake, is there a good paper/article on the actual transformation from NAD83 to NAD83(2011), and maybe a piece of software that can be used to perform the transformation?

This page provides transformation parameters between NAD83 and IGS08 (the IGS version of ITRF2008), which itself is coincident with WGS84(G1674) at the centimeter level per this page.

NAD 83, NAD83(86), NAD83(93), NAD83(2011) are just NAD83 updated to more "accurate" coordinates, it's important to know the Epoch that you're in cause there ever so small changes to the coordinates of points on the earth, and they are changing also because of drift.

So it isn't so much a conversion between systems such as NAD83 and WGS84.

When you set your Trimble up with NAD83 you get NAD83(2011) from your control so you are NAD83(2011). The control controls that, you can't just start your receiver and be on it.

NAD83 realizations are tied as best possible to fixed positions on the North American tectonic plate, so there is very little drift between realizations.

WGS84, the native GPS datum, is tied to an average of stations around the world, so NAD83 drifts significantly over years with respect to WGS84.

> I'm using an R6-2 rover & TSC3 w/Trimble Access on the Western Data Systems VRS network, which broadcasts NAD83(2011) adjustments. I've downloaded, and can use, the Geoid12A file, but if I wanted to use a stand-alone base, where can I download the NAD83(2011) datum file? My TSC3 currently only has the NAD83(Conus)(Mol).
>
> Thanks in advance for your help.

Do not use anything other than the NAD 83(Conus) file. We had NAD83(2011) template setup first (came with the collector) and it applied a double correction. Whatever NAD83 coordinate you put in the base (i.e. 2011, CORS96, etc) will be the NAD83 coordinate system you are on.

I was told some time ago that WGS84 wasn't really available for use, that it is not convertible from NAD83, in the same way you cant really change between NAD83 and NAD27 by some conversion program.

That one (NAD83 to 27)I know very well (and no it doesn't work), but since I can't really check into WGS84 I just don't know if any conversion actually works.

> Whatever NAD83 coordinate you put in the base (i.e. 2011, CORS96, etc) will be the NAD83 coordinate system you are on.

Correct me if I'm wrong but I think what he is saying is that the coordinates in the base are from a "Here" shot and he wants the most accurate "Here" shot that he can get.

For my area that would be about -1.8' north adjustment and +3.0 east adjustment. That would get me to within 10 feet more or less, on a good day. 5 feet if I wait for waas correction before hitting the "here" button.

Not sure it would be worth the effort. That's what OPUS is for.

James

The programs available for converting 27 to 83 are limited. I have found areas where it is near useless. On the other hand I work in locations where NADCON gives great results. The same is true for Vertcon and the vertical datums. It's not that the tools don't work. They just don't work well everywhere....

There is no conversion from the original NAD83 to NAD83/2011. About the only thing you can do is occupy existing NAD83 original coordinates around your job site to generate NAD83/2011 coordinates and then create a local transformation. If that makes sense.

> > Just for curiosity's sake, is there a good paper/article on the actual transformation from NAD83 to NAD83(2011), and maybe a piece of software that can be used to perform the transformation?
>
> This page provides transformation parameters between NAD83 and IGS08 (the IGS version of ITRF2008), which itself is coincident with WGS84(G1674) at the centimeter level per this page.

Along these lines how do you best get from a WAAS here position to NAD83?

You know the shifts in your area but that varies in location. I work all over the US.

I always collect data for OPUS but many times I have to start work with a here position and correct it after the fact. The closer I can get the here position the better.

> I always collect data for OPUS but many times I have to start work with a here position and correct it after the fact. The closer I can get the here position the better.

The rule of thumb I recall is that a 10-meter error in base position introduces a 1 ppm error in the vectors. Even a cheap WAAS-corrected handheld should be able to do better than that, often by a factor of 5. Given the other error sources inherent in the RTK approach, I wouldn't think that 1 ppm would be much of a problem.

The programs "work" everywhere I've ever used them. They produce a number, input 83 and they kick out a 27 value. Have you ever checked that 27 value against the actual 27 value? I have, I've done extensive checking of the numbers and they have never matched. The closest has been. 5', but I've seen up to 6'. Other surveyors I've talked to have told me they've seen 15' and someone told me 30', but I never saw that,

Once I saw 6' on a first order 27 monument I quit looking at it. That was years ago. So when I actually need a 27 # I survey in the 27 system and don't use the stretch and fit program.

Vertical is different, they get you closer. My testing of those show from .1' to. 7'. A factor of ten "closer" than the horizontal. When I've tested geiod models against actual geoid slopes, the newer ones preform better with each update.

> Along these lines how do you best get from a WAAS here position to NAD83?

I get a better WGS84 position from the WAAS correction and I know the shift between the NAD83 (2011) and the IGS08 (WGS84) from previous OPUS results in the area. My correction may be off a tenth or two but the correction is applied to a point that is only accurate to 3-5 feet.

I would much rather log a file for OPUS ahead of time but can't always do that.

I can't answer your question in regards to anywhere in the US.
There should be conversions on the NGS website to do that but I don't use them.

James

NADCON is the official datum transformation tool for the U.S. to go between NAD 27 and NAD 83. It has a standard deviation of 0.15m (.5') in the lower 48. I have seen a few occasions where it was slightly higher but rarely in the range of more than about 0.5m (1.6 ft). NGS has created a transformation tool to go from each state's HARN to NAD 83 (2007) called GEOCON and from 2007 to NAD 83 (2011) called GEOCON11. They provide excellent results but they are a pain in the rear to use. -- GEOCON